CODEWITHSUNDEEP
bashshell
Justin M. Keyes
Justin M. Keyes

Reputation: 6964

Test whether a command option is supported

In my .bashrc, I want to alias grep to grep --color if the --color option is supported. But --color isn't supported on old systems like msysgit:

$ grep --color
grep: unrecognized option '--color'
$ grep --version
grep (GNU grep) 2.4.2

In .bashrc, how can I determine whether an option is supported? I can test for a hard-coded version number, but that will break for versions >2.5:

if [[ `grep --version` == *2.5* ]] ; then
    alias grep='grep --color=auto'
fi

Is there a more reliable way to test if a command supports an option?

Upvotes: 5

Views: 1121

Answers (2)

cmh
cmh

Reputation: 10937

Take a grep command which you know will succeed and add the color option E.g.

grep --color "a" <<< "a"

the return code will be 0 if the option exists, and positive otherwise.

So your bashrc will look like:

if grep --color "a" <<<"a" &>/dev/null; then
    alias grep='grep --color=auto'
fi

&> sends stdout and stderr to /dev/null, so if the command fails, it is silenced. But it still returns an error code, which prevents the alias from being set.

Upvotes: 9

tohava
tohava

Reputation: 5412

`
echo s > dummy ;
grep --color s dummy ;
if [[ $? == 2 ]]; then
    echo not supported
fi
`

Upvotes: 0

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