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Comment: which : change to use verb "may". E.g. under Solaris, which does set proper exit code and write message to sderr. New Which() function
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| [[Anchor(faq81)]] == How can I determine whether a command exists anywhere in my PATH? == In BASH, there are a couple builtins that are suitable for this purpose: {{{hash}}} and {{{type}}}. Here's an example using {{{hash}}}: {{{ if hash qwerty 2>/dev/null; then echo qwerty exists else echo qwerty does not exist fi }}} If these builtins are not available (because you're in a Bourne shell, or whatever), then you may have to rely on the external command {{{which}}} (which is often a csh script, although sometimes a compiled binary). Unfortunately, {{{which}}} may no set a useful ''exit'' ''code'' on systems other than GNU/Linux -- and it may not even write errors to stderr. In those cases, one must parse its output. {{{ # Last resort -- using which(1) # Backticks + unset (no "local" used for variable); assume a legacy Bourne shell. function Which() { [ "$1" ] || return 1 # Require ARG tmpval=`LC_ALL=C which $1 2>&1` case "$tmpval" in *no\ *\ in\ *) tmpval="" ;; *not\ found*) tmpval="" ;; '') tmpval="" ;; esac if [ "$tmpval" ]; then echo $tmpval unset tmpval # prevent variable leak from function return 0 else unset tmpval return 1 fi } Which which }}} Note that its output is ''not'' consistent across platforms. On HP-UX, for example, it prints {{{no qwerty in /path /path /path ...}}}; on OpenBSD, it prints {{{qwerty: Command not found.}}}; on Debian and SuSE, it prints nothing at all; and on Gentoo, it actually prints something to stderr. {{{ # Another easy way that works only on gnu: if ! which qwerty >/dev/null 2>&1; then echo "$0: install qwerty first" exit 1 fi }}} (Although, on a GNU system, one would generally prefer to use one of the Bash builtins instead.) |
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