grep с регулярными выражениями, совместимыми с Perl (a grep with Perl-compatible regular expressions.)
Диагностика (Diagnostic)
Exit status is 0 if any matches were found, 1 if no matches were
found, and 2 for syntax errors, overlong lines, non-existent or
inaccessible files (even if matches were found in other files) or
too many matching errors. Using the -s option to suppress error
messages about inaccessible files does not affect the return
code.
