bash
grep -RInw 'error' ./logsNotes
`-R` recurses, `-I` skips binary, `-n` prints line numbers, and `-w` uses word boundaries.
Regex for PCRE, grep, ripgrep, and sed
Regex patterns and command-line workflows for grep, ripgrep, sed, awk, and advanced PCRE-style features.
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grep, egrep, and ripgrep
Common command-line regex search patterns.
bash
rg -n -i 'timeout|timed out' .Notes
ripgrep is fast and respects ignore files by default.
ripgrep with PCRE2
Use lookbehind or advanced features through PCRE2 mode.
bashANYripgreppcre2lookbehind
bash
rg -n -P '(?<=ERROR: ).+' app.logNotes
`-P` enables PCRE2 for advanced constructs.
bash
grep -RInv '^\s*(#|$)' ./configNotes
Useful for skipping comments and blank lines.
bash
grep -E 'warn|error|fatal' app.logNotes
`grep -E` enables extended regular expressions.
bash
sed -E 's/[[:space:]]+/ /g' file.txtNotes
Great for one-line normalization tasks.
bash
awk '/^[0-9]{4}-[0-9]{2}-[0-9]{2}/ { print }' file.txtNotes
awk uses regex in pattern positions for line filtering.
PCRE and Advanced Features
Features common in PCRE-style engines and tools.
regex
(?>[A-Z][a-z]+)\s+\d+Notes
Useful when a branch should not be reconsidered.
regex
^(?<pair>\((?:[^()]++|(?&pair))*\))$Notes
Advanced PCRE technique for nested structures.
regex
^\((?:[^()]++|(?R))*\)$Notes
Powerful but niche; useful in engines that support recursion.
regex
^(?:(<))?\w+(?(1)>)$Notes
Useful for optional paired delimiters in PCRE-like engines.
regex
\b(?:https?://\S+)(*SKIP)(*F)|\bTODO\bNotes
Useful when excluding regions before matching the final target.
sed and Stream Editing
Regex-driven substitution and extraction with sed.
bash
sed -E 's/^([0-9]{4})-([0-9]{2})-([0-9]{2})$/\2\/\3\/\1/'Notes
Uses capture groups and backreferences in the replacement.
bash
sed -E 's/[[:space:]]+$//' file.txtNotes
Useful before committing source files.
bash
sed -E '/^$/! s/^/# /' notes.txtNotes
Combines a regex address with substitution.
bash
sed -En 's/.*"([^"]+)".*/\1/p' file.txtNotes
The `-n` flag suppresses normal printing; `p` prints only successful substitutions.
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