Print line numbers starting at zero using awk

Question

Can anyone tell me how to print line numbers including zero using awk?

Here is my input file stackfile2.txt

when I run the below awk command I get actual_output.txt

awk '{print NR,$0}' stackfile2.txt | tr " ", "," > actual_output.txt

whereas my expected output is file.txt

How do I print the line numbers starting with zero (0)?

@user790049, don't make us chase links to find out what the problem is. Show a small sample input and tell us what you want the output to look like. http://stackoverflow.com/help/how-to-ask — glenn jackman, Dec 23 '13 at 23:08
The links to the files are broken. Could you [edit] the question to include some proper [mcve]? — fedorqui, Nov 27 '15 at 13:10

score 121 · Accepted Answer · edited May 02 '14 at 17:21

121

NR starts at 1, so use

awk '{print NR-1 "," $0}'

edited May 02 '14 at 17:21

jaypal singh

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answered Dec 23 '13 at 22:25

Lance Roberts

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It might be nicer to set the output field separator to the comma: `awk -v OFS="," '{print NR-1, $0}' file`. – fedorqui Nov 27 '15 at 13:11
1

If you're looking for custom start value and other customizations, look at the answer based on `nl` below. – malana Feb 12 '19 at 14:52

BMW · Answer 2 · 2017-09-20T11:19:09.397

18

Using awk.

i starts at 0, i++ will increment the value of i, but return the original value that i held before being incremented.

awk '{print i++ "," $0}' file

edited Sep 20 '17 at 11:19

answered Dec 24 '13 at 05:24

BMW

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+ for one character shorter than `NR-1` You could also have used `awk '{print i++,$0}' OFS=, file` but this would be longer. – Jotne Dec 24 '13 at 08:45
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@Jotne When out for golfing, `awk '$0=i++","$0'` beats it ;-) – Adrian Frühwirth May 02 '14 at 17:57

Jon · Answer 3 · 2017-04-21T22:52:51.100

Another option besides awk is nl which allows for options -v for setting starting value and -n <lf,rf,rz> for left, right and right with leading zeros justified. You can also include -s for a field separator such as -s "," for comma separation between line numbers and your data.

In a Unix environment, this can be done as

cat <infile> | ...other stuff... | nl -v 0 -n rz

or simply

nl -v 0 -n rz <infile>

Example:

echo "Here 
are
some 
words" > words.txt

cat words.txt | nl -v 0 -n rz

Out:

000000      Here
000001      are
000002      some
000003      words

Chris Koknat · Answer 4 · 2017-09-26T18:04:08.917

2

If Perl is an option, you can try this:

perl -ne 'printf "%s,$_" , $.-1' file

$_ is the line
$. is the line number

edited Sep 26 '17 at 18:04

answered Oct 07 '15 at 00:09

Chris Koknat

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Print line numbers starting at zero using awk

4 Answers4

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