Bash command check if string match in command output

Question

I have following command output

$ /opt/CrowdStrike/falconctl -g --aid | grep 'aid='
aid="fdwe234wfgrgf34tfsf23rwefwef3".

I want to check if there is any string after aid= (inside ""). If there is any string, command return code should be 0 and if no value return code must be !=0.

Can someone please help to extend this command to get required output?

Idea is to make sure my bash script to fail if aid= doesn't has any value.

You could use grep -q, which has exactly the exit status behaviour you describe: falconctl -g aid | grep -q 'aid="[^"]*YOURSTRING[^"]*"' — Benjamin W.
– Benjamin W., Commented Dec 22, 2022 at 17:38
Or are you looking for "not empty", and not a specific string? — Benjamin W.
– Benjamin W., Commented Dec 22, 2022 at 17:38
falconctl ... | grep -q 'aid="..*"' might be what you want. — M. Nejat Aydin
– M. Nejat Aydin, Commented Dec 22, 2022 at 17:52
could you update the question to show an example of what 'no value' looks like ... aid=""? aid=? something else? — markp-fuso
– markp-fuso, Commented Dec 22, 2022 at 18:22
@hlesnt395h It matches if there is at least one character enclosed in double quotes. — M. Nejat Aydin
– M. Nejat Aydin, Commented Dec 23, 2022 at 12:23

Stephen Quan · Accepted Answer · 2022-12-22 22:54:57Z

2

You can use regex to check whether one or more characters exist inside the double quotes. And, you can use regex capture group to extract that value:

if [[ $(/opt/CrowdStrike/falconctl -g --aid | grep 'aid=') =~ ^aid=\"(.+)\"$ ]]; then
  aid=${BASH_REMATCH[0]}
  echo "aid is $aid"
else
  echo "aid not found"
fi

Note that the regex I use is .+ which means 1 or more characters, since you require the string to be non-empty. This is in contrast of the usual .* regex which would have be 0 or more characters.

answered Dec 22, 2022 at 22:54

Stephen Quan

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Comments

markp-fuso · Accepted Answer · 2022-12-22 17:54:32Z

1

I don't have falconctl on my system so to mimic its output I'll use a couple files:

$ head falcon*out
==> falcon.1.out <==
some stuff
aid="fdwe234wfgrgf34tfsf23rwefwef3".
some more stuff

==> falcon.2.out <==
some stuff
aid=""
some more stuff

One grep idea:

grep -Eq '^aid="[^"]+"' <filename>

Where:

-E - enable extended regex support
-q - run in silent/quiet mode (suppress all output)
the return code can be captured from $?

Taking for a test drive:

for fname in falcon*out
do
    printf "\n############# %s\n" "$fname"
    cat "$fname" | grep -Eq '^aid="[^"]+"' "$fname"
    echo "return code: $?"
done

This generates:

############# falcon.1.out
return code: 0

############# falcon.2.out
return code: 1

answered Dec 22, 2022 at 17:54

markp-fuso

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1 Comment

hlesnt395 Over a year ago

Thanks a lot for your reply. Let me try this out and come back here.

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