How to check if command -v $1 >/dev/null 2>&1; is false?

Question

I'm looking for a proper way to check if a command does not exist. I've read through Check if a program exists from a Bash script. So far I came up with:

command_exists () {
    command -v $1 >/dev/null 2>&1;
}

if command_exists aws; then
    echo # null
else
    brew install awscli
fi

There has to be a way to only have one if clause like:

if ! command_exists aws; then
    brew install awscli
fi

update: nevermind, above solution works.

`:` (just a colon) or `true` are better than `echo`, which has the side effect of printing a spurious line of output. — tripleee, Apr 19 '16 at 10:56
@tripleee: May be he was looking for an alternate solution unlike the one above which has a `bash` function written. — Inian, Apr 19 '16 at 10:59
@Inian Or maybe he didn't try the code, and it already works. Occam's razor would dictate my interpretation, but the question is obviously too vague, and should be updated, which only the OP can do. — tripleee, Apr 19 '16 at 11:01
I can't delete it since it has answers. I would just leave it? — mles, Apr 19 '16 at 11:04

score 3 · Accepted Answer · answered Apr 19 '16 at 10:53

3

I have a similar function defined and there’s no reason why your snippet of shell code shouldn’t work.

if ! command_exists aws; then
    brew install awscli
fi

If you prefer, you can shorten this like so:

command_exists aws || brew install awscli

answered Apr 19 '16 at 10:53

Anthony Geoghegan

1 Answers1