How to add a line number follow by a tab to a text file

Question

I tried using

nl -ba -s '\t' full_media > full_media2

But it really did not add the tab, but it added actually the "\t" text after the line number. The file im editing is a CSV file and here by i'm trying to add a new column to the beginning with id.

Answer 1

If you're using a modern shell like bash or zsh, use $ so that the shell evaluates \t and replaces it with an actual tab:

nl -ba -s $'\t' full_media > full_media2

Even so, if you examine the output, it looks like the default separator is a tab:

$ nl -ba -s $'\t' ~/at.sh | od -c
0000000                       1  \t   n   o   h   u   p       s   g    
$ nl -ba  ~/at.sh | od -c        
0000000                       1  \t   n   o   h   u   p       s   g    

Indeed, the default separator is tab, as specified by POSIX. From man nl:

   -s  sep
          Specify  the  characters  used in separating the line number and
          the corresponding text line. The default sep shall be a <tab>.

---

To add a column to the CSV, try using Python:

#! /usr/bin/env python2

from sys import stdin, stdout
import csv

csvin = csv.reader(stdin, delimiter='\t')
csvout= csv.writer(stdout, delimiter='\t')
count = 1

for row in csvin:
    csvout.writerow ([count] + row)
    count = count + 1

Save it as a script (say nl.py) and run:

python2 nl.py < full_media > full_media2