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vms/gawk.hlp
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Arnold D. Robbins
VMS updates, including gawk.hlp.
25 май 2011, 23:13
25 май 2011, 23:13
5f7754a
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! Gawk.Hlp ! Pat Rankin, Jun'90 ! revised, Jun'91 ! revised, Jul'92 ! revised, Jan'95 ! revised, Apr'97 ! revised, Jan'03 ! revised, May'11 ! Online help for GAWK. ! 1 GAWK GAWK is GNU awk, the Free Software Foundation's implementation of the awk programming language. awk is an interpretive language which can handle many data-reformatting jobs with just a few lines of code. It has powerful string manipulation and pattern matching capabilities built in. This version is compatible with POSIX 1003.2 awk. The VMS version of GAWK supports both the original UN*X-style command interface and a DCL interface. The only setup requirement for GAWK is to define it as a 'foreign' command: a DCL symbol with a value which begins with '$'. $ GAWK :== $disk:[directory]GAWK 2 GNU_syntax GAWK's UN*X-style interface uses the 'dash' convention for specifying options and uses spaces to separate multiple arguments. There are two main alternatives, depending on how the awk program is to be passed to GAWK. Both alternatives share most options. Usage: $ gawk [-Wopts] [-F fs] [-v var=val] -f progfile [--] file ... or $ gawk [-Wopts] [-F fs] [-v var=val] [--] "program" file ... The options are case-sensitive. On VMS, the DCL command interpreter converts unquoted text into uppercase before passing it to the running program. However, GAWK is written in 'C' and the C Run-Time Library (VAXCRTL or DECC$SHR) converts unquoted text into *lowercase*. Therefore, the -Fval and -W options must be enclosed in quotes. 3 options -d[file] dump variable values into file (default is awkvars.out if not specified) upon program completion -e program_text additional program text, as a quoted string, for use in combination with -f -f file use the specified file as the awk program source; if more than one instance of -f is used, each file will be read in succession -Fstring define a value for the FS variable (field separator) -O optimize; of limited use -p[file] write program execution profiling into file (default is awkprof.out if not specified) -v var=val assign a value of 'val' to the variable 'var' -W'options' additional gawk-specific options; multiple values may be separated by commas, or by spaces if they're quoted, or mulitple occurrences of -W may be used. -Wcopyright display an abbreviated version of the GNU copyright information -Whelp list command line options (supersedes -Wusage) -Wlint warn about suspect or non-portable awk program code -Wlint=fatal treat lint warnings as errors -Wlint-old warn about constructs not available in original awk -Wposix traditional mode with additional restrictions -Wre-interval evaluate '{' and '}' as intervals in regular expressions -Wtraditional use awk compatibility mode to disable GAWK extensions and get the behavior of UN*X awk. -Wversion display program version number -- don't check further arguments for leading dash 3 program_text If the '-f file' option is not used on the command line, then the first "non-dash" argument is assumed to be a string of text containing the awk source program. Here is a complete sample program: $ gawk -- "BEGIN {print ""\nHello, World!\n""}" This program would print a blank line (based on first "\n"), followed by a line reading "Hello, World!", followed by another blank line (since awk's 'print' statement includes the trailing 'newline'). On VMS, to include a quote character inside of a quoted string, two successive quotes ("") must be used. 3 data_files After all dash-options are examined, and after the program text if there were no occurrences of the -f option, remaining (space separated) command line arguments are considered to be data files for the awk program to process. If any of these actually contains an equals sign (=), then it is interpreted as a variable assignment instead of a data file. The syntax is 'variable_name=value'. For example, the command $ gawk -f myprog.awk infile.one flag=2 start=0 infile.two would read file 'infile.one' for the program in 'myprog.awk', then it would set 'flag' to 2 and 'start' to 0, and finally it would read file 'infile.two' for the program. Note that in a case like this, the two assignments actually occur after the first file has been processed, not at program startup when the command line is first scanned. 3 IO_redirection The command parsing in the VMS implementation of GAWK does some emulation of a UN*X-style shell, where certain characters on the command line have special meaning. In particular, the symbols '<', '>', '|', '*', and '?' receive special handling before the main part of the program has a chance to see them. The symbols '<' and '>' perform some file manipulation from the command line: <ifile open file 'ifile' (readonly) as 'stdin' [SYS$INPUT] >nfile create 'nfile' as 'stdout' [SYS$OUTPUT], in stream-lf format >>ofile append to 'ofile' for 'stdout'; create it if necessary >&efile point 'stderr' [SYS$ERROR] at 'efile', but don't open it yet >$vfile create 'vfile' as 'stdout', using RMS attributes appropriate for a standard text file (variable length records with implied carriage control) >+bfile create 'bfile' as 'stdout' using binary mode 2>&1 route error messages into the regular output stream 1>&2 send output data to the error destination <<sentinel error; reading stdin until 'sentinel' not supported <-, >- error; closure of stdin or stdout from cmd line not supported >>$vfile incorrect; would be interpreted as file "$vfile" in stream-lf format rather than as file "vfile" in RMS 'text' format | error; command line pipes not supported 3 wildcard_expansion The command parsing in the VMS implementation of GAWK does some emulation of a UN*X-style shell, where certain characters on the command line have special meaning. In particular, the symbols '<', '>', '*', '%', and '?' receive special handling before the main part of the program has a chance to see them. The symbols '*', '%' and '?' are used as wildcards in filenames. '*' and '%' have their usual VMS meanings of multiple character and single character wildcards, respectively, and '?' is also treated as a single character wildcard. Wildcard expansion only works for filenames specified in native VMS filename syntax (eg, "[-.sibling]*"), not for ones specified pseudo- Unix syntax (eg, "../sibling/*"). When a command line argument that should be a filename contains any of the wildcard characters, a directory lookup is attempted for files which match the specified pattern. If one or more matching files are found, those filenames are put into the command line in place of the original pattern. If no matching files are found, the original pattern is left in place. 2 DCL_syntax GAWK's DCL-style interface is more or less a standard DCL command, with one required parameter. Multiple values--when present--are separated by commas. There are two main alternatives, depending on how the awk program is to be passed to GAWK. Both alternatives share most options. Usage: GAWK /COMMANDS="awk program text" data_file[,data_file,...] or GAWK /INPUT=awk_file data_file[,"Var=value",data_file,...] ( or GAWK /INPUT=(awk_file1,awk_file2,...) data_file[,...] ) 3 Parameter data_file[,datafile,...] (data_file data_file ...) data_file[,"Var=value",...,data_file,...] (data_file Var=value &c) Data file(s) for the awk program to process. If any of these actually contains an equals sign (=), then it is interpreted as a variable assignment instead of a data file. The syntax is "variable_name=value". Quotes are required for non-file parameters. For example, the command $ gawk/input=myprog.awk infile.one,"flag=2","start=0",infile.two would read file 'infile.one' for the program in 'myprog.awk', then it would set 'flag' to 2 and 'start' to 0, and finally it would read file 'infile.two' for the program. Note that in a case like this, the two assignments actually occur after the first file has been processed, not at program startup when the command line is first scanned. Wildcard file lookups are attempted on data file specifications. See subtopic 'GAWK GNU_syntax wildcard_expansion' for details. At least one data_file parameter value is required. An exception is made if /usage, /version, or /copyright is specified *and* if GAWK is defined as a 'foreign' command rather than a 'native' DCL command. 3 Qualifiers /COMMANDS /COMMANDS="awk program text" (-- "awk program text") For short programs, it is possible to include the complete program on the command line. The quotes are required. Here is a complete sample program: $ gawk/commands="BEGIN {print ""\nHello, World!