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Chapter 3. Working in the Console |  |
| Sed | ||
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Chapter 3. 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
A good introduction is http://www.grymoire.com/Unix/Sed.html
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
sed -i 's/<xxx>//g' <file> deletes xxx in a file
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| Commands |
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Regular expressions |
