sed Patterns
sed patterns I’ve actually used. Every entry has a date and context.
2026-03-07: Pipe Delimiter for Paths
Problem: Escaping hell with slashes in XML path substitution
Context: WLC VM migration, updating qemu paths in libvirt XML
The Fix:
# WRONG: escaping nightmare
sed -i 's/\/usr\/bin\/qemu-system-x86_64/\/usr\/libexec\/qemu-kvm/' file.xml
# RIGHT: use pipe delimiter
sed -i 's|/usr/bin/qemu-system-x86_64|/usr/libexec/qemu-kvm|' file.xmlRule: When substituting paths, use | or # as delimiter instead of /
Worklog: WRKLOG-2026-03-07
2026-03-XX: In-Place Editing with Backup
Problem: Edit file in-place but keep a backup
Context: Config file modifications
The Fix:
# Create backup with .bak extension
sed -i.bak 's/old/new/g' file
# GNU sed: no backup (dangerous!)
sed -i 's/old/new/g' file
# BSD/macOS sed: backup required or use empty string
sed -i '' 's/old/new/g' file # no backup on macOSRule: Always use -i.bak on production systems. Verify before deleting backup.
Worklog: Various
2026-03-XX: Delete Lines Matching Pattern
Problem: Remove all comment lines from config
Context: Cleaning up config files for comparison
The Fix:
# Delete lines starting with #
sed '/^#/d' file
# Delete empty lines
sed '/^$/d' file
# Delete both comments and empty lines
sed '/^#/d; /^$/d' file
# Delete lines containing pattern
sed '/pattern/d' fileWorklog: Various
2026-03-XX: Print Specific Line Range
Problem: Extract lines 100-110 from a file
Context: Examining specific section of log
The Fix:
# Print lines 100-110
sed -n '100,110p' file
# Print from line 100 to end
sed -n '100,$p' file
# Print line 100 and next 10 lines
sed -n '100,+10p' fileNote: For line ranges, prefer awk 'NR>=100 && NR⇐110' for practice.
Worklog: Various