\n""}" NL: This program would print a blank line (based on first "\n"), followed by a line reading "Hello, World!", followed by another blank line (since awk's 'print' statement includes the trailing 'newline'). To include a quote character inside of a quoted string, two successive quotes ("") must be used. Either /COMMANDS or /INPUT (but not both) must be supplied. /INPUT /INPUT=(awk_file1,awk_file2) (-f awk_file1 -f awk_file2) Used to specify one or more files containing the source code of the awk program. If more than one file is used, separate them with commas and enclose the list in parentheses. Multiple source files are processed in order as if they had been concatenated together. Either /INPUT or /COMMANDS (but not both) must be supplied unless one of /VERSION, /COPYRIGHT, and /USAGE is used. /EXTRA_COMMANDS /EXTRA_COMMANDS="awk program text" (-E "awk program text") Add more program text, for use in combination with /INPUT. Unlike Un*x or GNU syntax processing of VMS GAWK where multiple instances of -f file and -e text can be interspersed, DCL command processing of VMS GAWK allows only one /EXTRA_COMMANDS="text" qualifier and handles it before /INPUT=(file,...). /FIELD_SEPARATOR /FIELD_SEPARATOR="FS_value" (-F"FS_value") Assign a value to the built in variable FS (field separator). /VARIABLES /VARIABLES=("Var1=val1","Var2=val2",...) (-v Var1=val1 -v Var2=val2) Assign value(s) to the specified variable(s). /OPTIMIZE /[NO]OPTIMIZE (-"O" option) Perform some relatively minor optimizations on the source code as it is read in; primarily constant folding. Default is /NOOPTIMIZE but presently optimization is always enabled and explicitly negating it has no effect. This may change when/if more elaborate optimizations are implemented. /PROFILE /PROFILE[=file] (-p[file]) Write profiling feedback into the specified file. If no file name is specified, awkprof.out in the current directory is used. /DUMP_VARIABLES /DUMP_VARIABLES[=file] (-d[file]) Print a sorted list of global variables, their types, and final values to the specified file. If no file name is specified, awkvars.out in the current directory is used. !-/REG_EXPR !- /REG_EXPR={AWK | EGREP | POSIX} (-a vs -e options [obsolete]) !- !- This qualifier is obsolete and has no effect. /POSIX /[NO]POSIX (-"Wposix" option) Use POSIX compatibility mode (/posix) and suppress GAWK extensions. The default is /NOPOSIX. Slightly more restrictive than /strict. /TRADITIONAL /[NO]TRADITIONAL (-"Wtraditional" option) Use strict awk compatibility mode (/traditional) and suppress GAWK extensions. Supersedes /STRICT. The default is /NOTRADITIONAL. /STRICT /[NO]STRICT (-"Wtraditional" option) Use strict awk compatibility mode (/strict) and suppress GAWK extensions. Superseded by /TRADITIONAL. The default is /NOSTRICT. /RE_INTERVAL /RE_INTERVAL (-"Wre-interval" option) Allow interval expressions in regexps (regular expressions). GAWK always accepts intervals in normal mode; /RE_INTERVAL can be used to enable them in strict (/TRADITIONAL) compatability mode. /SANDBOX /SANDBOX (-"Wsandbox" option) Disables the system() function, input redirections with getline, output redirections with print and printf, and dynamic extensions. /NON_DECIMAL_DATA /NON_DECIMAL_DATA (-"Wnon-decimal-data" option) Enable automatic interpretation of octal and hexadecimal values in input data. Use with care. /LINT /[NO]LINT[=(WARN,OLD,FATAL)] (-"Wlint" and -"Wlint-old" options) Check the awk program cafefully for potential problems that might be encountered if it were to be used with other awk implementations, and print warnings for anything found. The default in /NOLINT. /LINT without a value is equivalent to /LINE=WARN. /LINT=OLD warns about constructs which wouldn't work with /TRADITIONAL. /LINT=FATAL turns lint warnings into errors which cause GAWK to terminate. !- /LINT=INVALID is accepted but isn't documented here. !three undocumented qualifiers; judged not useful for VMS !- /CHARACTERS_AS_BYTES !- /CHARACTERS_AS_BYTES (-"Wcharacters-as-bytes" option) !- /USE_LC_NUMERIC !- /USE_LC_NUMERIC (-"Wuse-lc-numeric" option) !- /GEN_POT !- /GEN_POT (-"Wgen-pot" option) /VERSION /VERSION (-"Wversion" option) Print GAWK's version number and then terminate. Includes copyright notice. /COPYRIGHT /COPYRIGHT (-"Wcopyright" option) Print a brief version of GAWK's copyright notice and then terminate. /USAGE /USAGE (comparable to -"Whelp" option) Print a compact summary of the command line options. After the 'usage' message is printed, GAWK terminates regardless of any other command line options. /OUTPUT /OUTPUT=out_file (>$out_file) Write program output into 'out_file'. The default is SYS$OUTPUT. 2 awk_language An awk program consists of one or more pattern-action pairs, sometimes referred to as "rules". For each record of an input (data) file, the rules are checked sequentially. Any pattern which matches the input record triggers that rule's action. Actions are instructions which resemble statements in the 'C' programming language. Patterns come in several varieties, including field comparisons, regular expression matching, and special cases defined by reserved keywords. All awk keywords and variables are case-sensitive. Text matching is also sensitive to character case unless the builtin variable IGNORECASE is set to a non-zero value. 3 rules The syntax for a pattern-action 'rule' is simply PATTERN { ACTION } where the braces ({}) are required punctuation for the action. Semicolons (;) or 'newlines' (ie, having the text on a separate line) delimit multiple rules and also multiple actions within a given rule. Either the pattern or the action may be omitted; an empty pattern matches every record of the input file; a missing action (not an empty action inside of braces), is an implicit request to print the current record; an empty action (ie, {}) is legal but not very useful. 3 patterns There are several types of patterns available for awk rules. expression an 'expression' is something to be evaluated (perhaps a comparison or function call) which will be considered true if non-zero (for numeric results) or if non-null (for strings) /regular_expression/ slashes (/) delimit a regular expression which is used as a pattern pattern1, pattern2 a pair of patterns separated by a comma (,), which causes a range of records to trigger the associated action; the records which match the patterns are included in the range <null> an omitted pattern (in this text, the string '<null>' is displayed, but in an awk program, it would really be blank) matches every record BEGIN keyword for specifying a rule to be executed prior to reading the 1st record of the 1st input file END keyword for specifying a rule to be executed after handling the last input record of last file BEGINFILE gawk-specific keyword for specifying a rule to be executed when a file from the command line has just been opened, before attempting to read its first record ENDFILE gawk-specific keyword for specifying a rule to be executed after the last record of a file from the command has been processed by any other patterns and actions 4 BEGINFILE Normally a file open attempt which fails will generate an error and cause GAWK to terminate. However, if your program has a BEGINFILE rule, failed open attempts will set ERRNO to a non-null value and execute the BEGINFILE rule's actions. You can check for that condition and use the 'nextfile' statement to skip files which couldn't be opened. Note that when executing the BEGINFILE rule for a failed open attempt, allowing the actions to finish without using 'nextfile' will result in an error just like for a program which has no BEGINFILE rule. 4 examples Some example patterns (mostly with the corresponding actions omitted) NF > 0 # comparison expression: matches non-null records $0 # implied comparison: also matches non-null records $2 > 1000 && sum <= 999999 # slightly more elaborate expression /x/ # regular expression matching any record with an 'x' in it /^ / # reg-expr matching records beginning with a space $1 == "start", $NF == "stop" # range pattern for input in which some data lines begin with 'start' and/or end with 'stop' in order to collect groups of records { sum += $1 } # null pattern: it's action (add field #1 to variable 'sum') would be executed for every record BEGIN { sum = 0 } # keyword 'BEGIN': perform this action before reading the input file (note: initialization to 0 is unnecessary in awk) END { print "total =", sum } # keyword 'END': perform this action after the last input record has been processed # two different ways to handle the start of an input file: FNR == 1 { print FILENAME } # print name after reading first record BEGINFILE { print FILENAME } # print name before reading first record 3 actions An 'action' is something to do when a given record has matched the corresponding pattern in a rule. In general, actions resemble 'C' statements and expressions. The action in a rule must be enclosed in braces ({}). Each action can contain more than one statement or expression to be executed, provided that they're separated by semicolons (;) and/or on separate lines. An omitted action is equivalent to { print $0 } which prints the current record. 3 operators Relational operators == compare for equality != compare for inequality <, <=, >, >= numerical or lexical comparison (less than, less or equal, greater than, greater or equal, respectively) ~ match against a regular expression !