how to construct regex to compare case insensitive strings in shell script?

Question

I am passing command line arguments to a shell script and it is being compared aganist a regular expression. The following code is case-sensitive:

[[ $1 =~ ^(cat)|(dog)$ ]] && echo "match" || echo "no match"

How can I modify this regex that will ignore cases? I would be able to pass cAt and it should match.

I want to use /i regex flag as it ignores cases. But how do I use it inside a shell script? I have tried [[ $1 =~ /(cat)|(dog)/i ]] but the script exited with a syntax error.

StackOverflow has a similar question but it does not answer my inquiry. I want to use test to compare both strings and not interested to use shopt -s nocasematch or grep <expression>

Derviş Kayımbaşıoğlu · Accepted Answer · 2018-12-23 00:19:11Z

3

just use

shopt -s nocasematch

before your command.

alternatively

shopt -s nocasematch && [[ 'doG' =~ (cat)|(dog) ]] && echo 'hi' || echo 'no match'

answered Dec 23, 2018 at 0:19

Derviş Kayımbaşıoğlu

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1 Comment

blackbeard Over a year ago

Asker said that he does not want to use shopt -s nocasematch :/

inetknght · Accepted Answer · 2024-08-15 01:45:20Z

0

While the accepted answer's shopt -s nocasematch is fine for many cases, I very much prefer to keep shopt -u nocasematch to be more explicit about matches.

This uses bash's variable expansion and asks bash to convert the expanded output to lowercase [documentation] to achieve your desired result, while also allowing other code to be case sensitive when needed:

shopt -u nocasematch # turn regex case-sensitivity on
test() { [[ "${1,,}" =~ ^(cat)|(dog)$ ]] && echo "match" || echo "no match"; }
test cat
test cAt
test ""

->

match
match
no match

answered Aug 15, 2024 at 1:45

inetknght

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