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Regular expressions - example

Regular expressions are very handy to search for certain strings. Note that there are different versions of grep.

source: https://unix.stackexchange.com/questions/498925/grep-not-working-as-expected

GNU grep uses by default Basic Regular Expressions (BRE), but it also let you use Extended Regular Expressions (ERE) and Perl-compatible Regular Expressions (PCRE).

Please note that neither BRE nor ERE support \s nor \d, but they have similar feature

To be able to use for instance \t (tab character) you have to invoke grep -E as in

grep -P "^[ \t]*print" test.txt

This searches in file test.txt for

• start of line (^)
• followed by zero or more [space or tab]
• followed by the word ‘print’

Written on December 27, 2021