Sed

Sed is a stream editor, used to transforms text in an input stream a file or pipe. It operates by reading input line by line, applying editing commands, and outputting the modified lines.

Useful flags

• -n, --quiet: suppress automatic printing of pattern space
• -e, --expression: add the script to the commands to be executed
• -f, --file: add the contents of script-file to the commands to be executed
• -i, --in-place .bak: edit files in place (makes backup if SUFFIX supplied)

Example use cases

Find and replace all line containing word disabled to enforcing directly in file /etc/selinux/config

sed -i 's/disabled/enforcing/g' /etc/selinux/config

Delete line containing specific pattern

sed '/pattern/d' file.txt

Delete empty lines

sed '/^$/d' file.txt

Insert text before a specific line number:

sed '3i\This is a new line' file.txt

note: this going to insert new line before line 3

Parenthesize First Character of Each Word

echo "Hello World" | sed 's/\(\b[A-Z]\)/\(\1\)/g'

output:

(H)ello (W)orld

Best Practices

• Ensure to back up your files before apply changes with sed.
• Always test your SED command on sample file first to avoid misconfig.

Notes and improvement

• Adding more advanced sed command use case.
• Refactor markdown document.