Question

I’m having trouble creating 2 commands that insert one word (different between the commands) at the beginning of every line with step = 2.

For example:

Before:
10
10
10
10

After:
group1 10
group2 10
group1 10
group2 10

So what I would want is that 1 command starts inserting the word ‘group1’ to every odd line, while the second command inserts the word ‘group2 to every even.

The number 10 is chosen randomly as a substitute for my data numbers

Hope you could help me with this.

Cheers,

Answer 1

You can do this with sed, here handling odd and even lines separately:

sed '1~2 s/^/group1 /' original.txt | sed '2~2 s/^/group2 /' >modified.txt

The 1~2 matches every second line starting with first, and 2~2 matches every second line starting from second. “s” substitutes, “^” matches the start of the line