which is non-standard. Use builtin command -v instead.
This is an optional suggestion. It must be explicitly enabled with a directive enable=deprecate-which in a # shellcheck comment or .shellcheckrc
Problematic code:
which grep
Correct code:
# For the path of a single, unaliased, external command,
# or to check whether this will just "run" in this shell:
command -v grep
# To check whether commands exist, without obtaining a reusable path:
hash grep
Rationale:
which is a non-standard, external tool that locates an executable in PATH. command -v is a POSIX standard builtin, which uses the same lookup mechanism that the shell itself would.
Exceptions:
This check is opt-in only in 0.7.1+, and you may choose to ignore it in earlier versions. which is very common, and some prefer its executable-or-nothing behavior over command -v's handling of builtins, functions and aliases.
Caveats:
command -v does not check ALL parameters
command -v succeeds (with exit code 0) if any command exists:
# grep is in /usr/bin/grep
# foobar is not in path
#
$ command -v -- grep foobar; echo $?
0
In the above example, it should have failed and exited with 1 unless all commands
exist, if it were to be a replacement for which. Other problems associated with
command include its inclusion of builtins, aliases, and functions.
An alternative is:
$ hash <file1> <file2>
Which observes the standard behaviour of failures.
To obtain a path, type -p can be used instead. Like command -v, it has a similarly
quirky behavior with builtins, aliases, and functions, although this is
arguably milder since it would print nothing for these cases. The failure condition is
similar to hash.
Related resources:
shellcheckissue: #1162 command -v is not a direct replacement for which (Discussion)- Check if a program exists from a Bash script on StackOverflow.
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Installation
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Usage
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Integrating and extending
Each individual ShellCheck warning has its own wiki page like SC1000. Use GitHub Wiki's "Pages" feature above to find a specific one, or see Checks.