Sed

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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