Bash checking if string does not contain other string

Question

I have a string ${testmystring} in my .sh script and I want to check if this string does not contain another string.

    if [[ ${testmystring} doesNotContain *"c0"* ]];then
        # testmystring does not contain c0
    fi

How can I do that, i.e. what is doesNotContain supposed to be?

[[ $testmystring != *c0* ]] && echo testmystring does not contain c0 — Jahid
– Jahid, Commented May 31, 2015 at 14:06
It's a inversed duplicate: read this answer and use else or not like in: if ! stringContain "c0" "$myteststring" ;then .... — F. Hauri - Give Up GitHub
– F. Hauri - Give Up GitHub, Commented May 31, 2015 at 14:23

cychoi · Accepted Answer · 2015-05-31 12:39:42Z

188

Use !=.

if [[ ${testmystring} != *"c0"* ]];then
    # testmystring does not contain c0
fi

See help [[ for more information.

answered May 31, 2015 at 12:39

cychoi

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13 Comments

cdarke Over a year ago

The { } and the quotes around c0 are superfluous.

cychoi Over a year ago

I agree they're superfluous for the mere example shown above. But if the variable name and the pattern string are getting more complex (e.g.: containing space in the pattern string), quoting them is necessary. Anyway, quoting them usually does no harm. :)

cdarke Over a year ago

True it does no harm, and if you enjoy typing them then knock yourself out! Sorry, I know this is pedantic, its just that I find people often use things like { } by rote without understanding when they are needed and when they are not (I did upvote you).

Paulo Neves Over a year ago

@cdarke: as far as i know not using {} incurs in a performance penalty because the shell cannot immediately assume it is a variable while with it, it can. I am not completely absolutely sure and worse i cant remember where I saw the numbers.

cdarke Over a year ago

@Randyman99: while I agree with your aim, I don't believe that adding superfluous characters when you don't understand what they do develops good programming practice. That's my point - too many people use them because of a cargo culture and they never learn what they are actually for - that's not good programming practice. Defensive programming is good, mindless programming is not good. Take that from someone who has been programming professionally for fifty years.

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Thiago Conrado · Accepted Answer · 2020-02-08 22:29:37Z

26

Bash allow u to use =~ to test if the substring is contained. Ergo, the use of negate will allow to test the opposite.

fullstring="123asdf123"
substringA=asdf
substringB=gdsaf
# test for contains asdf, gdsaf and for NOT CONTAINS gdsaf 
[[ $fullstring =~ $substring ]] && echo "found substring $substring in $fullstring"
[[ $fullstring =~ $substringB ]] && echo "found substring $substringB in $fullstring" || echo "failed to find"
[[ ! $fullstring =~ $substringB ]] && echo "did not find substring $substringB in $fullstring"

answered Feb 8, 2020 at 22:29

Thiago Conrado

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1 Comment

Tms91 Over a year ago

I think [[ ! $fullstring =~ $substringB ]] is the most fitting answer to this question. thanks

JJC · Accepted Answer · 2017-09-21 14:04:27Z

8

As mainframer said, you can use grep, but i would use exit status for testing, try this:

#!/bin/bash
# Test if anotherstring is contained in teststring
teststring="put you string here"
anotherstring="string"

echo ${teststring} | grep --quiet "${anotherstring}"
# Exit status 0 means anotherstring was found
# Exit status 1 means anotherstring was not found

if [ $? = 1 ]
then
  echo "$anotherstring was not found"
fi

edited Sep 21, 2017 at 14:04

JJC

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answered May 31, 2015 at 14:04

Roberto De Oliveira

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2 Comments

Jahid Over a year ago

You are using a cannon to kill a mosquito

JJC Over a year ago

Jahid is probably right, but, if someone is bent on this approach, this oneliner is more compact: if echo $teststring | grep -q $anotherstring ; then echo "found"; else echo "not found"; fi

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