Regex for "or" of multiple words in grep

All we need is an easy explanation of the problem, so here it is.

[Computer]$ grep "foo|bar" filename

I understand the above command should return each line in filename where there exits “foo” or “bar”. The man pages confirms | as the Regex or symbol and the code works for “foo” and “bar” independently. What am I missing?

How to solve :

I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.

Method 1

grep uses basic regular expressions (BRE) by default. From the man page:

Basic vs Extended Regular Expressions:
In basic regular expressions the meta-characters ?, +, {, |, (, and ) lose their special meaning; instead use the backslashed versions
\?, +, {, \|, (, and ).

So you either have to escape the |:

grep "foo\|bar" filename 

or turn on extended regular expressions:

grep -E "foo|bar" filename

Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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