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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 -- 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
}}}

(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.)
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BashFAQ/081 (last edited 2023-05-22 10:02:19 by emanuele6)