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bin/ksh/NOTES
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jca
Some more tweaks to NOTES
12 янв 2018, 17:20
12 янв 2018, 17:20
10224b2
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$OpenBSD: NOTES,v 1.16 2018/01/12 14:20:57 jca Exp $ General features of at&t ksh88 that are not (yet) in pdksh: - exported aliases and functions (not in ksh93). - set -t. - signals/traps not cleared during functions. - trap DEBUG, local ERR and EXIT traps in functions. - ERRNO parameter. - read/select aren't hooked in to the command line editor - the last command of a pipeline is not run in the parent shell Known bugs (see also PROJECTS files): Variable parsing, Expansion: - some specials behave differently when unset (eg, IFS behaves like " \t\n") others lose their special meaning. IFS/PATH taken care of, still need to sort out some others (eg, TMOUT). Parsing,Lexing: - line numbers in errors are wrong for nested constructs. Need to keep track of the line a command started on (can use for LINENO parameter as well). - a $(..) expression nested inside double quotes inside another $(..) isn't parsed correctly (eg, $(echo "foo$(echo ")")") ) Commands,Execution: - setting special parameters that have side effects when changed/restored (ie, HISTFILE, OPTIND, RANDOM) in front of a command (eg, HISTFILE=/foo/bar echo hi) affects the parent shell. Note that setting other (not so special) parameters does not affect the parent shell. - `echo hi | exec cat -n' causes at&t to exit, `exec echo hi | cat -n' does not. pdksh exits for neither. Don't think POSIX requires an exit, but not sure. - `echo foo | read bar; echo $bar' prints foo in at&t ksh, nothing in pdksh (ie, the read is done in a separate process in pdksh). Known problems not caused by ksh: - after stoping a job, emacs/vi is not re-entered. Hitting return prints the prompt and everything is fine again. Problem (often involving a pager like less) is related to order of process scheduling (shell runs before `stop'ed (sub) processes have had a chance to clean up the screen/terminal). Known differences between pdksh & at&t ksh (that may change) - vi: - `^U': at&t: kills only what has been inserted, pdksh: kills to start of line - at&t ksh login shells say "Warning: you have running jobs" if you try to exit when there are running jobs. An immediate second attempt to exit will kill the jobs and exit. pdksh does not print a warning, nor does it kill running jobs when it exits (it does warn/kill for stopped jobs). - TMOUT: at&t prints warning, then waits another 60 seconds. If on screwed up serial line, the output could cause more input, so pdksh just prints a message and exits. (Also, in at&t ksh, setting TMOUT has no effect after the sequence "TMOUT=60; unset TMOUT", which could be useful - pdksh may do this in the future). - in pdksh, if the last command of a pipeline is a shell builtin, it is not executed in the parent shell, so "echo a b | read foo bar" does not set foo and bar in the parent shell (at&t ksh will). This may get fixed in the future, but it may take a while. - in pdksh, set +o lists the options that are currently set, in at&t ksh it is the same as set -o. - in pdksh emacs mode, ^T does what gnu emacs does, not what at&t ksh does. - in ksh93, `. name' calls a function (defined with function) with POSIX semantics (instead of ksh semantics). in pdksh, . does not call functions. - test: "test -f foo bar blah" is the same as "test -f foo" (the extra arguments, of which there must be at least 2, are ignored) - pdksh generates an error message (unexpected operator/operand "bar") as it should. Sometimes used to test file globs (e.g., if test -f *.o; ...). - if the command 'sleep 5 && /bin/echo blah' is run interactively and is the sleep is stopped (^Z), the echo is run immediately in pdksh. In at&t ksh, the whole thing is stopped. - LINENO: - in ksh88 variable is always 1 (can't be changed) in interac mode; in pdksh it changes. - Value of LINENO after it has been set by the script in one file is bizarre when used in another file. Known differences between pdksh & at&t ksh (that are not likely to change) - at&t ksh seems to catch or ignore SIGALRM - pdksh dies upon receipt (unless it's traped of course) - typeset: - at&t ksh overloads -u/-l options: for integers, means unsigned/long, for strings means uppercase/lowercase; pdksh just has the upper/lower case (which can be useful for integers when base > 10). unsigned/long really should have their own options. - at&t ksh can't have justified integer variables (eg, typeset -iR5 j=10), pdksh can. - in pdksh, number arguments for -L/-R/-Z/-i must follow the option