~ match against a regular expression, but accept failed matches instead of successful ones Arithmetic operators + addition - subtraction * multiplication / division % remainder ^, ** exponentiation ('**' is a synonym for '^', unless POSIX compatibility is specified, in which case it's invalid) Boolean operators (aka Logical operators) a value is considered false if it's 0 or a null string, it is true otherwise; the result of a boolean operation (and also of a comparison operation) will be 0 when false or 1 when true || or [expression (a || b) is true if either a is true or b is true or both a and b are true; it is false otherwise; b is not evaluated unless a is false (ie, short-circuit)] && and [expression (a && b) is true if both a and b are true; it is false otherwise; b is only evaluated if a is true] ! not [expression (!a) is true if a is false, false otherwise] in array membership; the keyword 'in' tests whether the value on the left represents a current subscript in the array named on the right Conditional operator ? : the conditional operator takes three operands; the first is an expression to evaluate, the second is the expression to use if the first was true, the third is the expression to use if it was false [simple example (a < b ? b : a) gives the maximum of a and b] Assignment operators = store the value on the right into the variable or array slot on the left [expression (a = b) stores the value of b in a] +=, -=, *=, /=, %=, ^=, **= perform the indicated arithmetic operation using the current value of the variable or array element of the left side and the expression on the right side, then store the result in the left side ++ increment by 1 [expression (++a) gets the current value of a and adds 1 to it, stores that back in a, and returns the new value; expression (a++) gets the current value of a, adds 1 to it, stores that back in a, but returns the original value of a] -- decrement by 1 (analogous to increment) String operators there is no explicit operator for string concatenation; two values and/or variables side-by-side are implicitly concatenated into a string (numeric values are first converted into their string equivalents) Conversion between numeric and string values there is no explicit operator for conversion; adding 0 to a string with force it to be converted to a number (the numeric value will be 0 if the string does not represent an integer or floating point number); the reverse, converting a number into a string, is done by concatenating a null string ("") to it [the expression (5.75 "") evaluates to "5.75"] Field 'operator' $ prefixing a number or variable with a dollar sign ($) causes the appropriate record field to be returned [($2) gives the second field of the record, ($NF) gives the last field (since the builtin variable NF is set to the number of fields in the current record)] Array subscript operator , multi-dimensional arrays are simulated by using comma (,) separated array indices; the actual index is generated by replacing commas with the value of builtin SUBSEP, then concatenating the expression into a string index [comma is also used to separate arguments in function calls and user-defined function definitions] [comma is *also* used to indicate a range pattern in an awk rule] Escape 'operator' \ In quoted character strings, the backslash (\) character causes the following character to be interpreted in a special manner [string "one\ntwo" has an embedded newline character (linefeed on VMS, but treated as if it were both carriage-return and linefeed); string "\033[" has an ASCII 'escape' character (which has octal value 033) followed by a 'right-bracket' character] Backslash is also used in regular expressions Redirection operators < Read-from -- valid with 'getline' > Write-to (create new file) -- valid with 'print' and 'printf' >> Append-to (create file if it doesn't already exist) | Pipe-from/to -- valid with 'getline', 'print', and 'printf' 4 precedence Operator precedence, listed from highest to lowest. Assignment, conditional, and exponentiation operators group from right to left; all others group from left to right. Parentheses may be used to override the normal order. field ($) increment (++), decrement (--) exponentiation (^, **) unary plus (+), unary minus (-), boolean not (!) multiplication (*), division (/), remainder (%) addition (+), subtraction (-) concatenation (no special symbol; implied by context) relational (==, !=, <, >=, etc), and redirection (<, >, >>, |) Relational and redirection operators have the same precedence and use similar symbols; context distinguishes between them matching (~, !~) array membership ('in') boolean and (&&) boolean or (||) conditional (? :) assignment (=, +=, etc) 4 escaped_characters Inside of a quoted string or constant regular expression, the backslash (\) character gives special meaning to the character(s) after it. Special character letters are case sensitive. \\ results in one backslash in the string \a is an 'alert' (<ctrl/G>. the ASCII <bell> character) \b is a backspace (BS, <ctrl/H>) \f is a form feed (FF, <ctrl/L>) \n 'newline' (<ctrl/J> [line feed treated as CR+LF] \r carriage return (CR, <ctrl/M> [re-positions at the beginning of the current line] \t tab (HT, <ctrl/I>) \v vertical tab (VT, <ctrl/K>) \### is an arbitrary character, where '###' represents 1 to 3 octal (ie, 0 thru 7) digits \x## is an alternate arbitrary character, where '##' represents 1 or more hexadecimal (ie, 0 thru 9 and/or A through E and/or a through e) digits; if more than two digits follow, the result is undefined; not recognized if POSIX compatibility mode is specified. When a regular expression is represented in string form ("regex" as opposed to /regex/), backslashes need to be paired. The first one quotes the second during string processing, and the second one remains to be used to quote whatever follows in regular expression processing. For example, to match variable `xxx' against a period character, use (xxx ~ "\\.") or (xxx ~ /\./); if you tried to use (xxx ~ "\."), after string processing it would operate as (xxx ~ /./) and end up matching any single character rather than just a period. 3 statements A statement refers to a unit of instruction found in the action part of an awk rule, and also found in the definition of a function. The distinction between action, statement, and expression usually won't matter to an awk programmer. Compound statements consist of multiple statements separated by semicolons or newlines and enclosed within braces ({}). They are sometimes referred to as 'blocks'. 4 expressions An expression such as 'a = 10' or 'n += i++' is a valid statement. Function invocations such as 'reformat_field($3)' are also valid statements. 4 if-then-else A conditional statement in awk uses the same syntax as for the 'C' programming language: the 'if' keyword, followed by an expression in parentheses, followed by a statement--or block of statements enclosed within braces ({})--which will be executed if the expression is true but skipped if it's false. This can optionally be followed by the 'else' keyword and another statement--or block of statements-- which will be executed if (and only if) the expression was false. 5 examples Simple example showing a statement used to control how many numbers are printed on a given line. if ( ++i <= 10 ) #check whether this would be the 11th printf(" %5d", k) #print on current line if not else { printf("\n %5d", k) #print on next line if so i = 1 #and reset the counter } Another example ('next' is described under 'action-controls') if ($1 > $2) { print "rejected"; next } else diff = $2 - $1 4 switch-case A gawk extension provides an alternative for conditional execution to the if-then-else construct. The switch statement takes a value to use to decide which of one or more case clauses to execute, similar to the same construct in C and C++. The main difference is that in those languages, the case values must be constant integers, whereas in awk they can by numbers, strings, or regular expressions. Like in C/C++, an optional 'default' clause can be specified to serve as a catch-all for values which don't match any of the cases. The first case which matches the switch value is the one which will be executed. If it doesn't use one of 'break', 'continue', 'next', 'nextfile', 'return', or 'exit', then execution will continue into the body of the next case. (Note that 'continue' doesn't operate as an explicit request to do such; rather, it causes execution of an enclosing for, while, or do-while statement to jump to the end of its loop.) 5 example In this example, the value of variable 'x' is examined. It contains a mistake that someone coming from a background of programming in Pascal might accidentally make. switch (x) { case 1: print "x is 1"; break; case 2: print "x is 2" case "two": print "x is \"two\""; break; default: print "x is neither 1 nor 2"; break } Note that if the value is '2', after printing "x is 2" it will continue into the next case and also print "x is \"two\"", which was probably not intended. The 'break' statement is needed to jump out of the switch statement instead of falling through into the subsequent clause. For the very last one, 'default' in this example, 'break' is optional; reaching the closing bracket of a switch statement also breaks out of the statement. 4 loops Three types of loop statements are available in awk. Each uses the same syntax as 'C'. The simplest of the three is the 'while' statement. It consists of the 'while' keyword, followed by an expression enclosed within parentheses, followed by a statement--or block of statements in braces ({})--which will be executed if the expression evaluates to true. The expression is evaluated before attempting to execute the statement; if it's true, the statement is executed (the entire block of statements if there is a block) and then the expression is re-evaluated. The second type of loop is the do-while loop. It consists of the 'do' keyword, followed by a statement (usually a block of statements enclosed within braces), followed by the 'while' keyword, followed by a test expression enclosed within parentheses. The statement--or block--is always executed at least once. Then the test expression is evaluated, and the statement(s) re-executed if the result was true (followed by re-evaluation of the test, and so on). The most complex of the three loops is the 'for' statement, and it has a second variant that is not found in 'C'. The ordinary for-loop consists of the 'for' keyword, followed by three semicolon-separated expressions enclosed within parentheses, followed by a statement or brace-enclosed block of statements. The first of the three expressions is an initialization clause; it is done before starting the loop. The second expression is used as a test, just like the expression in a while-loop. It is checked before attempting to execute the statement block, and then re-checked after each execution (if any) of the block. The third expression is an 'increment' clause; it is evaluated after an execution of the statement block and before re-evaluation of the test (2nd) expression. Normally, the increment clause will change a variable used in the test clause, in such a fashion that the test clause will eventually evaluate to false and cause the loop to finish. Note to 'C' programmers: the comma (,) operator commonly used in 'C' for-loop expressions is not valid in awk. The awk-specific variant of the for-loop is used for processing arrays. Its syntax is 'for' keyword, followed by variable_name 'in' array_name (where 'var in array' is enclosed in parentheses), followed by a statement (or block). Each valid subscript value for the array in question is successively placed--in no particular order--into the specified 'index' variable. Order can optionally be controlled by assigning a sort mode to PROCINFO["sorted_in"]. 