Fun tip #3: Split a line using ed

Author: Solène

Date: 04 December 2018

Tags: fun-tip unix openbsd

NIL.Dd December 04, 2018

.Dt "Splitting a line using ed"

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.

.Bd -literal -offset indent

this is a file

with a too much line in it that should be split

but not this one.

.Ed

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:

.Bd -literal -offset indent

/too much line

s/that /that\

,p

.Ed

This search the first line matching "too much line" and then replaced

"that " by "that\n", 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:

.Bd -literal -offset indent

$ printf '/too much line\ns/that /that\\\n\n,n\n' | ed file.txt

81

> 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.

> ?

.Ed