====== grep and ripgrep ======

===== Mode flags: what the pattern means =====

<code bash>
grep 'foo' f        # BRE: + ? ( ) | need backslashes
grep -E 'a|b' f     # ERE: modern syntax, no backslashes
grep -F 'a.b' f     # literal string: dots are dots
grep -P '\d+' f     # PCRE (Perl regex): \d \w lookahead etc.
rg 'pattern'        # Rust regex: PCRE-like minus backrefs/lookaround
</code>

See [[terminal:scripting:regex|regex]] for the flavor differences.

===== Search control =====

<code bash>
grep -i 'error'             # case-insensitive
grep -v 'debug'             # invert: non-matching lines
grep -w 'port'              # whole word only
grep -x 'exact line'        # whole line only
grep -q pat f && echo yes   # quiet: just the exit code
grep -c pat f               # count matching LINES (not matches)
</code>

===== Output shaping =====

<code bash>
grep -n pat f          # line numbers
grep -H pat *          # always show filename
grep -o 'pat[^ ]*' f   # print only the matched part
grep -m 5 pat f        # stop after 5 matches
grep -A3 -B2 -C1 pat   # after / before / context lines
grep --color=always    # keep colors when piping
</code>

===== Recursive =====

<code bash>
grep -r pat dir/                  # all files under dir
grep -rl pat dir/                 # filenames only: good for find-replace
grep -r --include='*.conf' pat /etc
grep -r --exclude-dir={.git,node_modules} pat .
</code>

''rg'' does all this by default and respects .gitignore:

<code bash>
rg pat                    # recursive, numbers, colors
rg -l pat                 # files only
rg --type py pat          # by file type; rg --type-list
rg -g '*.conf' pat        # glob filter
rg -tmd -g '*.md' pat     # markdown files only
rg --hidden pat           # include dotfiles (still skips .gitignore'd)
rg -uuu pat               # nothing ignored (careful)
</code>

===== Exit codes: scripting =====

<code bash>
if grep -q pat file; then ...      # 0 found, 1 not found, 2 error
grep -q pat file || handle_missing
</code>

''grep -c'' prints ''0'' AND exits 1: don't rely on the count alone.

===== Fixed strings & special chars =====

<code bash>
grep -F 'a[b]c' f              # literal brackets
grep -e '-pattern' f           # pattern starting with dash
grep -f patterns.txt f         # patterns from a file (OR'd)
</code>

===== Patterns that earn their keep =====

<code bash>
grep -vE '^\s*(#|$)' f                          # no comments/blanks
grep -oE '[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+'       # IPs
grep -E '^(ERROR|WARN)' log                     # tagged lines
grep -zoE 'start.*end' f                        # across newlines (GNU -z)
ls | grep -v '\.md$'                            # non-md files
</code>

===== Gotchas =====

  * ''grep 'a*''' matches everything (''a*'' means zero or more ''a''): for a literal asterisk use ''grep 'a\*''' or ''grep -F 'a*'''.
  * Binary files: ''grep'' says "Binary file matches": force text with ''-a'' or
  suppress with ''-I''.
  * ''zgrep''/''bzgrep''/''xzgrep'' for compressed files.
  * ''grep'' returns per LINE: for "files containing X that also lack Y":
  ''comm -23 <(grep -l X *) <(grep -l Y *)''.


===== See Also =====

  * [[terminal:scripting:start|Scripting Index]]
  * [[terminal:tools:start|CLI Tools]]
  * [[terminal:start|Return to terminal]]
  * [[start|Return to wiki home]]