SED

Stream EDitor tricks

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• Replacing lines
  • Example of disabling root login with passwords via SSH
• (Un)comment lines
  • Commenting
  • Uncommenting

Replacing lines

Used for changing configuration options that exist on a single line

Example of disabling root login with passwords via SSH

sed -i "s/.*PermitRootLogin.*/PermitRootLogin prohibit-password/g" /etc/ssh/sshd_config
sed -i "s/.*PasswordAuthentication.*/PasswordAuthentication no/g" /etc/ssh/sshd_config

The -i option means in-line editing of the specified file (/etc/ssh/sshd_config) The s at the start of the line is a regexp search+replace s/<regexp>/<replacement>/

(Un)comment lines

Commenting

sed -i "/needle/s/^/#/g" /path/to/haystack

Uncommenting

sed -i "/^#needle/s/^#*//g" /path/to/haystack