5 while_example # strip fields from the input record until there's nothing left while (NF > 0) { $1 = "" #this will affect the value of $0 $0 = $0 #this causes $0 and NF to be re-evaluated print } 5 do_while_example # This is a variation of the while_example; it gives a slightly # different display due to the order of operation. # echo input record until all fields have been stripped do { print #output $0 $1 = "" #this will affect the value of $0 $0 = $0 #this causes $0 and NF to be re-evaluated } while (NF > 0) 5 for_example # echo command line arguments (won't include option switches) for ( i = 0; i < ARGC; i++ ) print ARGV[i] # display contents of builtin environment array for (itm in ENVIRON) print itm, ENVIRON[itm] 5 for_index_in_array_sorting Normally indices in an array are processed in an arbitrary order when using the 'for (index in array)' statement, but a gawk-extension allows you to control that order. Assign a value to the "sorted_in" element of the PROCINFO[] array to accomplish this. The value may be a comparison function which accepts four arguments (index and value of one element, then index and value of another), or a special value which specifies one of several built-in comparison functions. These functions are used to compare pairs of array elements and their result controls which of each pair comes before the other. 6 comparison_function A function assigned to PROCINFO["sorted_in"] should be prepared to accept four arguments and to return a numeric value, negative if the element specified by the first two arguments (its index and its value, respectively) is less than the element specified the second pair of arguments, zero if they compare equal, and positive of the first element is greater than the second. Here's an example: function my_compare(idx1, val1, idx2, val2) { if (val1 < val2) return -1 if (val2 > val2) return 1 # the two values are equal return (idx1 < idx2) ? -1 : (idx1 > idx2) } This compares the two values and returns either negative or positive if they're different. If they're the same, it compares the two indices as a tie-breaker instead of simply returning zero. You can force values to be numeric or to be string, as needed, and use more elaborate ordering criteria. Just be sure that the results are consistent; returning a positive value when idx1,val1 is compared to idx2,val2 and then also returning a positive value if idx2,val2 gets compared to idx1,idx2 will likely confuse the sort routine and produce strange results. If you plan to sort arrays which contain sub-arrays (array elements which contain their own arrays) and you're sorting by value rather than by index, your compare routine should use the isarray() function to check for them (test second and fourth arguments to see whether they're arrays) and handle them appropriately. The basic comparison operators like '<' will produce an error if used on arrays. 6 built-in_comparisons Here is a list of built-in compare routines that can be assigned to PROCINFO["sorted_in"]. They are strings and start with '@' so that these names can't be confused with actual functions. "@ind_str_asc" order by indices compared as strings (all array indices are strings internally, even when they were assigned as numbers) "@ind_num_asc" order by indices compared as numbers (non-numeric ones end up with value 0) "@val_type_asc" order by values using assigned type (if a mixture of strings and numbers is present, numbers come first, then strings) "@val_str_asc" order by values compared as strings "@val_num_asc" order by values compared as numbers "@ind_str_desc" \ "@ind_num_desc" \ "@val_type_desc" descending versions of the above "@val_str_desc" / "@val_num_desc" / "@unsorted" explicitly specify arbitrary order (same as deleting the "sorted_in" element from the PROCINFO[] array, or never having assigned it a value in the first place) All the ascending sorts put sub-arrays--if any--last, and descending ones place them first. When multiple sub-arrays are present, they tie with each other without regard to their contents; such ties are then disambiguated by comparing their indices. 6 processing_order Sorting of the array takes place as the 'for (index in array)' statement is about to start executing. Changing the value of PROCINFO["sorted_in"] during the course of the loop will not affect traversal order, and could be used to control ordering of sub-arrays using different criteria. After the loop finishes, any ordering imposed on the indices is forgotten. A subsequent 'for (index in array)' traversal of the same array will yield whatever order is specified by PROCINFO["sorted_in"] at that time, including reverting to arbitrary if it no longer has a value. 4 loop-controls There are two special statements--both from 'C'--for changing the behavior of loop execution. The 'continue' statement is useful in a compound (block) statement; when executed, it effectively skips the rest of the block so that the increment-expression (only for for-loops) and loop-termination expression can be re-evaluated. The 'break' statement, when executed, effectively skips the rest of the block and also treats the test expression as if it were false (instead of actually re-evaluating it). In this case, the increment-expression of a for-loop is also skipped. Inside nested loops, both 'break' and 'continue' only apply to the innermost loop. When in compatibility mode, 'break' or 'continue' may be used outside of a loop; either will be treated like 'next' (see action-controls). 4 action-controls There are two special statements for controlling statement execution. The 'next' statement, when executed, causes the rest of the current action and all further pattern-action rules to be skipped, so that the next input record will be immediately processed. This is useful if any early action knows that the current record will fail all the remaining patterns; skipping those rules will reduce processing time. A GAWK extension, 'nextfile', is also available. It causes the remainder of the current file to be skipped, the ENDFILE action, if applicable, to be performed, and then the next input file will be processed. If there is no next input file, the END action will be performed. 'nextfile' is not available in traditional awk. The 'exit' statement causes GAWK execution to terminate. All open files are closed, and no further processing is done. The END rule, if any, is executed. 'exit' takes an optional numeric value as a argument which is used as an exit status value, so that some sort of indication of why execution has stopped can be passed on to the user's environment. 4 other_statements The delete statement is used to remove an element from an array. The syntax is 'delete' keyword followed by array name, followed by index value enclosed in square brackets ([]). As a gawk extension, 'delete' may also used on an array name without any index specified, to delete all its elements in a single operation. (The array itself will continue to exist as an array, even though it no longer contains any elements.) The return statement is used in user-defined functions. The syntax is the keyword 'return' optionally followed by a string or numeric expression. See also subtopic 'functions IO_functions' for a description of 'print', 'printf', and 'getline'. 3 fields When an input record is read, it is automatically split into fields based on the current values of FS (builtin variable defining field separator expression) and RS (builtin variable defining record separator character). The default value of FS is an expression which matches one or more spaces and tabs; the default for RS is newline. If the FIELDWIDTHS variable is set to a space separated list of numbers (as in ``FIELDWIDTHS = "2 3 2"'') then the input is treated as if it had fixed-width fields of the indicated sizes and the FS value will be ignored. The field prefix operator ($), is used to reference a particular field. For example, $3 designates the third field of the current record. The entire record can be referenced via $0 (and it holds the actual input record, not the values of $1, $2, ... concatenated together, so multiple spaces--when present--remain intact, unless a new value gets assigned). The builtin variable NF holds the number of fields in the current record. $NF is therefore the value of the last field. Attempts to access fields beyond NF result in null values (if a record contained 3 fields, the value of $5 would be ""). Assigning a new value to $0 causes all the other field values (and NF) to be re-evaluated. Changing a specific field will cause $0 to receive a new value once it's re-evaluated, but until then the other existing fields remain unchanged. 