Regex for Log Parsing — Extract Fields from Log Lines
Quick Answer: Common log format regex: ^(\S+) (\S+) (\S+) \[([^]]+)\] "([^"]*)" (\d{3}) (\d+|-). Named capture groups make extraction clearer: (?P<ip>\S+) (?P<ident>\S+) (?P<user>\S+). Test your pattern against sample log lines to ensure all fields capture correctly.
FAQ
How do I parse Apache/Nginx access logs with regex?
Apache Combined Log Format: ^(\S+) \S+ \S+ \[([^]]+)\] "(\S+) (\S+) \S+" (\d{3}) (\d+) "([^"]*)" "([^"]*)"$. This captures IP, date, method, path, status, size, referer, user-agent.
Should I use regex or a log parser?
For standard formats (Apache, Nginx, syslog), use purpose-built parsers. Regex is best for custom log formats where no parser exists.