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Fun tip #3: Split a line using ed

Written by Solène, on 04 December 2018.
Tags: #fun-tip #unix #openbsd

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In this new article I will explain how to programmaticaly a line (with a newline) using ed.

We will use commands sent to ed in its stdin to do so. The logic is to locate the part where to add the newline and if a character need to be replaced.

this is a file
with a too much line in it that should be split
but not this one.

In order to do so, we will format using printf(1) the command list using a small trick to insert the newline. The command list is the following:

/too much line
s/that /that

This search the first line matching “too much line” and then replaced "that " by "that0, the trick is to escape using a backslash so the substitution command can accept the newline, and at the end we print the file (replace ,n by w to write it).

The resulting command line is:

$ printf '/too much line0/that /that\0n0 | ed file.txt
> with a too much line in it that should be split
> should be split
> 1     this is a file
2       with a too much line in it that
3       should be split
4       but not this one.
> ?