egrep

View documentation for the original command

$ tldr grep

egrep [OPTION...] [PATTERN] [FILE...]

-i, --ignore-case
    Ignore case distinctions in PATTERN and input files

-v, --invert-match
    Select non-matching lines

-w, --word-regexp
    Select only matches that exactly match whole words

-x, --line-regexp
    Select only matches that exactly match entire lines

-c, --count
    Suppress normal output; print count of matching lines per file

-l, --files-with-matches
    Suppress normal output; print names of files with matches

-L, --files-without-match
    Suppress normal output; print names of files without matches

-n, --line-number
    Prefix each line of output with 1-based line number

-b, --byte-offset
    Prefix each line with 1-based byte offset

-H, --with-filename
    Always print filename before matching lines

-h, --no-filename
    Never print filename, even with multiple files

-r, -R, --recursive
    Recursively search directories

-e PATTERN, --regexp=PATTERN
    Use PATTERN as explicit search pattern

-f FILE, --file=FILE
    Read patterns from FILE

-A NUM, --after-context=NUM
    Print NUM lines of trailing context after each match

-B NUM, --before-context=NUM
    Print NUM lines of leading context before each match

-C NUM, -NUM
    Equivalent to --before-context=NUM and --after-context=NUM

-o, --only-matching
    Show only the part of a matching line that matches PATTERN

egrep (extended grep) is a powerful command-line tool for searching text files or input streams for lines matching a specified extended regular expression (ERE). Unlike basic grep, which uses basic regular expressions (BRE), egrep treats meta-characters like | (alternation), + (one or more), ? (zero or one), and parentheses () as grouping operators without requiring backslashes for escaping.

It processes one or more input files or standard input, printing matching lines to standard output by default. egrep is ideal for complex pattern matching in logs, code, configuration files, or data streams, supporting case-insensitive searches, counting matches, line numbering, and recursive directory traversal.

Key advantages include intuitive regex syntax for alternatives and repetitions, making it suitable for tasks like finding errors ('error|warn'), IP addresses ('([0-9]{1,3}\.){3}[0-9]{1,3}'), or multi-line patterns. Output can be customized with context lines, filenames, or offsets.

In modern Linux distributions, egrep is typically a symbolic link or alias to grep -E, providing identical functionality. It adheres to POSIX standards but extends with GNU-specific options for enhanced usability.

egrep is deprecated in modern GNU grep (since v2.5.3); use grep -E instead for extended regex. Not suitable for very large files without streaming; patterns are compiled once per invocation.

Supports | (or), + (1+), ? (0|1), * (0+), () (grouping), {n,m} (repetition) without escapes.

egrep 'error|warning' /var/log/syslog
egrep -r -i 'TODO|FIXME' /src/dir
egrep -c '^From:' mbox

Introduced in early Unix System V (1980s) as an extension to grep for ERE support. Standardized in POSIX.1-2001. In GNU coreutils, deprecated favoring unified grep with -E flag; remains for backward compatibility.

grep(1), fgrep(1), zgrep(1), sed(1), awk(1)