Add string to columns in bash

Question

I have a comma-delimited file to which I want to append a string in specific columns. I am trying to do something like this, but couldn't do it until now.

re1,1,a1e,a2e,AGT
re2,2,a1w,a2w,AGT
re3,3,a1t,a2t,ACGTCA
re12,4,b1e,b2e,ACGTACT

And I want to append 'some_string' to columns 3 and 4:

re1,1,some_stringa1e,some_stringa2e,AGT
re2,2,some_stringa1w,some_stringa2w,AGT
re3,3,some_stringa1t,some_stringa2t,ACGTCA
re12,4,some_stringb1e,some_stringb2e,ACGTACT

I was trying something similar to the suggestion solution, but to no avail:

awk -v OFS=$'\,' '{ $3="some_string" $3; print}' $lookup_file

Also, I would like my string to be added to both columns. How would you do this with awk or bash?

Thanks a lot in advance

@ctac_ I added the awk tag now. My initial idea was not to go specifically for awk, but for either awk or bash. — Sos, Jun 12 '19 at 07:36

score 2 · Accepted Answer · answered Jun 11 '19 at 11:30

You can do that with (almost) what you have:

pax> echo 're1,1,a1e,a2e,AGT
re2,2,a1w,a2w,AGT
re3,3,a1t,a2t,ACGTCA
re12,4,b1e,b2e,ACGTACT' | awk 'BEGIN{FS=OFS=","}{$3 = "pre3:"$3; $4 = "pre4:"$4; print}'

re1,1,pre3:a1e,pre4:a2e,AGT
re2,2,pre3:a1w,pre4:a2w,AGT
re3,3,pre3:a1t,pre4:a2t,ACGTCA
re12,4,pre3:b1e,pre4:b2e,ACGTACT

The begin block sets the input and output field separators, the two assignments massage fields 3 and 4, and the print outputs the modified line.

Barmar · Answer 2 · 2019-06-11T11:35:03.183

1

You need to set FS to comma, not just OFS. There's a shortcut for setting FS, it's the -F option.

awk -F, -v OFS=',' '{ $3="some_string" $3; $4 = "some_string" $4; print}' "$lookup_file"

edited Jun 11 '19 at 11:35

answered Jun 11 '19 at 11:28

Barmar

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`IFS` is a *bash* thing, not an awk thing. In `awk`, the input field separator is just `FS`. That doesn't mean your solution is wrong, just that you're using the wrong terminology. – paxdiablo Jun 11 '19 at 11:34
@paxdiablo Thanks. Since I almost always use `-F`, I never have to deal with the actual variable name. – Barmar Jun 11 '19 at 11:35
Thanks a lot @paxdiablo and @Barmar. I'm wondering, what if the string to add has single quotations? I've tried with `"\'"` but it doesnt work – Sos Jun 11 '19 at 12:02
Nevermind, I found it in [here](https://stackoverflow.com/a/16491064/1379826) `awk -F"," -v quote="'" -v OFS="','" '{print quote $3,$4 quote}' $lookup_file` – Sos Jun 11 '19 at 12:10

score 1 · Answer 3 · answered Jun 11 '19 at 12:04

awk's default action is to concatenate, so you can simply place strings next to each other and they'll be treated as one. 1 means true, so with no {action} it will assume "print". You can use Bash's Brace Expansion to assign multiple variables after the script.

awk '{$3 = "three" $3; $4 = "four" $4} 1' {O,}FS=,

Add string to columns in bash

3 Answers3