Insert Line in File When Group of Lines Changes

Question

Let's say I have a text file like this:

group1 hello
group1 there
group1 nice line
group2 here
group2 we
group2 go

What I want to do is insert a line when the group of lines changes, something like:

group1 hello
group1 there
group1 nice line
---------------------------------------
group2 here
group2 we
group2 go

I don't care if that line also appears as the first and/or last line. At this time I only need something that separates the information.

How do I do that with sed or awk? Or maybe there are other ways?

chaos · Accepted Answer · 2016-01-27 07:12:43Z

1

With awk:

awk 'NR!=1&&x!=$1{print "---"} {x=$1}1' file

NR!=1&&x!=$1: applies for all lines, except the first line and checks if the first field has changed.
print "---": if yes, print the dashes.
{x=$1}: set x for the next iteration.
1: a true condition that awk prints each line.

answered Jan 27, 2016 at 7:12

chaos

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