4 field_separation Three built in variables control separating input lines into fields, and the most recently assigned of those three is the one which has effect. PROCINFO["FS"] can be used to determine which one that is. FS is a character, string, or regular expression specifying what separates fields. It is available in all implementations of awk so is the most widely used. The default value is an explicit space and behaves as if the value was /[ \t\n]+/ to treat any number of spaces and tabs (and newlines, if RS isn't using them as record separators) as the separator. (Explicitly using that regular expression actually produces different results if the input happens to have leading and/or trailing whitespace. The default skips such space; the regexp increases NF by 1 and produces an empty $1 if there is leading whitespace and it increases NF by 1 and produces an empty $NF if there is trailing whitespace. To actually force the separator to be a single space, use the regular expression / /.) FIELDWIDTHS is a string containing a space-separated list of numbers which indicate how wide each field is. It is a gawk-extension and used to be considered experimental, but it has been in place for many years without significant changes. There is no default value, nor is there any way to specify a repeat count the way a Fortran FORMAT statment could. FPAT is a regular expression which specifies field values rather than the separation between fields. It is also a gawk-extension and is new with version 4.0.0. A gawk-extension makes setting FS to "" force each input character to be a separate field, similar to FIELDWIDTHS="1 1 1 1 1 1"(...) if you were able to supply an unlimited number of 1's. 3 variables Variables in awk can hold both numeric and string values and do not have to be pre-declared. In fact, there is no way to explicitly declare them at all. Variable names consist of a leading letter (either upper or lower case, which are distinct from each other) or underscore (_) character followed by any number of letters, digits, or underscores. When a variable that didn't previously exist is referenced, it is created and given a null value. A null value is treated as 0 when used as a number, and is a string of zero characters in length if used as a string. 4 builtin_variables GAWK maintains several 'built-in' variables. All have default values; some are updated automatically. All the builtins have uppercase-only names. These builtin variables control how awk behaves FS input field separator; default is a single space, which is treated as if it were a regular expression for matching one or more spaces and/or tabs and/or newlines; a value of " " also has a second special-case side-effect of causing leading and/or trailing blanks to be ignored instead of producing a null first and/or last field; initial value can be specified on the command line with the -F option (or /field_separator); the value can be a regular expression; as a gawk extension, if the value is an empty string (""), every character becomes a separate field RS input record separator; default value is a newline ("\n"); the value can be multiple characters or a regular expression OFS output field separator; value to place between variables in a 'print' statement; default is one space; can be arbitrary string ORS output record separator; value to implicitly terminate 'print' statement with; default is newline ("\n"); can be arbitrary string OFMT default output format used for printing numbers; default value is "%.6g" CONVFMT conversion format used for number-to-string conversions; default value is also "%.6g", like OFMT; not used when the number has a value which may be represented internally as an exact integer (typically within -2147483648 to 2147483647) SUBSEP subscript separator for array indices; used when an array subscript is specified as a comma separated list of values: the comma is replaced by SUBSEP and the resulting index is a concatenation of the values and SUBSEP(s); default value is "\034"; value may be arbitrary string IGNORECASE string and regular expression matching flag; if true (non-zero) matching ignores differences between upper and lower case letters; affects the '~' and '!~' operators, the 'index', 'match', 'split', 'sub', and 'gsub' functions, and field splitting based on FS; default value is false (0); has no effect if GAWK is in strict compatibility mode FIELDWIDTHS space or tab separated list of width sizes; takes precedence over FS when set, but is cleared if FS has a value assigned to it; [note: the current implementation of fixed-field input is considered experimental and is expected to evolve over time] FPAT an alternate way to specify fields, with a regexp pattern which defines field values rather than field separator [assigning a value to any of FS, FIELDWIDTHS, or FPAT causes the other two to be deactivated; the value of PROCINFO["FS"] can be used to determine which one is currently in use] BINMODE can be used force input and/or output files to be processed using binary I/O; a value of 1 or "r" forces binary mode when reading input, a value of 2 or "w" forces binary mode when writing output, and a value of 3 or "rw" causes GAWK to use binary mode for both input and output; BINMODE has no effect on reading from stdin or writing to stdout; they'll have already been opened in text mode before you assign a value LINT setting or unsetting this can dynamically toggle the --lint command line option on or off These builtin variables provide useful information NF number of fields in the current record NR record number (accumulated over all files when more than one input file is processed by the same program) FNR current record number of the current input file; reset to 0 each time an input file is completed RT record terminator, the input text which matched RS; not available when the `-Wtraditional' option is used RSTART starting position of substring matched by last invocation of the 'match' function; set to 0 if a match fails and at the start of each input record RLENGTH length of substring matched by the last invocation of the 'match' function; set to -1 if a match fails FILENAME name of the input file currently being processed; the special name "-" is used to represent the standard input ENVIRON array of miscellaneous user environment values; the VMS implementation of GAWK provides values for ["USER"] (the username), ["PATH"] (current default directory), ["HOME"] (the user's login directory), and "[TERM]" (terminal type if available) [all info provided by C RTL's environ] PROCINFO miscellaneous process information and assorted GAWK extensions which don't fit in elsewhere ERRNO information about the cause of failure for 'getline' or 'close' or for file open during a BEGINFILE rule; it is only set if an error has occurred, it isn't reset when any subsequent operation succeeds; the only exception is that it is reset prior to attempting to open a file so that BEGINFILE rule actions can distinguish between success and failure ARGC number of elements in the ARGV array, counting [0] which is the program name (ie, "gawk") ARGV array of command-line arguments (in [0] to [ARGC-1]); the program name (ie, "gawk") in held in ARGV[0]; command line parameters (data files and "var=value" expressions, but not program options or the awk program text string if present) are stored in ARGV[1] through ARGV[ARGC-1]; the awk program can change values of ARGC and ARGV[] during execution in order to alter which files are processed or which between- file assignments are made ARGIND current index into ARGV[] 4 arrays awk supports associative arrays to collect data into tables. Array elements can be either numeric or string, as can the indices used to access them. Each array must have a unique name, but a given array can hold both string and numeric elements at the same time. Arrays are one-dimensional only, but multi-dimensional arrays can be simulated using comma (,) separated indices, whereby a single index value gets created by replacing commas with SUBSEP and concatenating the resulting expression into a single string. Referencing an array element is done with the expression Array[Index] where 'Array' represents the array's name and 'Index' represents a value or expression used for a subscript. If the requested array element did not exist, it will be created and assigned an initial null value. To check whether an element exists without creating it, use the 'in' boolean operator. Index in Array would check 'Array' for element 'Index' and return 1 if it existed or 0 otherwise. To remove an element from an array, use the 'delete' statement delete Array[Index] To remove all array elements at once, use delete Array Note: the latter is a gawk extension; also, there is no way to delete an ordinary variable or an entire array; 'delete' only works on array elements. To process all elements of an array (in succession) when their subscripts might be unknown, use the 'in' variant of the for-loop for (Index in Array) { ... } (See the "awk_language statements loops" entry for a way to control the order of traversal with this construct.) Starting with version 4.0.0 array values can contain arrays, sometimes referred to as sub-arrays. They're created by assigning a value using multiple instances of subscripting: 'a[1][2] = 3' would create array a if it didn't already exist, create array element a[1] if it didn't already exist, create sub-array element a[1][2] if it didn't exist, then assign that the value 3. You can't directly assign an existing array to be a subarray: 'a[1] = 2; a[3] = 4; b["a"] = a' would get rejected. But you can produce the same effect by traversing the array and assigning it element by element: 'a[1] = 2; a[3] = 4; for (i in a) b["a"][i] = a[i]'. 