...
grep and regular expressions
The grep command
- grep -P '<pattern>' searches for <pattern> in its input, and only outputs lines containing it
- always enclose '<pattern>' in single quotes to inhibit shell evaluation!
- pattern-matching metacharacters are very different from those in the shell
- -P says to use Perl patterns, which are much more powerful than standard grep patterns
- -v (inverse match) – only print lines with no match
- -n (line number) – prefix output with the line number of the match
- -i (case insensitive) – ignore case when matching
- -l says return only the names of files that do contain the pattern match
- -L says return only the names of files that do not contain the pattern match
- -c says just return a count of line matches
- -A <n> (After) and -B <n> (Before) – output '<n>' number of lines after or before a match
- always enclose '<pattern>' in single quotes to inhibit shell evaluation!
Regular expressions
A regular expression (regex) is a pattern of characters to search for and metacharacters that control and modify how matching is done.
...