SHELL

grep search match

grep -rn regex_search folder_where_to_search
#Ex: search pattern in "." current folder (r) recursively
grep -rn pattern .

grep or match

$ grep "PATTERN1|PATTERN2" FILE
$ grep -E "PATTERN1|PATTERN2" FILE
$ grep -e PATTERN1 -e PATTERN2 FILE
$ egrep "PATTERN1|PATTERN2" FILE