3 functions awk supports both built-in and user-defined functions. A function may be considered a 'black-box' which accepts zero or more input parameters, performs some calculations or other manipulations based on them, and returns a single result. The syntax for calling a function consists of the function name immediately followed by an open parenthesis (left parenthesis '('), followed by an argument list, followed by a closing parenthesis (right parenthesis ')'). The argument list is a sequence of values (numbers, strings, variables, array references, or expressions involving the above and/or nested function calls), separated by commas and optional white space. The parentheses are required punctuation, except for the 'print' and 'printf' builtin IO functions, where they're optional, and for the builtin IO function 'getline', where they're not allowed. Some functions support optional [trailing] arguments which can be simply omitted (along with the corresponding comma if applicable). 4 numeric_functions Builtin numeric functions int(n) returns the value of 'n' with any fraction truncated [truncation of negative values is towards 0] sqrt(n) the square root of n exp(n) the exponential of n ('e' raised to the 'n'th power) log(n) natural logarithm of n sin(n) sine of n (in radians) cos(n) cosine of n (radians) atan2(m,n) arctangent of m/n (radians) rand() random number in the range 0 to 1 (exclusive) srand(s) sets the random number 'seed' to s, so that a sequence of 'random' numbers can be repeated; returns the previous seed value; srand() [argument omitted] sets the seed to an 'unpredictable' value (based on date and time, for instance, so should be unrepeatable) 4 string_functions Builtin string functions index(s,t) search string s for substring t; result is 1-based offset of t within s, or 0 if not found length(s) returns the length of string s; either 'length()' with its argument omitted or 'length' without any parenthesized argument list will return length of $0 match(s,r) search string s for regular expression r; the offset of the longest, left-most substring which matches is returned, or 0 if no match was found; the builtin variables RSTART and RLENGTH are also set [RSTART to the return value and RLENGTH to the size of the matching substring, or to -1 if no match was found] split(s,a,f,x) break string s into components based on field separator f and store them in array a (into elements [1], [2], and so on); the third argument is optional, if omitted, the value of FS is used; the fourth one is optional too, and is a gawk extension; when specified it should be an array which will receive the separators between the corresponding fields; the return value is the number of components found patsplit(s,a,p,x) similar to split, but p is a regexp pattern specifying field contents rather than a separator; if not specified, the value of FPAT is used; this function is a gawk extension sprintf(f,e,...) format expression(s) e using format string f and return the result as a string; formatting is similar to the printf function sub(r,t,s) search string target s for regular expression r, and if a match is found, replace the matching text with substring t, then store the result back in s; if s is omitted, use $0 for the string; the result is either 1 if a match+substitution was made, or 0 otherwise; if substring t contains the character '&', the text which matched the regular expression is used instead of '&' [to suppress this feature of '&', 'quote' it with a backslash (\); since this will be inside a quoted string which will receive 'backslash' processing before being passed to sub(), *two* consecutive backslashes will be needed "\\&"] gsub(r,t,s) similar to sub(), but gsub() replaces all nonoverlapping substrings instead of just the first, and the return value is the number of substitutions made gensub(r,t,n,s) search string s ($0 if omitted) for regexp r and replace the n'th occurrence with substring t; the result is the new string and s (or $0) remains unchanged; if n begins with letter "g" or "G" then all matches are replaced instead of just the n'th; if r has parenthesized subexpressions in it, t may contain the special sequences \\0, \\1, through \\9 which expand into the value of the corresponding subexpression; this function is a gawk extension substr(s,p,l) extract a substring l characters long starting at offset p in string s; l is optional, if omitted then the remainder of the string (p thru end) is returned tolower(s) return a copy of string s in which every uppercase letter has been converted into lowercase toupper(s) analogous to tolower(); convert lowercase to uppercase strtonum(s) convert string s into the corresponding number; if s begins with "0x", the rest of the string will be considered to be hexacimal digits, otherwise if it begins with "0" (not "o"), the rest will be treated as octal digits; this function is a gawk extension 4 array_functions isarray(a) returns 1 of a is an array, 0 otherwise; most useful when traversing an array which might contain array values (sub-arrays) split(s,a[,f[,x]]) break string s into components based on field separator f and store them in array a (into elements [1], [2], and so on); the third argument is optional, if omitted, the value of FS is used; the fourth one is optional too, and is a gawk extension; when specified it should be an array which will receive the separators between the corresponding fields; the return value is the number of components found patsplit(s,a[,p[,x]]) similar to split, but p is a regexp pattern specifying field contents rather than a separator; if not specified, the value of FPAT is used; this function is a gawk extension asort(s[,d[,m]]) sort the contents of array s, replacing the index values with an integer sequence of 1 to N; if d is specified, leave the indices of s intact and put the values and sequence index into d; if m is specified, it should be a string containing "ascending" or "descending" to control order, or "string" or "number" to control how comparisons are performed, or a combination of the two; m can also be a comparison function similar to ones used by PROCINFO["sorted_in"] asorti(s[,d[,m]]) sort the indices of array s, replacing the values with an integer sequence of 1 to N; if d is specified, leave the values of s intact and put the indices and sequence values into d; m is the same as for asort() 4 time_functions Builtin time functions systime() return the current time of day as the number of seconds since some reference point; on VMS the reference point is January 1, 1970, at 12 AM local time (not UTC) mktime(s) convert string s into number of seconds since the reference point; s should contain a value of the form "yyyy mm dd hh mm ss[ dst]" where yyyy is a four digit year, mm a month number from 1 to 12, dd day-of-month number from 1 to 31, hh hour 0 to 23, mm minute 0 to 59, ss second 0 to 60, and [ dst] is an optional flag to handle daylight savings time: if dst is positive, then daylight savins time is in effect, if zero, then it isn't, and if negative or omitted, gawk attempts to determine whether it was--or will be--at specified date and time strftime(f,t,u) format time value t using format f; if it is omitted then PROCINFO["strftime"] is used; if t is omitted, the default is systime(); if u is present and non-zero then t is treated as a UTC value, otherwise it is considered to be local time 5 time_formats Formatting directives similar to the 'printf' & 'sprintf' functions (each is introduced in the format string by preceding it with a percent sign (%)); the directive is substituted by the corresponding value a abbreviated weekday name (Sun,Mon,Tue,Wed,Thu,Fri,Sat) A full weekday name b abbreviated month name (Jan,Feb,...) B full month name c date and time (Unix-style "aaa bbb dd HH:MM:SS YYYY" format) C century prefix (19 or 20) [not century number, ie 20th] d day of month as two digit decimal number (01-31) D date in mm/dd/yy format e day of month with leading space instead of leading 0 ( 1-31) E ignored; following format character used H hour (24 hour clock) as two digit number (00-23) h abbreviated month name (Jan,Feb,...) [same as %b] I hour (12 hour clock) as two digit number (01-12) j day of year as three digit number (001-366) m month as two digit number (01-12) M minute as two digit number (00-59) n 'newline' (ie, treat %n as \n) O ignored; following format character used p AM/PM designation for 12 hour clock r time in AM/PM format ("II:MM:SS p") R time without seconds ("HH:MM") S second as two digit number (00-59) t tab (ie, treat %t as \t) T time ("HH:MM:SS") U week of year (00-53) [first Sunday is first day of week 1] V date (VMS-style "dd-bbb-YYYY" with 'bbb' forced to uppercase) w weekday as decimal digit (0 [Sunday] through 6 [Saturday]) W week of year (00-53) [first _Monday_ is first day of week 1] x date ("aaa bbb dd YYYY") X time ("HH:MM:SS") y year without century (00-99) Y year with century (19yy-20yy) Z time zone name (always "local" for VMS) % literal percent sign (%) 4 IO_functions Builtin I/O functions print x,... print the values of one or more expressions; if none are listed, $0 is used; parentheses are optional; when multiple values are printed, the current value of builtin OFS (default is 1 space) is used to separate them; the print line is implicitly terminated with the current value of ORS (default is newline); print does not have a return value printf(f,x,...) print the values of one or more expressions, using the specified format string; null strings are used to supply missing values (if any); no between field or trailing newline characters are printed, they should be specified within the format string; the argument-enclosing parentheses are optional; printf does not have a return value getline v read a record into variable v; if v is omitted, $0 is used (and NF, NR, and FNR are updated); if v is