A sequence of characters that have certain patterns of text (with meta-characters) that are searched for in a larger text file are called regular expressions:
$ ll /proc | grep cpuinfoIn the preceding command, thegreputility will search for thecpuinfotext in all lines of input text and will print lines that have thecpuinfotext.
Utilities such asgrep,sed, and awkuse regular expressions for filtering text and then apply various processing commands as required by the user. The lines that do not match the pattern will be rejected. The following diagram explains the same concept:
