Sed

sed is a command to edit a text stream in batch mode.

For example,

sed "s/a/o/"

Will read your input (stream) from the keyboard and substitute every a by an o.

Usecases

• Remove leading white space

sed 's/^[ \t]*//'

• Replace strings

# echo "hello world" | sed "s/world/moon/"
hello moon

• Insert a line a beginning of file

sed -i '1i <This is now at the first line>' <filename>

• Replace several newlines by one

sed 's/\ \{1,\}/\ /g'

• change the protocol for a given port in /etc/services:

sed -ri "s/.{16}3200/sapdp00 3200/" /etc/services

Limitations

You cannot use sed to delete linebreaks, for this you must use tr.

See also

• Bash Skripting Tutorial
• piping
• grep
• regex