specified, then field-splitting won't be performed; note: parentheses around the argument are *not* allowed; return value is 1 for successful read, 0 if end of file is encountered, or -1 if some sort of error occurred; [see 'redirection' for several variants] close(s) close a file or pipe specified by the string s; the string used should have the same value as the one used in a getline or print/printf redirection fflush(s) flush output stream s; if s is omitted, stdout is flushed; if it is specified but its value is an empty string, all output streams are flushed system(s) pass string s to executed by the operating system; the command string is executed in a subprocess 5 redirection Both getline and print/printf support variant forms which use redirection and pipes. To read from a file (instead of from the primary input file), use getline var < "file" or getline < "file" (read into $0) where the string "file" represents either an actual file name (in quotes) or a variable which contains a file name string value or an expression which evaluates to a string filename. To create a pipe executing some command and read the result into a variable (or into $0), use "command" | getline var or "command" | getline (read into $0) where "command" is a literal string containing an operating system command or a variable with a string value representing such a command. To output into a file other that the primary output, use print x,... > "file" (or >> "file") or printf(f,x,...) > "file" (or >> "file") similar to the 'getline' example above. '>>' causes output to be appended to an existing file if it exists, or create the file if it doesn't already exist. '>' always creates a new file. The alternate redirection method of '>$' (for RMS text file attributes) is *only* available on the command line, not with 'print' or 'printf' in the current release. To output an error message, use 'print' or 'printf' and redirect the output to file "/dev/stderr" (or equivalently to "SYS$ERROR:" on VMS). 'stderr' will normally be the user's terminal, even if ordinary output is being redirected into a file. To feed awk output into another command, use print x,... | "command" (similarly for 'printf') similar to the second 'getline' example. In this case, output from awk will be passed as input to the specified operating system command. The command must be capable of reading input from 'stdin' ("SYS$INPUT:" on VMS) in order to receive data in this manner. The 'close' function operates on the "file" or "command" argument specified here (either a literal string or a variable or expression resulting in a string value). It completely closes the file or pipe so that further references to the same file or command string would re-open that file or command at the beginning. Closing a pipe or redirection also releases some file-oriented resources. Note: the VMS implementation of GAWK uses temporary files to simulate pipes, so a command must finish before 'getline' can get any input from it, and 'close' must be called for an output pipe before any data can be passed to the specified command. 5 formats Formatting characters used by the 'printf' and 'sprintf' functions (each is introduced in the format string by preceding it with a percent sign (%)) % include a literal percent sign (%) in the result c format the next argument as a single ASCII character (prints first character of string argument, or corresponding ASCII character if numeric argument, e.g. 65 is 'A') s format the next argument as a string (numeric arguments are converted into strings on demand) d decimal number (ie, integer value in base 10) i integer (equivalent to decimal) o octal number (integer in base 8) x hexadecimal number (integer in base 16) [lowercase] X hexadecimal number [digits 'A' thru 'E' in uppercase] f floating point number (digits, decimal point, fraction digits) e exponential (scientific notation) number (digit, decimal point, fraction digits, letter 'e', sign '+' or '-', exponent digits) g 'fractional' number in either 'e' or 'f' format, whichever produces shorter result Several optional modifiers can be placed between the initiating percent sign and the format character (doesn't apply to %%). - left justify (only matters when width specifier is present) (space) for numeric specifiers, prefix nonnegative values with a space and negative values with a minus sign + for numeric specifiers, prefix nonnegative values with a plus sign and negative values with a minus sign # alternate form applicable to several of the format characters (o, x, X, e, E, f, g, G) NN width ['NN' represents 1 or more decimal digits]; actually minimum width to use, longer items will not be truncated; a leading 0 will cause right-justified numbers to be padded on the left with zeroes instead of spaces when they're aligned .MM precision [decimal point followed by 1 or more digits]; used as maximum width for strings (causing truncation if they're actually longer) or as number of fraction digits for 'f' or 'e' numeric formats, or number of significant digits for 'g' numeric format 4 bitwise_functions Bitwise functions operate on bits (binary digits) of integer numeric values. Non-integer numbers are converted into integers before their bits are accessed. and(x,y) x AND y, where result contains 1 for bits that both x and y have set, 0 for other bits or(x,y) x OR y, where the result contains 1 for any bits that either x or y or both have set, 0 for other bits xor(x,y) x XOR y, where the result contains 1 for bits that x has set but y has clear or vice versa, 0 for other bits compl(x) NOT x, where the result contains 1 for bits that x has clear and 0 for bits that it has set lshift(x,n) x << n, shift the bits of x by n positions left, approximately the same as x * 2^n rshift(x,n) x >> n, shift the bits of x by n positions right, approximately the same as int(x / 2^n) The set of bitwise functions is a gawk extension. 4 user_defined_functions User-defined functions may be created as needed to simplify awk programs or to collect commonly used code into one place. The general syntax of a user-defined function is the 'function' keyword followed by unique function name, followed by a comma-separated parameter list enclosed in parentheses, followed by statement(s) enclosed within braces ({}). A 'return' statement is customary but is not required. function FuncName(arg1,arg2) { # arbitrary statements return (arg1 + arg2) / 2 } If a function does not use 'return' to specify an output value, the result received by the caller will be unpredictable. Functions may be placed in an awk program before, between, or after the pattern-action rules. The abbreviation 'func' may be used in place of 'function', unless POSIX compatibility mode is in effect. 4 indirect_function_calls A gawk extension allows you to assign a string containing the name of a function to a variable, then call the function by preceding the variable with @ (at-sign) and following with the parenthesized argument list. For example function my_max(x, y) { return (x > y) ? x : y } function my_min(x, y) { return (x < y) ? x : y } ... max_or_min = some_criterion ? "my_max" : "my_min" ... c = @max_or_min(a, b) would call either my_max() or my_min() depending upon the value of some_criterion at the time max_or_min was assigned. Indirect function calls only operate on user-defined functions, not on built-in ones. If you need to use one of the latter, create a user-defined function to call the built-in function; this if often referred to as a "wrapper" function. 3 regular_expressions A regular expression is a shorthand way of specifying a 'wildcard' type of string comparison. Regular expression matching is very fundamental to awk's operation. Meta symbols ^ matches beginning of line or beginning of string; note that embedded newlines ('\n') create multi-line strings, so beginning of line is not necessarily beginning of string $ matches end of line or end of string . any single character (except newline) [ ] set of characters; [ABC] matches either 'A' or 'B' or 'C'; a dash (other than first or last of the set) denotes a range of characters: [A-Z] matches any upper case letter; if the first character of the set is '^', then the sense of match is reversed: [^0-9] matches any non-digit; several characters need to be quoted with backslash (\) if they occur in a set: '\', ']', '-', and '^'; within sets, various special character class designations are recognized, such as [:digit:] and [:punct:], as per POSIX | alternation (similar to boolean 'or'); match either of two patterns [for example "^start|stop$" matches leading 'start' or trailing 'stop'] ( ) grouping, alter normal precedence [for example, "^(start|stop)$" matches lines reading either 'start' or 'stop'] * repeated matching; when placed after a pattern, indicates that the pattern should match any number of times [for example, "[a-z][0-9]*" matches a lower case letter followed by zero or more digits] + repeated matching; when placed after a pattern, indicates that the pattern should match one or more times ["[0-9]+" matches any non-empty sequence of digits] ? optional matching; indicates that the pattern can match zero or one times ["[a-z][0-9]?" matches lower case letter alone or followed by a single digit] { } interval specification; {n} to match n times or {m,n} to match at least m but not more than n times; only functional when either the `-Wposix' or `-Wre-interval' options are used \ quote; prevent the character which follows from having special meaning; if the regexp is specified as a string, then the backslash itself will need to be quoted by preceding it with another backslash A regular expression which matches a string or line will match against the first (left-most) substring which meets the pattern and include the longest sequence of characters which still meets that pattern. 