topic Re: awk behaviour in Operating System - HP-UX

awk behaviour

Wouter Jagers — Fri, 03 Jul 2009 12:42:13 GMT

Hi all,

Long time no see ;-)
I'm encountering some puzzling awk behaviour.

This is my (example) source file:

---
/home/jagersw > cat tst
021F 021F
0400 0400
04E2 04E2
012A 012A
---

I'd like to ask awk to find me the 2nd field for any given 1st one, using a variable.

However, what seems to work most of the time gives me grief at some occasions.

---
/home/jagersw > R1CHK="021F"

/home/jagersw > awk -v r1chk="$R1CHK" '$1==r1chk{print $2}' tst
021F

/home/jagersw > R1CHK="012A"

/home/jagersw > awk -v r1chk="$R1CHK" '$1==r1chk{print $2}' tst
012A
---

That's obviously what I want. Very nice.

However, with some values it doesn't seem to work:

---
/home/jagersw > R1CHK="04E2"

/home/jagersw > awk -v r1chk="$R1CHK" '$1==r1chk{print $2}' tst
0400
04E2

/home/jagersw > R1CHK="0400"

/home/jagersw > awk -v r1chk="$R1CHK" '$1==r1chk{print $2}' tst
0400
04E2
---

I'm puzzled. Maybe I just didn't get enough sleep last night, but I can't think of an explanation for this.

Anyone up for enlightening me ?

Thanks in advance !

Cheers,
Wout

Re: awk behaviour

Wouter Jagers — Fri, 03 Jul 2009 12:43:22 GMT

11.31 on ia64

Re: awk behaviour

James R. Ferguson — Fri, 03 Jul 2009 12:52:01 GMT

Hi Wout:

You are close:

# awk -v PAT="0400" '$1~PAT {print $2}' file

Regards!

...JRF...

Re: awk behaviour

James R. Ferguson — Fri, 03 Jul 2009 12:55:43 GMT

Hi (again) Wout:

I meant to add that the tilde allows the righthand side to be a constant (a sequence of characters between slashes) or an expression which can be evaulated. Here, we the evaulation to occur.

Regards!

...JRF...

Re: awk behaviour

Wouter Jagers — Fri, 03 Jul 2009 12:59:20 GMT

Thanks James !!

# awk -v PAT="0400" '$1~PAT {print $2}' file

Naturally I've tried a bunch of things (even ~/^PAT/), except this.

Works excellent now.

Any idea why I got this output ? Or should we just classify it under 'unexpected behaviour' :-)

Thanks again !

Cheers
Wout

Re: awk behaviour

James R. Ferguson — Fri, 03 Jul 2009 13:03:33 GMT

Hi (again) Wout:

> Any idea why I got this output ? Or should we just classify it under 'unexpected behaviour' :-)

Yes, read my second post. Using ~/^PAT/ means to match a constant, not evaulate. Notice how we dropped the '/'.

Regards!

...JRF...

Re: awk behaviour

Wouter Jagers — Fri, 03 Jul 2009 13:07:42 GMT

Indeed, that got cross-posted.
Thanks a bunch !

Cheers,
Wout

Re: awk behaviour

Dennis Handly — Sat, 04 Jul 2009 05:47:41 GMT

>with some values it doesn't seem to work: R1CHK="04E2"
>0400 04E2

My first thought was that you are mixing chars vs numbers. You shouldn't need no stinkin' ~ to be able to get a string exact match.

Looking closely at your output, 0400 and 04E2 ARE equal numerically!

So you need to convert to strings:
'$1 == r1chk "" {print $2}'
Or:
'BEGIN { r1chk = r1chk "" }
$1 == r1chk {print $2}'

>Anyone up for enlightening me?

It looks like nobody did.
Perhaps this is why you should use grep then awk. :-)

Re: awk behaviour

Wouter Jagers — Sat, 04 Jul 2009 18:31:24 GMT

Nice, concatenating a quote or zero for conversion was new to me, thanks for pointing this out !

How exactly are these the same, numerically ? I don't seem to experience the same issue with values like 04E4 or 012E ..?

Thanks for the continued enlightenment ;-)

Re: awk behaviour

Dennis Handly — Sun, 05 Jul 2009 02:13:32 GMT

>concatenating a quote or zero for conversion

I've seen awk scripts where they do "x + 0" to do the opposite.

>How exactly are these the same, numerically?

Scientific notation: 04E2 is 4 * 10**2 == 400

Re: awk behaviour

Wouter Jagers — Sun, 05 Jul 2009 06:46:49 GMT

Of course :-)
Thanks again !