sed - stream editor

A simple tool for editing streams… but what does that mean?

Remember that piping is flowing text from one program to another. Sometimes, we want to edit these streams!

It is a mini-language that allows use to quickly edit streams.

The use, 99% of the time

Find and replace. This is the same syntax you would use in Vi, so, it should be easy to remember.

s/this/that/g

• s substitute one thing for a something else
• this the word to find
• that the word to replace the found word with
• g globally… all of them!

See it in action

Generally we’d be processing a whole file, buy echo can give us a good example of how it works.

echo "one two three four" | sed s/three/tree/g 

But I need to replace 2 things

Pipe it through 2 sed commands!

echo "one two three four" | sed s/three/tree/g | sed s/four/fiddy/g

Other stuff it can do

Lots and lots. This is not a “sed in 30 minutes” primer.

The s in the above example is for ‘substitution’, which is pretty clear of what it does.

Other commands for sed…

• y - “Transliterate”… which is just “find and replace, but on single characters. echo aabbccd | sed y/abc/123/. You could do a substitution cypher very easily!
• d - Delete stuff. echo this\\nthat\\nother | sed /that/d
• And much more. See man sed or gnu’s documentation for more information.

Finally

It can look through text, to find text… then do something with that text.