character, at&t allows it at the end of the option group (eg, at&t ksh likes "typeset -iu5 j", pdksh wants "typeset -i5 -u j" or "typeset -ui5 j"). Also, pdksh allows "typeset -i 5 j" (same as "typeset -i5 j"), at&t ksh does not allow this. - typeset -R: pdksh strips trailing space type characters (ie, uses isspace()), at&t ksh only skips blanks. - at&t ksh allows attributes of read-only variables to be changed, pdksh allows only the export attribute to be set. - (some) at&t ksh allows set -A of readonly variables, pdksh does not. - at&t ksh allows command assignments of readonly variables (eg, YY=2 cat), pdksh does not. - at&t ksh does not exit scripts when an implicit assignment to an integer variable fails due to an expression error: eg, echo 2+ > /tmp/x unset x; typeset -i x read x < /tmp/x echo still here prints an error and then prints "still here", similarly for unset x; typeset -i x set +A x 1 2+ 3 echo still here and unset x y; typeset -i x y; set +A y 10 20 30 set +A x 1 1+y[2+] 3 echo still here pdksh exits a script in all the above cases. (note that both shells exit for: unset x; typeset -i x for x in 1 2+ 3; do echo x=$x; done echo still here ). - at&t ksh seems to allow function calls inside expressions (eg, typeset -i x='y(2)') but they do not seem to be regular functions nor math functions (eg, pow, exp) - anyone known anything about this? - `set -o nounset; unset foo; echo ${#foo}`: at&t ksh prints 0; pdksh generates error. Same for ${#foo[*]} and ${#foo[@]}. - . file: at&t ksh parses the whole file before executing anything, pdksh executes as it parses. This means aliases defined in the file will affect how pdksh parses the file, but won't affect how at&t ksh parses the file. Also means pdksh will not parse statements occurring after a (executed) return statement. - a return in $ENV in at&t ksh will cause the shell to exit, while in pdksh it will stop executing the script (this is consistent with what a return in .profile does in both shells). - at&t ksh does file globbing for `echo "${foo:-"*"}"`, pdksh does not (POSIX would seem to indicate pdksh is right). - at&t ksh thinks ${a:##foo} is ok, pdksh doesn't. - at&t does tilde expansion on here-document delimiters, pdksh does not. eg. $ cat << ~michael ~michael $ works for pdksh, not for at&t ksh (POSIX seems to agree with pdksh). - in at&t ksh, tracked aliases have the export flag implicitly set and tracked aliases and normal aliases live in the same name space (eg, "alias" will list both tracked and normal aliases). in pdksh, -t does not imply -x (since -x doesn't do anything yet), and tracked/normal aliases live in separate name spaces. in at&t ksh, alias accepts + options (eg, +x, +t) - pdksh does not. in pdksh, alias has a -d option to allow examination/changing of cached ~ entries, also unalias has -d and -t options (unalias -d is useful if the ~ cache gets out of date - not sure how at&t deals with this problem (it does cache ~ entries)). - at&t ksh will stop a recursive function after about 60 calls; pdksh will not since the limit is arbitrary and can't be controlled by the user (hit ^C if you get in trouble). - the wait command (with and without arguments) in at&t ksh will wait for stopped jobs when job control is enabled. pdksh doesn't. - at&t ksh automatically sets the bgnice option for interactive shells; pdksh does not. - in at&t ksh, "eval `false`; echo $?" prints 1, pdksh prints 0 (which is what POSIX says it should). Same goes for "wait `false`; echo $?". (same goes for "set `false`; echo $?" if posix option is set - some scripts that use the old getopt depend on this, so be careful about setting the posix option). - in at&t ksh, print -uX and read -uX are interrperted as -u with no argument (defaults to 1 and 0 respectively) and -X (which may or may not be a valid flag). In pdksh, -uX is interpreted as file descriptor X. - in at&t ksh, some signals (HUP, INT, QUIT) cause the read to exit, others (ie, everything else) do not. When it does cause exiting, anything read to that point is used (usually an empty line) and read returns with 0 status. pdksh currently does similar things, but for TERM as well and the exit status is 128+<signal-number> - in future, pdksh's read will do this for all signals that are normally fatal as required by POSIX. (POSIX does not require the setting of variables to null so applications shouldn't rely on this). - in pdksh, ! substitution done before variable substitution; in at&t ksh it is done after substitution (and therefore may do ! substitutions on the result of variable substitutions). POSIX doesn't say which is to be done. - pwd: in at&t ksh, it ignores arguments; in pdksh, it complains when given