How do I use regular expressions in bash scripts?

RegexBashConditional

Regex Problem Overview

I want to check if a variable has a valid year using a regular expression. Reading the bash manual I understand I could use the operator =~

Looking at the example below, I would expect to see "not OK" but I see "OK". What am I doing wrong?

i="test"
if [ $i=~"200[78]" ]
then
  echo "OK"
else
  echo "not OK"
fi

Regex Solutions

Solution 1 - Regex

It was changed between 3.1 and 3.2:

> This is a terse description of the new features added to bash-3.2 since the release of bash-3.1. > > Quoting the string argument to the [[ command's =~ operator now forces string matching, as with the other pattern-matching operators.

So use it without the quotes thus:

i="test"
if [[ $i =~ 200[78] ]] ; then
    echo "OK"
else
    echo "not OK"
fi

Solution 2 - Regex

You need spaces around the operator =~

i="test"
if [[ $i =~ "200[78]" ]];
then
echo "OK"
else
echo "not OK"
fi

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Content TypeOriginal AuthorOriginal Content on Stackoverflow
QuestionidrosidView Question on Stackoverflow
Solution 1 - RegexpaxdiabloView Answer on Stackoverflow
Solution 2 - RegexmichielView Answer on Stackoverflow