Check if a command exists in POSIX sh

Check that a command exists with command -v in POSIX sh. It is a builtin, it sees functions and builtins, and which does not.

1 min read

Summarize in AI

Before using a tool, a script wants to know whether it is installed, and the answer should be the same in dash, Bash and BusyBox.

Shell

for c in git nosuchtool; do
  if command -v "$c" >/dev/null 2>&1; then
    echo "$c: found"
  else
    echo "$c: missing"
  fi
done
command -v cd
which cd
echo "which exit status: $?"

Text

git: found
nosuchtool: missing
cd
which exit status: 1

command -v name prints how the shell would resolve the name and exits non-zero when it cannot. It is specified in POSIX, runs inside the shell, and knows about builtins, functions and aliases. which is a separate program whose output and exit status differ between systems, and it cannot see a builtin, as the last two lines show.

command -v answers whether the shell can run the name, not whether it is the tool you expect. A function named git makes it succeed, so check the path with command -v git when that matters.

Taggedportability posix scripting sh

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