arguments. - the at&t ksh does not do command substition on PS1, pdksh does. - ksh93 allows ". foo" to run the function foo if there is no file called foo (go figure). - field splitting (IFS): ksh88/ksh93 strip leading non-white space IFS chars, pdksh (and POSIX, I think) leave them intact. e.g. $ IFS="$IFS:"; read x; echo "<$x>" :: prints "<>" in at&t ksh, "<::>" in pdksh. - command completion: at&t ksh will do completion on a blank line (matching all commands), pdksh does not (as this isn't very useful - use * if you really want the list). - co-processes: if ksh93, the write portion of the co-process output is closed when the most recently started co-process exits. pdksh closes it when all the co-processes using it have exited. - pdksh accepts empty command lists for while and for statements, while at&t ksh (and sh) don't. Eg., pdksh likes while false ; do done but ksh88 doesn't like it. - pdksh bumps RANDOM in parent after a fork, at&t ksh bumps it in both parent and child: RANDOM=1 echo child: `echo $RANDOM` echo parent: $RANDOM will produce "child: 16838 parent: 5758" in pdksh, while at&t ksh will produce "child: 5758 parent: 5758". Oddities in ksh (pd & at&t): - array references inside (())/$(()) are strange: $(( x[2] )) does the expected, $(( $x[2] )) doesn't. - `typeset -R3 X='x '; echo "($X)"` produces ( x) - trailing spaces are stripped. - typeset -R turns off Z flag. - both shells have the following mis-feature: $ x='function xx { cat -n <<- EOF here we are in xx EOF }' $ (eval "$x"; (sleep 2; xx) & echo bye) [1] 1234 bye $ xx: /tmp/sh1234.1: cannot open - bizarre special handling of alias/export/readonly/typeset arguments $ touch a=a; typeset a=[ab]; echo "$a" a=[ab] $ x=typeset; $x a=[ab]; echo "$a" a=a $ - both ignore SIGTSTP,SIGTTIN,SIGTTOU in exec'd processes when talking and not monitoring (at&t ksh kind of does this). Doesn't really make sense. (Note that ksh.att -ic 'set +m; check-sigs' shows TSTP et al aren't ignored, while ksh.att -ic 'set +m^J check-sigs' does... very strange) - when tracing (set -x), and a command's stderr is redirected, the trace output is also redirected. so "set -x; echo foo 2> /tmp/O > /dev/null" will create /tmp/foo with the lines "+ > /dev/null" and "+ echo foo". - undocumented at&t ksh88, documented in ksh93: FPATH is searched after PATH if no executable is found, even if typeset -uf wasn't used. POSIX sh questions (references are to POSIX 1003.2-1992) - arithmetic expressions: how are empty expressions treated? (eg, echo $(( ))). at&t ksh (and now pdksh) echo 0. Same question goes for `test "" -eq 0' - does this generate an error or, if not, what is the exit code? - if a signal is received during the execution of a built-in, does the builtin command exit or the whole shell? - is it legal to execute last command of pipeline in current execution environment (eg, can "echo foo | read bar" set bar?) - what action should be taken if there is an error doing a dup due to system limits (eg, not enough file destriptors): is this a "redirection error" (in which case a script will exit iff the error occured while executing a special built-in)? IMHO, shell should exit script. Couldn't find a blanket statement like "if shell encounters an unexpected system error, it shall exit non-interactive scripts"... POSIX sh bugs (references are to POSIX 1003.2-1992) - in vi insert mode, ^W deletes to beginning of line or to the first blank/punct character (para at line 9124, section 3). This means "foo ^W" will do nothing. This is inconsistent with the vi spec, which says delete preceding word including and interceding blanks (para at line 5189, section 5). - parameter expansion, section 3.6.2, line 391: `in each case that a value of word is needed (..), word shall be subjected to tilde expansion, parameter expansion, ...'. Various expansions should not be performed if parameter is in double quotes. - the getopts description says assigning OPTIND a value other than 1 produces undefined results, while the rationale for getopts suggests saving/restoring the OPTIND value inside functions (since POSIX functions don't do the save/restore automatically). Restoring OPTIND is kind of dumb since getopts may have been in the middle of parsing a group of flags (eg, -abc). - `...` definition (3.6.3) says nothing about backslash followed by a newline, which sh and at&t ksh strip out completely. e.g., $ show-args `echo 'X Y'` Number of args: 1 1: <XY> $ POSIX would indicate the backslash-newline would be preserved. - does not say how "cat << ''" is to be treated (illegal, read 'til blank line, or read 'til eof). at&t ksh reads til eof, bourne shell reads 'til blank line. pdksh reads 'til blank line.