Changeset 2725 in MondoRescue for branches/2.2.9/mindi-busybox/shell/README


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Timestamp:
Feb 25, 2011, 9:26:54 PM (14 years ago)
Author:
Bruno Cornec
Message:
  • Update mindi-busybox to 1.18.3 to avoid problems with the tar command which is now failing on recent versions with busybox 1.7.3
File:
1 edited

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  • branches/2.2.9/mindi-busybox/shell/README

    r1765 r2725  
    1 Various bits of what is known about busybox shells, in no particular order.
     1http://www.opengroup.org/onlinepubs/9699919799/
     2Open Group Base Specifications Issue 7
    23
    3 2007-06-13
    4 hush: exec <"$1" doesn't do parameter subst
    54
    6 2007-05-24
    7 hush: environment-related memory leak plugged, with net code size
    8 decrease.
     5http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap01.html
     6Shell & Utilities
    97
    10 2007-05-24
    11 hush: '( echo ${name )' will show syntax error message, but prompt
    12 doesn't return (need to press <enter>). Pressing Ctrl-C, <enter>,
    13 '( echo ${name )' again, Ctrl-C segfaults.
     8It says that any of the standard utilities may be implemented
     9as a regular shell built-in. It gives a list of utilities which
     10are usually implemented that way (and some of them can only
     11be implemented as built-ins, like "alias"):
    1412
    15 2007-05-21
    16 hush: environment cannot be handled by libc routines as they are leaky
    17 (by API design and thus unfixable): hush will leak memory in this script,
    18 bash does not:
    19 pid=$$
    20 while true; do
    21     unset t;
    22     t=111111111111111111111111111111111111111111111111111111111111111111111111
    23     export t
    24     ps -o vsz,pid,comm | grep " $pid "
    25 done
    26 The fix is to not use setenv/putenv/unsetenv but manipulate env ourself. TODO.
    27 hush: meanwhile, first three command subst bugs mentioned below are fixed. :)
     13alias
     14bg
     15cd
     16command
     17false
     18fc
     19fg
     20getopts
     21jobs
     22kill
     23newgrp
     24pwd
     25read
     26true
     27umask
     28unalias
     29wait
    2830
    29 2007-05-06
    30 hush: more bugs spotted. Comparison with bash:
    31 bash-3.2# echo "TEST`date;echo;echo`BEST"
    32 TESTSun May  6 09:21:05 CEST 2007BEST         [we dont strip eols]
    33 bash-3.2# echo "TEST`echo '$(echo ZZ)'`BEST"
    34 TEST$(echo ZZ)BEST                            [we execute inner echo]
    35 bash-3.2# echo "TEST`echo "'"`BEST"
    36 TEST'BEST                                     [we totally mess up this one]
    37 bash-3.2# echo `sleep 5`
    38 [Ctrl-C should work, Ctrl-Z should do nothing][we totally mess up this one]
    39 bash-3.2# if true; then
    40 > [Ctrl-C]
    41 bash-3.2#                                     [we re-issue "> "]
    42 bash-3.2# if echo `sleep 5`; then
    43 > true; fi                                    [we execute sleep before "> "]
    4431
    45 2007-05-04
    46 hush: made ctrl-Z/C work correctly for "while true; do true; done"
    47 (namely, it backgrounds/interrupts entire "while")
     32http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html
     33Shell Command Language
    4834
    49 2007-05-03
    50 hush: new bug spotted: Ctrl-C on "while true; do true; done" doesn't
    51 work right:
    52 # while true; do true; done
    53 [1] 0 true <-- pressing Ctrl-C several times...
    54 [2] 0 true
    55 [3] 0 true
    56 Segmentation fault
     35It says that shell must implement special built-ins. Special built-ins
     36differ from regular ones by the fact that variable assignments
     37done on special builtin are *PRESERVED*. That is,
    5738
    58 2007-05-03
    59 hush: update on "sleep 1 | exit 3; echo $?" bug.
    60 parse_stream_outer() repeatedly calls parse_stream().
    61 parse_stream() is now fixed to stop on ';' in this example,
    62 fixing it (parse_stream_outer() will call parse_stream() 1st time,
    63 execute the parse tree, call parse_stream() 2nd time and execute the tree).
    64 But it's not the end of story.
    65 In more complex situations we _must_ parse way farther before executing.
    66 Example #2: "{ sleep 1 | exit 3; echo $?; ...few_lines... } >file".
    67 Because of redirection, we cannot execute 1st pipe before we parse it all.
    68 We probably need to learn to store $var expressions in parse tree.
    69 Debug printing of parse tree would be nice too.
     39VAR=VAL special_builtin; echo $VAR
    7040
    71 2007-04-28
    72 hush: Ctrl-C and Ctrl-Z for single NOFORK commands are working.
    73 Memory and other resource leaks (opendir) are not addressed
    74 (testcase is "rm -i" interrupted by ctrl-c).
     41should print VAL.
    7542
    76 2007-04-21
    77 hush: "sleep 5 | sleep 6" + Ctrl-Z + fg seems to work.
    78 "rm -i" + Ctrl-C, "sleep 5" + Ctrl-Z still doesn't work
    79 for SH_STANDALONE case :(
     43(Another distinction is that an error in special built-in should
     44abort the shell, but this is not such a critical difference,
     45and moreover, at least bash's "set" does not follow this rule,
     46which is even codified in autoconf configure logic now...)
    8047
    81 2007-04-21
    82 hush: fixed non-backgrounding of "sleep 1 &" and totally broken
    83 "sleep 1 | sleep 2 &". Noticed a bug where successive jobs
    84 get numbers 1,2,3 even when job #1 has exited before job# 2 is started.
    85 (bash reuses #1 in this case)
     48List of special builtins:
    8649
    87 2007-04-21
    88 hush: "sleep 1 | exit 3; echo $?" prints 0 because $? is substituted
    89 _before_ pipe gets executed!! run_list_real() already has "pipe;echo"
    90 parsed and handed to it for execution, so it sees "pipe"; "echo 0".
     50. file
     51: [argument...]
     52break [n]
     53continue [n]
     54eval [argument...]
     55exec [command [argument...]]
     56exit [n]
     57export name[=word]...
     58export -p
     59readonly name[=word]...
     60readonly -p
     61return [n]
     62set [-abCefhmnuvx] [-o option] [argument...]
     63set [+abCefhmnuvx] [+o option] [argument...]
     64set -- [argument...]
     65set -o
     66set +o
     67shift [n]
     68times
     69trap n [condition...]
     70trap [action condition...]
     71unset [-fv] name...
    9172
    92 2007-04-21
    93 hush: removed setsid() and made job control sort-of-sometimes-work.
    94 Ctrl-C in "rm -i" works now except for SH_STANDALONE case.
    95 "sleep 1 | exit 3" + "echo $?" works, "sleep 1 | exit 3; echo $?"
    96 shows exitcode 0 (should be 3). "sleep 1 | sleep 2 &" fails horribly.
     73In practice, no one uses this obscure feature - none of these builtins
     74gives any special reasons to play such dirty tricks.
    9775
    98 2007-04-14
    99 lash, hush: both do setsid() and as a result don't have ctty!
    100 Ctrl-C doesn't work for any child (try rm -i), etc...
    101 lash: bare ">file" doesn't create a file (hush works)
     76However. This section also says that *function invocation* should act
     77similar to special built-in. That is, variable assignments
     78done on function invocation should be preserved after function invocation.
     79
     80This is significant: it is not unthinkable to want to run a function
     81with some variables set to special values. But because of the above,
     82it does not work: variable will "leak" out of the function.
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