Sed

Sed
	Chapter 2. Working in the Console

sed is a stream editor. This sounds scary in the WYSIWYG GUI world see https://devmanual.gentoo.org/tools-reference/sed/index.html or http://www.grymoire.com/Unix/Sed.html. There are reasons why bother with something that looks rather nostalgic and has not even mouse support and a menu bar:

sed takes all of its inputs from stdin a pipe can be used to feed it. So if called it freezes in the console. Therefore call it best with a file so an EOF comes.
sed can be called from scripts

sed is called as:

sed <options> '<command>' <inputfile>

The single quotes are not necessary but strongly recommended so that the shell never tries to expand it.

sed works as follows:

It takes the input file and the commands from stdin
It reads a line and stores it into its internal pattern buffer
It executes the command to the internal pattern buffer
It puts the result inside the internal pattern buffer to stdout (Note: The input file will not be modified except the -i option is added).
It goes to step 2 until the end of the file has been reached

Of course there are options to limit the commands just to certain lines.

A single line:

sed <options> '<linenumber><command>' <inputfile>

A range of lines:

sed <options> '<first line>,<last line><command>' < inputfile>

A regular expression:

sed '<regular expression><command>' <inputfile>

All lines from a first regular expression to a second regular expression.

sed '<first regular expression>,<second regular expression><command>' < inputfile>

d delete

p print

s/<find>/<replace>/g find a string and replace it globally

sed 's/\t/ /g' <inputfile> > <output file> replaces tab characters with a blank

sed -i 's/<xxx>/<yyyy>/g' <file> replaces xxx with yyyy in a file

-n usually all lines if not deleted will be printed. -n does just print the lines that match the -p command.


Commands		Regular expressions