Case insensitive regex in bash

By default regexes in [[ ]] are case sensitive. If you want to match in a case insensitive way you have to set the shell option nocasematch.

mytext="eXistenZ"
if [[ $mytext =~ existenz ]];
then 
 echo "yep"
else
 echo "nope"
fi

If you run the above script you should get "nope" as the output. For case insensitive matching just insert this into the script prior to the regex:

shopt -s nocasematch;

You can unset the nocasematch shell option using the following: shopt -u nocasematch

Here's a more complete example:

mytext="eXistenZ"
function testText
{
 if [[ $mytext =~ existenz ]];
 then 
  echo "yep"
 else
  echo "nope"
 fi;
}
testText
shopt -s nocasematch
testText

If you run that script then the output is:

nope
yep