How to use regexp in bash script

Question

# Checking if we dealing with 1050 or 1050 Ti
function gpu_check() {
  test="GPU 0: GeForce GTX 1050 (UUID: GPU-97acce0b-4304-01e9-ef9d-bc3230cae912)"
  echo "testing $test"
  if [[ $test =~ "\sGTX\s1050\s" ]]; then
    echo "foud 1050"
  else
    echo "no 1050's here"
  fi
}

i'm trying to use regex but all possible variants i can imagine, like double \, adding * and .*, using "$test" and many more, giving me not what i'm expecting.

testing GPU 0: GeForce GTX 1050 (UUID: GPU-97acce0b-4304-01e9-ef9d-bc3230cae912)

no 1050's here

How do i make it work?

\s is a PCRE-ism. It's not available in BRE or ERE regex syntaxes. — Charles Duffy
– Charles Duffy, Commented Jul 23, 2017 at 18:55
@medik, wrong -- bash does have regex syntax. And please, please don't ever advise folks to use the ABS as a reference -- it's the W3Schools of shell scripting, full of bad-practice examples and outdated content. — Charles Duffy
– Charles Duffy, Commented Jul 23, 2017 at 18:58

Community · Accepted Answer · 2020-06-20 09:12:55Z

3

re='[[:space:]]GTX[[:space:]]1050[[:space:]]'
[[ $test =~ $re ]]

...will do the trick.

\s is PCRE syntax. =~ only guarantees POSIX ERE syntax, so PCRE extensions aren't available. [[:space:]] is the POSIX-compliant equivalent.
You can't quote the regex without making it literal. That is to say -- it must be =~ $re and not =~ "$re" if you want the value in re to be treated as a regular expression rather than an exact string to search for.

Quoting from the documentation on the bash-hackers wiki:

Using the operator =~, the left hand side operand is matched against the extended regular expression (ERE) on the right hand side.

This is consistent with matching against patterns: Every quoted part of the regular expression is taken literally, even if it contains regular expression special characters.

Best practice is to put the regular expression to match against into a variable. This is to avoid shell parsing errors on otherwise valid regular expressions.

edited Jun 20, 2020 at 9:12

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answered Jul 23, 2017 at 18:56

Charles Duffy

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1 Comment

kusayu Over a year ago

Edit the typo please and i'll accept your answer. re=' bla "

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