grep -E (extended regex) is the right tool 95% of the time. Combine -i (case-insensitive), -v (invert), -n (line numbers), -B/-A (context lines).
Bash
# Lines matching either of two patterns
grep -E "(ERROR|FATAL)" /var/log/app.log
# Inverse: lines NOT matching
grep -v "DEBUG" /var/log/app.log
# Case-insensitive search with line numbers and 2 lines of context
grep -inB2 -A2 "stripe" /var/log/app.log
# Match a regex with groups (use -o to print only the match)
grep -oE 'user_id=[0-9]+' /var/log/app.log | sort -u
# Use ripgrep (rg) — faster and respects .gitignore by default
rg "ERROR" --type=log -C 2Save your own code snippets
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