[SOLVED] awk print $0 vs print $1, $2, $3, etc.

vincix · 04-28-2017, 03:15 AM

I realised that there's a clear difference between print $0 and printing all the fields in a file in awk.

For instance, if I have a file with fields separated by commas and I want to change the FS to tabs (using OFS), if I do print $0, then awk will print the whole lines as they are regardless of the FS. It just outputs the lines from the file I feed it, instead of separating the fields with tabs.

So my question is, if I have a large file with let's say 20 fields, how can I make awk print all the fields while taking into account FS and OFS? In other words, is there another way the whole lines without using $1, $2, $3, etc. other than print $0?

syg00 · 04-28-2017, 03:28 AM

Just add "$1=$1" before your "print". Pick a field, any field ...

vincix · 04-28-2017, 03:38 AM

I don't understand. Where am I supposed to add it exactly? Before the print, within the brackets? I get syntax error. If I write print $1=$3, it only prints the 3rd field.

r3sistance · 04-28-2017, 04:15 AM

Quote:

Originally Posted by vincix

I don't understand. Where am I supposed to add it exactly? Before the print, within the brackets? I get syntax error. If I write print $1=$3, it only prints the 3rd field.

Seems you misread what you were advised.

Code:

$ echo "some random text here" | awk  'OFS="\t\t" {$1=$1; print $0}'
some            random          text            here
$ echo "some random text here" | awk  'OFS="\t\t" {print $0}'
some random text here

Anyways, there are better facilities for formatting such as the column facility, when it comes to formatting.

vincix · 04-28-2017, 05:19 AM

Right, thanks for clearing that up!
I've got another related question: what is the actual meaning of $1=$1? What is awk doing exactly by this expression?

r3sistance · 04-28-2017, 05:33 AM

It is writing the value of $1 to $1, essentially it is making no difference but as a parameter was updated, it also needs to update $0. It isn't a behavior I would personally rely on.

syg00 · 04-28-2017, 05:42 AM

I have relied on it for years. Never failed me yet.

grail · 04-28-2017, 07:51 AM

Just a btw, the print is not actually required, although to a beginner can make things clearer. So for your example of a csv you could do:

Code:

awk -F, '$1=$1' OFS='\t' file

vincix · 04-28-2017, 08:06 AM

Yes, that looks much cleaner. I'd prefer something more synthetic, of course. Thanks.