Re: Absolute pathnames to commands in shell scripts
From: Stephane CHAZELAS (this.address_at_is.invalid)
Date: 01/30/04
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Date: Fri, 30 Jan 2004 01:45:12 +0100
2004-01-29, 18:35(+01), Stephane CHAZELAS:
[...]
> IFS is not a problem. Depending on the shell/the script there
> may be with ENV, BASH_ENV, FIGNORE, SHELLOPTS, ARGV0, HOME,
> ZDOTDIR, FPATH, LANG, LC_*, TMOUT (funny with bash and ksh93),
> LD_PRELOAD, SHLIB_PATH, LD_LIBRARY_PATH, all sorts of other
> dynamic linker variables, STTY, TMPPREFIX... some of which you
> can't do anything against (as it's too late when the script is
> started).
[...]
some precisions:
IFS:
affects: very early Bourne shells (others ignore the IFS
variable found in there environment on startup)
effect: on those shells, syntax parsing, word splitting...
example:
$ IFS=i sh -c exit
runs "ex" on the "t" file.
ENV:
affects: pdksh, ksh88, zsh in sh or ksh emulation, some shells
based on ash.
effect: sources the given script, command substitution expanded
in ENV value. If the value expands to the path of a fifo, the
shell is blocked.
example:
$ ENV='$(echo foo >&2)' ksh -c :
foo
BASH_ENV:
affects: bash
effect: same as above
FIGNORE:
affects: ksh93
effect: change the filename generation behavior
example:
$ FIGNORE='!(..)' ksh93 -c 'echo rm -rf *.*'
rm -rf ..
SHELLOPTS:
affects: bash
effect: change the shell options
example:
$ SHELLOPTS=noexec:verbose bash -c 'echo foo'
echo foo
ARGV0:
affects: zsh
effect: changes the emulation mode
example:
$ ARGV0=csh zsh -c 'a=/et*; echo "$a"'
/etc
HOME:
affects: zsh
effect: it's the place where ".zshenv" file is found if $ZDOTDIR
is not set.
$ echo echo foo > /tmp/.zshenv
$ HOME=/tmp zsh -c :
foo
ZDOTDIR:
affects: zsh
effect: see above
FPATH:
affects: zsh, ksh
effect: same as PATH except that's for library functions
example:
$ echo echo foo > /tmp/zmv
$ FPATH=/tmp zsh -c 'autoload zmv; zmv a b'
foo
LANG, LC_...:
affects: most modern shells, ksh93 badly
effect: changes the sort order, the charset/language used for
messages, the displayed time format, the "ls -l" output format,
the numeric format (breaks ksh93 script that use floating point
arithmetic)...
example:
$ date +%B
January
$ LC_TIME=fr sh -c '[ "$(date +%B)" = January ] || echo We are not in January'
We are not in January
$ LC_NUMERIC=fr_FR ksh93 -c 'echo $((3.14159))'
ksh93: line 1: 3.14159: arithmetic syntax error
TMOUT:
affects: bash, ksh93
effect: "read" fails if it takes more than $TMOUT to perform
example:
$ TMOUT=1 ksh93 -c '(sleep 2; echo a) | (read a; echo b$a)'
b
TMOUT, PPID, HISTCMD, MAILCHECK, LINENO, OPTIND, RANDOM, SECONDS...
affects: ksh93, pdksh for some
effect: ksh93 returns immediately with an error if the value is
not a valid arithmetic expression.
example:
$ RANDOM=++ ksh93 -c 'echo foo'
ksh93: ++: more tokens expected
LD_PRELOAD, LD_LIBRARY_PATH...
affects: every non statically linked shell
effect: shells rely on functions from libc or other libraries,
they can be replaced by other ones this way. Other side effects,
with other variables, depending on the system.
example:
$ LD_TRACE_LOADED_OBJECTS=1 sh -c :
libdl.so.2 => /lib/libdl.so.2 (0x40021000)
libc.so.6 => /lib/libc.so.6 (0x40024000)
/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)
STTY:
affects: zsh
effect: change the terminal settings (runs stty before each
command)
example:
$ STTY=-g zsh -c :
500:5:bf:8a3b:3:1c:8:15:4:0:1:0:11:13:1a:0:12:f:17:16:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0
TMPPREFIX:
affects: zsh
effect: change the path where temporary files are created (for
here documents/strings and =(...))
example:
$ TMPPREFIX=/ zsh -c 'cat <<< foo'
zsh: permission denied
TMPDIR:
affects: pdksh
effect: same as above, except that pdksh reverts to the system
default tmp dir if it is unable to create a tmpfile in $TMPDIR
(but it may still fail for file paths too long for instance).
OPTIND:
affects: zsh (a bug)
effect: getopts fails
example:
$ OPTIND=4 zsh -c 'getopts a var -a; echo "<$var>"'
<>
PS4:
affects: most shells
effect: change the display for xtracing, and command
substitution is performed.
$ PS4='$(()' pdksh -cx :
pdksh: no closing quote
EXECSHELL:
affects: pdksh
effects: command used to run command that return ENOEXEC (valid
scripts without a shebang)
example:
$ echo echo b > a; chmod +x a
$ EXECSHELL=echo pdksh -c ./a
./a
POSIXLY_CORRECT:
affects: pdksh,
CDPATH:
affects: most recent shells
effect: cd'ing to a directory may no longer fail, cd may output
unexpected strings.
example:
$ mkdir /tmp/A /tmp/B
$ cd /tmp/B
$ CDPATH=/tmp bash -c 'cd A && pwd'
/tmp/A
/tmp/A
PATH:
affects: every shell
effect: well known
That list is probably not exhaustive.
-- Stéphane ["Stephane.Chazelas" at "free.fr"]
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