grep — Context & Recursive

Context Flags

Show 3 lines after each match

grep -A 3 'ERROR' /var/log/syslog

Show 2 lines before each match

grep -B 2 'FATAL' app.log

Show 5 lines of context (before and after)

grep -C 5 'Exception' app.log

Preserve color through pipe to pager

grep --color=always 'pattern' | less -R

Show function definition around match

grep -nP -B2 -A10 'def report_to_wazuh' mail-detector.py

Count matches per file (files with >5 xrefs)

grep -rcP --include='*.adoc' 'xref:' docs/modules/ROOT/pages/ | awk -F: '$2 > 5'

Extract only the matched portion

grep -oP '\d{1,3}(\.\d{1,3}){3}' /etc/hosts
# Output: 10.50.1.50
#         10.50.1.90
#         127.0.0.1

Extract with \K reset — captures only the value after the key

grep -oP 'port-\w+: '\''\K[^'\'']+' docs/antora.yml
# Output: 25
#         587
#         993

Recursive search through a directory tree

grep -r 'pattern' /etc/

Recursive with file glob filter and line numbers

grep -rn --include='*.py' 'import' .

Multiple include globs

grep -rnP --include='*.{yaml,yml}' 'password' /etc/

Recursive excluding specific directories

grep --exclude-dir={.git,node_modules,vendor} -rn 'TODO' .

Files-only mode — list files containing pattern

grep -rlP --include='*.adoc' ':toc:' docs/
# STD-004 violation: Antora provides sidebar TOC globally

Invert files — list files NOT containing pattern

grep -rLP --include='*.adoc' ':description:' docs/modules/ROOT/pages/
# Missing :description: header — find non-compliant pages