grep

Recursive case insensitive search; print the filename and the line:

_$: grep -nri "word" ./file

Recursive case insensitive search; print just the filename:

_$: grep -lri "word" ./file

Search when multiple matches per line are possible:

_$: grep -o "word" ./file

Search with basic regular expressions (BRE):

_$: grep -n "^wor*" ./file

Search with extended regular expressions (ERE):

_$: grep -nE "(word1|word2)" ./file

Search with Perl-compatible regular expressions (PCRE):

_$: grep -oE "GET /ru/.* HTTP/1.1\" 404" access.log.1 | grep -oP "/ru/.*? "

Ignoring a directory:

_$: grep -nri --exclude-dir='dir' "word" ./*

find + grep

Find all files older than a year with the word ** SPAM **:

_$: grep -l '** SPAM **' $(find . -mtime +365)

Find all files older than a year with the word ** SPAM ** and delete them:

_$: find . -mtime +365 -print0 | xargs -0 -I {} grep -l '** SPAM **' {} | xargs -I {} rm {}