Grep

Search for text inside of files

Description

Grep is a really useful tool for quickly finding what you're looking for. If you know a file somewhere has some content, or just want to find all files with a certain pattern in them, Grep is the perfect tool for the job. It's written in C and highly optimized, meaning you can quickly search through lots of files.

$ grep [OPTIONS...] PATTERNS [FILES...]

• OPTIONS can be any flags to change the way the search works, or matches are displayed

• PATTERNS are a string containing one or more patterns to search for, separated by newline characters (\n). To put a newline character in an argument you can use the $'first\nsecond' syntax

• FILES are the files to search through for the PATTERNS. If not specified, it will read from standard input (piping into grep). If in recursive mode with -r, it will default to the current directory but can be any directory

Simple example

$ grep something file.txt
And here is something.

See all documentation about the options with man grep

Options

The are a few common and really useful options to know in Grep:

• -r: Recursively search a directory (default: current)

• -v: Invert search, matching lines where no match

• -i: Search case-insensitive (uppercase/lowercase doesn't matter)

• -n: Print the line number of the match in the file

• -o: Only output match (no text around)

• -a: Show all matches (also binary files)

• -b: Show byte-offset of matches

• -l: List files that match instead of showing the match

• Simple Regular Expressions (RegEx) are enabled by default in PATTERNS

  • -F: Treat PATTERNS as fixed strings, not regular expressions

  • -P: Use perl-compatible regular expressions (PCRE) including all advanced RegEx features

Some options are also available by using egrep (-E), fgrep (-F) and rgrep (-r) to quickly set the options without having to add the flag.

Examples

# # Select files and output
$ grep -r "something"  # Search recursively in current directory for "something"
$ grep -v "something" file.txt  # Find all lines in file that don't match "something"
$ grep "something" *.txt  # Search "something" in all .txt files (current directory only)
$ grep -r "something" --include "*.txt"  # Recursivly search "something" in .txt files
$ grep -ab "something" file.bin  # Show all (binary) matches and byte-offset
$ grep -r -l "something"  # List filenames that match "something" recursively
$ grep -B2 -A5 "something" file.txt  # Show 2 lines before, and 5 lines after match

# # Patterns
$ grep -r -i "something"  # Search case-insensitively for "something"
$ grep "CTF{.*}" file.txt  # Search for flag format in file
$ grep -P "\x73\x6f\x6d\x65\x74\x68\x69\x6e\x67" file.txt  # Search for hex bytes in file
$ xxd -p file.txt | grep "aabbccdd"  # Search for hex bytes using xxd
$ grep $'first\nsecond' file.txt  # Search for multiple patterns in one file

Tip: Also check out ripgrep for a Rust implementation of most grep features, with better defaults for recursive searching while skipping unnecessary files