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What is the most efficient case-insensitive grep usage?

Posted by: admin November 30, 2017 Leave a comment


My objective is to match email addresses that belong to the Yahoo! family of domains. In *nix systems (I will be using Ubuntu), what are the benefits and drawbacks to any one of these methods for matching the pattern?

And if there is another, more elegant solution that I haven’t been capable of imagining, please share.

Here they are:

  • Use grep with option -i:

grep -Ei "@(yahoo|(y|rocket)mail|geocities)\.com"

  • Translate characters to all upper case or lower case then grep:

tr [:upper:] [:lower:] < /path/to/file.txt | grep -E "@(yahoo|(y|rocket)mail|geocities)\.com"

  • Include a character set for each character in the pattern (the below would of course not match something like “@rOcketmail.com”, but you get the idea of what it would become if I checked each character for case):

grep -E "@([yY]ahoo|([yY]|[rR]ocket)[mM]ail|[gG]eo[cC]ities)\.[cC][oO][mM]" /path/to/file.txt


grep -i turned out to be significantly slower than translating to lowers before grepping, so I ended up using a variation of #2.

Thanks @mike-w for reminding me that a simple test goes a long way.