3 comments Comments in awk programs are introduced with '#'. Anything after '#' on a line is ignored by GAWK. It's a good idea to include an explanation of what an awk program is doing and also who wrote it and when. 3 further_information For complete documentation on GAWK, see "Effective AWK Programming" by Arnold Robbins. The second edition (ISBN 1-57831-000-8) is jointly published by SSC and the FSF (http://www.ssc.com). Source text for it is present in the file GAWK.TEXI. A postscript version is available via anonymous FTP from host gnudist.gnu.org in directory /gnu/gawk, file gawk-{version}-doc.tar.gz where {version} would be the current version number, such as 3.0.6. Another source of documentation is "The AWK Programming Language" by Aho, Weinberger, and Kernighan (1988), published by Addison-Wesley. ISBN code is 0-201-07981-X. Each of these works contains both a reference on the awk language and a tutorial on awk's use, with many sample programs. 3 authors The awk programming language was originally created by Alfred V. Aho, Peter J. Weinberger, and Brian W. Kernighan in 1977. The language was revised and enhanced in a new version which was released in 1985. GAWK, the GNU implementation of awk, was written in 1986 by Paul Rubin and Jay Fenlason, with advice from Richard Stallman, and with contributions from John Woods. In 1988 and 1989, David Trueman and Arnold Robbins revised GAWK for compatibility with the newer awk. Arnold Robbins is the current maintainer. GAWK version 2.11.1 was ported to VMS by Pat Rankin in November, 1989, with further revisions in the Spring of 1990. The VMS port was incorporated into the official GNU distribution of version 2.13 in Spring 1991. (Version 2.12 was never publically released.) 2 release_notes GAWK 4.0.0 has many changes from 3.1.8, and these release_notes were not updated for any of the 3.1.* releases, so some information is probably missing or out of date. In particular, the known_problems subtopic hasn't been touched in many years. 3 AWK_LIBRARY GAWK uses a built in search path when looking for a program file specified by the -f option (or the /input qualifier) when that file name does not include a device and/or directory. GAWK will first look in the current default directory, then if the file wasn't found it will look in the directory specified by the translation of logical name "AWK_LIBRARY". 3 known_problems There are several known problems with GAWK running on VMS. Some can be ignored, others require work-arounds. 4 file_formats If a file having the RMS attribute "Fortran carriage control" is read as input, it will generate an empty first record if the first actual record begins with a space (leading space becomes a newline). Also, the last record of the file will give a "record not terminated" warning. Both of these minor problems are due to the way that the C Run-Time Library (VAXCRTL) converts record attributes. Another poor feature without a work-around is that there's no way to specify "append if possible, create with RMS text attributes if not" with the current command line I/O redirection. '>>$' isn't supported. Ditto for binary output; '>>+' isn't supported. 4 RS_peculiarities Changing the record separator to something other than newline ('\n') will produce anomalous results for ordinary files. For example, using RS = "\f" and FS = "\n" with the following input |rec 1, line 1 |rec 1, line 2 |^L (form feed) |rec 2, line 1 |rec 2, line 2 |^L (form feed) |rec 3, line 1 |rec 3, line 2 |(end of file) will produce two fields for record 1, but three fields each for records 2 and 3. This is because the form-feed record delimiter is on its own line, so awk sees a newline after it. Since newline is now a field separator, records 2 and 3 will have null first fields. The following awk code will work-around this problem by inserting a null first field in the first record, so that all records can be handled the same by subsequent processing. # fix up for first record (RS != "\n") FNR == 1 { if ( $0 == "" ) #leading separator next #skip its null record else #otherwise, $0 = FS $0 #realign fields } There is a second problem with this same example. It will always trigger a "record not terminated" warning when it reaches the end of file. In the sample shown, there is no final separator; however, if a trailing form-feed were present, it would produce a spurious final record with two null fields. This occurs because the I/O system sees an implicit newline at the end of the last record, so awk sees a pair of null fields separated by that newline. The following code fragment will fix that provided there are no null records (in this case, that would be two consecutive lines containing just form-feeds). # fix up for last record (RS != "\n") $0 == FS { next } #drop spurious final record Note that the "record not terminated" warning will persist. 4 cmd_inconsistency The DCL qualifier /OUTPUT is internally equivalent to '>$' output redirection, but the qualifier /INPUT corresponds to the -f option rather than to '<' input redirection. 4 exit The exit statement can optionally pass a final status value to the operating system. GAWK expects a UN*X-style value instead of a VMS status value, so 0 indicates success and non-zero indicates failure. The final exit status will be 1 (VMS success) if 0 is used, or even (VMS non-success) if non-zero is used. 3 changes Changes between version 4.0.0 and earlier versions [This 'changes' section hasn't been updated in many releases. Some features mentioned here may have become available in versions 3.1.*.] General dgawk.exe does interactive debugging of awk programs pgawk.exe does comprehensive execution profiling of awk programs -d[file] and -p[file] options added -Wcompat and -Wusage options dropped; use -Wtraditional and -Whelp BEGINFILE and ENDFILE built-in rule patterns nextfile statement skips remainder of current input file switch-case statement performs an alternate form of if-then-else indirect function calls: var="user_function"; @var(args) FPAT regexp pattern as alternative to FS field splitting patsplit() function, FPAT analog to split() PROCINFO["sorted_in"] can be used to control traversal order for 'for (index in array)' statement asort(), asorti() functions, to sort arrays sub-arrays: array element values can be arrays isarray() function, to test whether a value is an array PROCINFO["strftime"] can be used to supply default format for date/time formatting by strftime() function mktime() function, to convert list of separate date and time fields into single numeric date/time value and(), or(), xor(), compl(), lshift(), rshift() functions, to perform bit-wise logic operations on numeric values strtonum() function, to convert string of digits into number, with support for radix prefix '0' (octal) and '0x' (hexadecimal) VMS-specific New command qualifiers: /EXTRA_COMMANDS, /PROFILE, /DUMP_VARIABLES, /OPTIMIZE, /TRADITIONAL, /SANDBOX, /NON_DECIMAL_DATA Revised qualifier: /LINT, takes optional argument list Deprecated qualifier: /STRICT, superseded by /TRADITIONAL 3 prior_changes Changes between version 3.1.8 and [...] and 3.0.6 [Someday someone ought to dig up and document this information....] Changes between version 3.0.6 and 2.15.6 General RS can contain multiple characters or be a regexp Regular expression interval support added gensub() and fflush() functions added memory leak(s) introduced in 3.0.2 or 3.0.1 fixed the user manual has been substantially revised VMS-specific Switched to build with DEC C by default Changes between version 2.15.6 and 2.14 General Many obscure bugs fixed `delete' may operate on an entire array ARGIND and ERRNO builtin variables added VMS-specific `>+ file' binary-mode output redirection added /variable=(foo=42) fixed Floating point number formatting improved Changes between version 2.14 and 2.13.2: General 'next file' construct added 'continue' outside of any loop is treated as 'next' Assorted bug fixes and efficiency improvements _The_GAWK_Manual_ updated Test suite expanded VMS-specific VMS POSIX support added Disk I/O throughput enhanced Pipe emulation improved and incorrect interaction with user-mode redefinition of SYS$OUTPUT eliminated Changes between version 2.13 and 2.11.1: (2.12 was not released) General CONVFMT and FIELDWIDTHS builtin control variables added systime() and strftime() date/time functions added 'lint' and 'posix' run-time options added '-W' command line option syntax supercedes '-c', '-C', and '-V' '-a' and '-e' regular expression options made obsolete Various bug fixes and efficiency improvements More platforms supported ('officially' including VMS) VMS-specific %g printf format fixed Handling of '\' on command line modified; no longer necessary to double it up Problem redirecting stderr (>&efile) at same time as stdin (<ifile) or stdout (>ofile) has been fixed ``2>&1'' and ``1>&2'' redirection constructs added Interaction between command line I/O redirection and gawk pipes fixed; also, name used for pseudo-pipe temporary file expanded 3 license GAWK is covered by the "GNU General Public License", the gist of which is that if you supply this software to a third party, you are expressly forbidden to prevent them from supplying it to a fourth party, and if you supply binaries you must make the source code available to them at no additional cost. Any revisions or modified versions are also covered by the same license. There is no warranty, express or implied, for this software. It is provided "as is." [Disclaimer: This is just an informal summary with no legal basis; refer to the actual GNU General Public License for specific details.] !2 examples !