Text Processing (Grep/Sed/Awk)

Quit fighting regex for multi-line log blocks

🧩 The Challenge

Dealing with Java stack traces or multi-line app errors is a nightmare because standard grep only sees one line at a time. I’ve spent way too long trying to stitch fragmented log lines back together with custom scripts.

💡 The Fix

Use AWK’s record separator variable to define the start of your block instead of relying on line-by-line processing. It turns those messy, multi-line error blobs into single records you can actually search through.

awk -v RS='^Exception' '/my-target-error/ {print $0}' /var/log/app.log

⚙️ Why It Works

Setting RS tells AWK that a record begins whenever it hits that specific string, rather than at the default newline character. Everything between those markers gets treated as one chunk, making it trivial to grep for specific patterns across multiple lines.

🚀 Pro-Tip: Use the -v flag to pass shell variables into your awk script if you’re pulling search terms from a config file.

Linux Tips & Tricks | © ngelinux.com | 11/4/2026