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| 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 -- and it doesn't even write errors to stderr! Therefore, one must parse its output. | 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. |
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| # Another easy way in gnu: if [ -z "$(which qwerty)" ]; then |
# Another easy way that works only on gnu: if ! which qwerty 2>/dev/null; then |
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| (Also note that its output is ''not'' consistent across platforms. On HP-UX, for example, it prints {{{no qwerty in /path /path /path ...}}}; on OpenBSD, it prints {{{qwerty: Command not found.}}}; and on GNU/Linux, it prints nothing at all.) | (Also note that its output is ''not'' consistent across platforms. On HP-UX, for example, it prints {{{no qwerty in /path /path /path ...}}}; on OpenBSD, it prints {{{qwerty: Command not found.}}}; and on Debian and Suse, it prints nothing at all. On Gentoo, it actually prints something to stderr.) |
How can I determine whether a command exists anywhere in my PATH?
In BASH, there are a couple builtins that are suitable for this purpose: hash and type. Here's an example using hash:
if hash qwerty 2>/dev/null; then echo qwerty exists else echo qwerty does not exist fi
If these builtins are not available (because you're in a Bourne shell, or whatever), then you may have to rely on the external command which (which is often a csh script, although sometimes a compiled binary). Unfortunately, which does not set a useful exit code (on any system but GNU/Linux) -- and it doesn't even write errors to stderr! Therefore, one must parse its output.
# Last resort -- using which(1) x=$(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
# Another easy way that works only on gnu: if ! which qwerty 2>/dev/null; then echo "$0: install qwerty first" exit 1 fi
(Also 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.; and on Debian and Suse, it prints nothing at all. On Gentoo, it actually prints something to stderr.)