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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}}} does ''not'' set a useful exit code (on any system but GNU/Linux) -- and it doesn't even write errors to stderr! Therefore, one must parse its output. {{{ # Last resort -- using which(1) # Backticks here because we're assuming a legacy Bourne shell. x=`LC_ALL=C which qwerty 2>&1` case "$x" in no\ *\ in\ *) echo qwerty does not exist;; *Command\ not\ found.) echo qwerty does not exist;; '') echo qwerty does not exist;; *) echo qwerty exists;; esac }}} 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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