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| -rw-r--r-- | shell/README | 190 |
1 files changed, 82 insertions, 108 deletions
diff --git a/shell/README b/shell/README index 59efe499f..550c712d3 100644 --- a/shell/README +++ b/shell/README @@ -1,108 +1,82 @@ -Various bits of what is known about busybox shells, in no particular order. - -2008-02-14 -ash: does not restore tty pgrp if killed by HUP. Symptom: Midnight Commander -is backgrounded if you started ash under it, and then killed it with HUP. - -2007-11-23 -hush: fixed bogus glob handling; fixed exec <"$1"; added test and echo builtins - -2007-06-13 -hush: exec <"$1" doesn't do parameter subst - -2007-05-24 -hush: environment-related memory leak plugged, with net code size -decrease. - -2007-05-24 -hush: '( echo ${name )' will show syntax error message, but prompt -doesn't return (need to press <enter>). Pressing Ctrl-C, <enter>, -'( echo ${name )' again, Ctrl-C segfaults. - -2007-05-21 -hush: environment cannot be handled by libc routines as they are leaky -(by API design and thus unfixable): hush will leak memory in this script, -bash does not: -pid=$$ -while true; do - unset t; - t=111111111111111111111111111111111111111111111111111111111111111111111111 - export t - ps -o vsz,pid,comm | grep " $pid " -done -The fix is to not use setenv/putenv/unsetenv but manipulate env ourself. TODO. -hush: meanwhile, first three command subst bugs mentioned below are fixed. :) - -2007-05-06 -hush: more bugs spotted. Comparison with bash: -bash-3.2# echo "TEST`date;echo;echo`BEST" -TESTSun May 6 09:21:05 CEST 2007BEST [we dont strip eols] -bash-3.2# echo "TEST`echo '$(echo ZZ)'`BEST" -TEST$(echo ZZ)BEST [we execute inner echo] -bash-3.2# echo "TEST`echo "'"`BEST" -TEST'BEST [we totally mess up this one] -bash-3.2# echo `sleep 5` -[Ctrl-C should work, Ctrl-Z should do nothing][we totally mess up this one] -bash-3.2# if true; then -> [Ctrl-C] -bash-3.2# [we re-issue "> "] -bash-3.2# if echo `sleep 5`; then -> true; fi [we execute sleep before "> "] - -2007-05-04 -hush: made ctrl-Z/C work correctly for "while true; do true; done" -(namely, it backgrounds/interrupts entire "while") - -2007-05-03 -hush: new bug spotted: Ctrl-C on "while true; do true; done" doesn't -work right: -# while true; do true; done -[1] 0 true <-- pressing Ctrl-C several times... -[2] 0 true -[3] 0 true -Segmentation fault - -2007-05-03 -hush: update on "sleep 1 | exit 3; echo $?" bug. -parse_stream_outer() repeatedly calls parse_stream(). -parse_stream() is now fixed to stop on ';' in this example, -fixing it (parse_stream_outer() will call parse_stream() 1st time, -execute the parse tree, call parse_stream() 2nd time and execute the tree). -But it's not the end of story. -In more complex situations we _must_ parse way farther before executing. -Example #2: "{ sleep 1 | exit 3; echo $?; ...few_lines... } >file". -Because of redirection, we cannot execute 1st pipe before we parse it all. -We probably need to learn to store $var expressions in parse tree. -Debug printing of parse tree would be nice too. - -2007-04-28 -hush: Ctrl-C and Ctrl-Z for single NOFORK commands are working. -Memory and other resource leaks (opendir) are not addressed -(testcase is "rm -i" interrupted by ctrl-c). - -2007-04-21 -hush: "sleep 5 | sleep 6" + Ctrl-Z + fg seems to work. -"rm -i" + Ctrl-C, "sleep 5" + Ctrl-Z still doesn't work -for SH_STANDALONE case :( - -2007-04-21 -hush: fixed non-backgrounding of "sleep 1 &" and totally broken -"sleep 1 | sleep 2 &". Noticed a bug where successive jobs -get numbers 1,2,3 even when job #1 has exited before job# 2 is started. -(bash reuses #1 in this case) - -2007-04-21 -hush: "sleep 1 | exit 3; echo $?" prints 0 because $? is substituted -_before_ pipe gets executed!! run_list_real() already has "pipe;echo" -parsed and handed to it for execution, so it sees "pipe"; "echo 0". - -2007-04-21 -hush: removed setsid() and made job control sort-of-sometimes-work. -Ctrl-C in "rm -i" works now except for SH_STANDALONE case. -"sleep 1 | exit 3" + "echo $?" works, "sleep 1 | exit 3; echo $?" -shows exitcode 0 (should be 3). "sleep 1 | sleep 2 &" fails horribly. - -2007-04-14 -lash, hush: both do setsid() and as a result don't have ctty! -Ctrl-C doesn't work for any child (try rm -i), etc... -lash: bare ">file" doesn't create a file (hush works) +http://www.opengroup.org/onlinepubs/9699919799/ +Open Group Base Specifications Issue 7 + + +http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap01.html +Shell & Utilities + +It says that any of the standard utilities may be implemented +as a regular shell built-in. It gives a list of utilities which +are usually implemented that way (and some of them can only +be implemented as built-ins, like "alias"): + +alias +bg +cd +command +false +fc +fg +getopts +jobs +kill +newgrp +pwd +read +true +umask +unalias +wait + + +http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html +Shell Command Language + +It says that shell must implement special built-ins. Special built-ins +differ from regular ones by the fact that variable assignments +done on special builtin is *PRESERVED*. That is, + +VAR=VAL special_builtin; echo $VAR + +should print VAL. + +(Another distinction is that an error in special built-in should +abort the shell, but this is not such a critical difference, +and moreover, at least bash's "set" does not follow this rule, +which is even codified in autoconf now...). + +List of special builtins: + +. file +: [argument...] +break [n] +continue [n] +eval [argument...] +exec [command [argument...]] +exit [n] +export name[=word]... +export -p +readonly name[=word]... +readonly -p +return [n] +set [-abCefhmnuvx] [-o option] [argument...] +set [+abCefhmnuvx] [+o option] [argument...] +set -- [argument...] +set -o +set +o +shift [n] +times +trap n [condition...] +trap [action condition...] +unset [-fv] name... + +In practice, no one uses this obscure feature - none of these builtins +gives any special reasons to play such dirty tricks. + +However. This section says that *function invocation* should act +similar to special built-in. That is, variable assignments +done on function invocation should be preserved after function invocation. + +This is significant: it is not unthinkable to want to run a function +with some variables set to special values. But because of the above, +it does not work: variable will "leak" out of the function. |