[SOLVED] awk with if condition

indianovice · 07-11-2012, 07:54 AM

Hi,

I have a file which is like

A B C D
1 2 2 3
1 4 6 3
3 3 3 3

(The delimiter is tab)

Now I want to replace the 3rd column with space but I cant use anything like cat file.txt |awk '{$3=" "};1' because I want the 'C' to be still there. ie the output should be have a blank 3rd column with C as its heading(only the numbers should be removed)

Please help!

acid_kewpie · 07-11-2012, 08:21 AM

just use the if statement, as you said:

awk '{if (NR==1) {print} else { print $1 " " $2 " " $4 }}'

indianovice · 07-11-2012, 08:27 AM

Hi,

Thanks ! It worked. But I want the change to be reflected in the original file, and not just print the output. How can I do that?
Also,the output was like:

A B C D
1 2 3
1 4 3
3 3 3

Why is it so?

grail · 07-11-2012, 08:33 AM

Code:

awk 'NR>1{$3=" "}$1=$1' OFS="\t" file

jschiwal · 07-11-2012, 09:05 AM

You will need to redirect the output to a temporary file, and then replace the original file.

indianovice · 07-11-2012, 09:09 AM

awk 'NR>1{$3=" "}$1=$1' OFS="\t" aaa.txt
A B C D
1 2 3
1 4 3
3 3 3
cat aaa.txt
A B C D
1 2 2 3
1 4 6 3
3 3 3 3

But I want aaa.txt to be changed to
A B C D
1 2 3
1 4 3
3 3 3

David the H. · 07-11-2012, 12:12 PM

Please use ***[code][/code] tags*** around your code and data, to preserve formatting and to improve readability. Please do not use quote tags, bolding, colors, or other fancy formatting.

The majority of command line tools, including awk, only print to stdout and do not alter the input file. And you can't just redirect the output back into the same input file, as the redirection operator will overwrite it before it even gets read. For the most part you need to output to a temporary file or variable first, and then replace the original.

Code:

awk 'NR>1{$3=" "}$1=$1' OFS="\t" aaa.txt >tempfile
mv -f tempfile aaa.txt

indianovice · 07-12-2012, 01:32 AM

Thank you all for the answers!

Could you pls explain why $1=$1 is used?

grail · 07-12-2012, 03:40 AM

It could be any valid field number, 1 is just easy, and it will restructure the line with OFS between each field. Change it to 1 (one) and see the difference.