gnu-grep

GNU grep

Learnings from GNU GREP and RIPGREP by Sundeep Agarwal'

Ensure that the version of grep you're using is 3.7 and above (the default that comes with MacOS is 2.6):

grep --version

grep (GNU grep) 3.8
Packaged by Homebrew
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Mike Haertel and others; see
<https://git.sv.gnu.org/cgit/grep.git/tree/AUTHORS>.

You can install this (as well as others using Homebrew)

Exercises

• Chapter 2

Simple commands

Example file: programming_quotes.txt

Criteria	grep Command	Manual Reference
Find a word from a text file	grep '[keyword]' [file]	Link
Regex pattern matching	grep -F '[regex_pattern]' [file]	Link
Case-insensitive searching	grep -i '[keyword]' [file]	Link
Inverse matching (ignore lines)	grep -v '[keyword]' [file]	Link
Line number	grep -n '[keyword]' [file]	Link
Line count	grep -c '[keyword]' [file]	Link
Limit output lines	grep -m[lines] '[keyword]' [file]	Link
Search multiple strings	grep -e '[first_keyword]' -e '[second_keyword]' [file]	Link
Search multiple strings (keywords from a file)	grep -f [keyword_file] [file]	Link
List files matching the pattern	grep -l '[keyword]' [file1] [file2]	Link
List files NOT matching the pattern	grep -L '[keyword]' [file1] [file2]	Link
Suppress filename output (default for single file)	grep -h '[keyword]' [file1] [file2]	Link
Show filename output (default for multiple files)	grep -H '[keyword]' [file]	Link
Match whole word only	grep -w '[keyword]' [file]	Link
Output exact match	grep -x '[keyword]' [file]	Link
Common lines between two files	grep -Fxf [file1] [file2]
Extract only matching pattern	grep -o '[keyword]' [file]	Link

Basic Regular Expression (BRE) / Extended Regular Expression (ERE) Regular Expressions

Example files: word_anchors.txt and words.txt

Typical commands:

Options	Description	Manual Reference
-G	can be used to specify explicitly that BRE is needed	Link
-E	will enable Extended Regular Expression (ERE). In GNU grep, BRE and ERE only differ in how metacharacters are specified, no difference in features	Link
-F	will cause the search patterns to be treated literally	Link
-P	will enable Perl Compatible Regular Expression (PCRE) (if available)	Link

Line Anchors

• ^ — start of line
• $ — end of line