Zero a column in a csv file with awk while skipping the header

Question

I would like to zero one column of a csv file. Let's assume the csv file looks like this:

col1|col2|col3
v   |  54| t
a   |  25| f
d   |  53| f
s   |  04| t

Using awk this way, gives me almost what I want

command:

awk -F'|' -v OFS='|'  '$2=0.0;7' input.csv > output.csv

the result

col1|0|col3
v   |0| t
a   |0| f
d   |0| f
s   |0| t

But notice that the column header has been also zeroed which is something I am trying to avoid. So I tried to skip the first line with the awk command but I am getting an empty file

awk -F'|' -v OFS='|'  'NR<1 {exit} {$5=0.0;7}' input.csv > output.csv

What am I missing?

@Ismael check the comment of user112638726 in the accepted answer. — Mohamed Ali JAMAOUI
– Mohamed Ali JAMAOUI, Commented Jul 9, 2015 at 9:47

fedorqui · Accepted Answer · 2015-07-09 09:26:45Z

6

Just apply the rule from the 2nd line on with a NR>1 {}:

$ awk -F'|' -v OFS='|'  'NR>1{$2=0.0}7' file
col1|col2|col3
v   |0| t
a   |0| f
d   |0| f
s   |0| t

Why wasn't your approach awk -F'|' -v OFS='|' 'NR<1 {exit} {$5=0.0;7}'working?

The expression NR<1{exit} is never True because NR is always at least 1.

This means that the second expression {$5=0.0;7} is always evaluated. The $5=0.0 is fine, but 7 is not printing as you would want to, because to print a line you need some kind of print instruction. It would work if you moved the 7 outside the braces, so that it will evaluate to True and the record will be printed: awk -F'|' -v OFS='|' 'NR<1 {exit} {$5=0.0}7'.

But this wouldn't do what you want. Instead, you may want to say NR==1 {next} to skip the first line. However, this will prevent it from being printed:

$ awk -F'|' -v OFS='|'  'NR==1{next} $2=0.0;7' file
v   |0| t
a   |0| f
d   |0| f
s   |0| t

edited Jul 9, 2015 at 9:26

answered Jul 8, 2015 at 9:54

fedorqui

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3 Comments

Mohamed Ali JAMAOUI Over a year ago

This is the right answer to resolve my issue, thanks. I will accept it when I can.

123 Over a year ago

@MedAli You also seem to not quite understand what 7 does in this context. As it is non zero it is seen as awk as true. The same goes for $2=0.0 but it is seen as false. So technically your first command(in the question) is seen as '$2=0.0{print $0};7{print $0}' or 'false{print $0};true{print $0}.

Mohamed Ali JAMAOUI Over a year ago

@User112638726, thank you. Now I do understand what 7 stands for :)

cxw · Accepted Answer · 2015-07-08 09:53:44Z

2

Change exit to next to skip the remaining actions for that first line.

answered Jul 8, 2015 at 9:53

cxw

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1 Comment

Mohamed Ali JAMAOUI Over a year ago

I did that, but the resulting file is empty

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