Help with awk if/else-statement

Question

Help with awk if/else-statement

Hi all

I'm trying to write an awk script to process some text file based on the number of fields in each line. That is, if a line contains, for instance, 10 words, I'd like to process it differently than if it has 11 words. However, I don't seem able to get the if/else-statements correct.

This is the script:

#!/bin/awk
{
if ( NF = 10 )
print "10," NF "," $0
else
print "xx," NF "," $0
}

I'd expect that the script will output something like this:

10,10,line with 10 words
xx,13,line with 13 words

Instead I'm getting:

10,10,line with 10 words
10,10,line with 13 words

I changed the script to

{
if ( NF = 500 ) # of course, there are no lines with 500 fields!
print "500," NF "," $0
else
print "xx," NF "," $0
}

and now I'm getting this:

500,500,line with 10 words
500,500,line with 13 words.

It seems that instead of comparing "NF" to the number 10 (or 500), the script is SETTING the variable NF to 10 (or 500).
Why????

TIA, Tina

G5 Dual 1.8 (and lots of others, @ work and @ home), Mac OS X (10.5.6), iPhone 3G

Posted on Oct 23, 2009 3:22 AM

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Answer 1

Oct 23, 2009 3:48 AM in response to Tina Siegenthaler

Replying to my own post...

I replaced "if ( NF = 10 )"
by "if ( NF ~ 10 )"

and now it works, but is that correct or could this be a source for other problems later?

Tina

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Answer 2

Oct 23, 2009 6:58 AM in response to Tina Siegenthaler

Your instincts are right. Using one = means assignment. Use == for comparison.

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Answer 3

Oct 23, 2009 7:06 AM in response to Tina Siegenthaler

Thanks, now it works. Strange is, "==" is what I had tried first, but then it wouldn't work, so I guess something else was wrong - which I have now corrected without noticing...

Tina

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Answer 4

BobHarris

Level 9

56,933 points

Oct 23, 2009 7:10 AM in response to Tina Siegenthaler

In the future, please enclose your code snippits in


... your code here ...

This will protect your code from the forum stealing characters it things are formatting meta characters, and it will preserve your indentation.

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Answer 5

BobHarris

Level 9

56,933 points

Oct 23, 2009 7:20 AM in response to Tina Siegenthaler

The awk basic form is


selection { action }
selection { action }
....
selection { action }

where each line of the file is checked against each "selection" statement.

So you could have formed your awk as


#!/bin/awk
NF == 10 { print "10," NF "," $0; next }
NF == 11 { print "xx," NF "," $0; next }
{ print "everything else" }

Your way is NOT wrong, I'm just trying to point out alternate ways of using awk.

The same line may be processed by multiple "selection" statements which is why I included "next" in the { action } section.

You might find the following web page interesting awk reading.
<http://h30097.www3.hp.com/docs/base doc/DOCUMENTATION/V51BHTML/ARH9WBTE/WKXXXXXX.HTM>

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Answer 6

Oct 23, 2009 7:35 AM in response to BobHarris

BobHarris wrote:


... your code here ...

Sorry, forgot about that - the script was so simple... I won't forget it in the future, promise!

Tina

Message was edited by: Tina Siegenthaler

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Answer 7

Oct 23, 2009 7:36 AM in response to BobHarris

Thanks for the tip and the link, I'll check it out. The script is actually not finished yet, so I'll probably run into some other problems soon, so the link might come in handy...

Tina

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