Text Processing (Grep/Sed/Awk)

Stop mangling multi-line logs with simple grep

🧩 The Challenge

Dealing with Java stack traces or application logs that span twenty lines is a nightmare when you just want to see the error block. Grep is great until it only prints the single line containing the match, leaving you with zero context.

💡 The Fix

Use Perl-compatible regular expressions to pull entire log stanzas based on a single line match. It saves you from having to scroll back through thousands of lines to find where the error actually started.

grep -Pz '(?s)ERROR_STRING.*?(?=\n\n|\Z)' your_log_file.log

⚙️ Why It Works

The -P flag enables Perl regex and -z treats the entire file as a single line by replacing newlines with null characters. That (?s) flag makes the dot match newlines, allowing the regex to grab everything between your trigger and the next blank line.

🚀 Pro-Tip: If your log file is massive, use the –null-data flag cautiously because it reads the whole thing into memory.

Linux Tips & Tricks | © ngelinux.com | 10/31/2026