topic Re: awk and else statements in Operating System - Linux

awk and else statements

lawrenzo_1 — Fri, 18 May 2007 10:55:34 GMT

Hi all,

I have created an awk statement that works well:

for i in `etc etc`
do
|awk '/Virtual I\/O Bus/ {line=line+1};END{if(line>1) print serv": virtual server"}'
done

however how can I use else in this statement - the following does not work:

|awk -v serv=$i '/Virtual I\/O Bus/ {line=line+1};END{if(line>1) print serv": virtual server";else print serv": not a virtual server"}'

all servers in the list come back with

serv: not a virtual server

any help would be great

Thanks

Chris

Re: awk and else statements

James R. Ferguson — Fri, 18 May 2007 11:08:19 GMT

Hi Chris:

|awk -v serv=$i '/Virtual I\/O Bus/ {line=line+1};END{if(line>1) {print serv": virtual server"} else {print serv": not a virtual server"}}'

Regards!

...JRF...

Re: awk and else statements

A. Clay Stephenson — Fri, 18 May 2007 11:17:21 GMT

First, you don't need your line variable because awk has the built-in NR variable.

Now try this:
ls | awk 'END { if (NR > 1) {print "More"} else {print "Less than two"} }'

echo "One thing" | awk 'END { if (NR > 1) {print "More"} else {print "Less than two"} }'

I'm just using ls and echo to supply more than one line and one line respectively.

Re: awk and else statements

spex — Fri, 18 May 2007 11:20:27 GMT

Hi Chris,

Both cases of your if-else statement work properly--unaltered--on my system. Make sure you have specified the correct search pattern and look out for any unexpected input.

PCS

Re: awk and else statements

Sandman! — Fri, 18 May 2007 11:54:53 GMT

Either try parenthesizing the if else or Most likely it is the semi-colon before the END that maybe causing erroneous results so try removing it and see if that fixes it or convert it into a multi-line awk construct:

awk -v serv=$i '/Virtual I\/O Bus/ {line=line+1}END{if(line>1){print serv": virtual server"}else print serv": not a virtual server"}'

...or...

awk -v serv=$i '/Virtual I\/O Bus/ {line=line+1}
END {if(line>1)
print serv": virtual server";else print serv": not a virtual server"}'

Re: awk and else statements

Dennis Handly — Sat, 19 May 2007 01:24:07 GMT

I'm not sure whats wrong. As SPEX says, it works for me if the input has multiple instances of that string.

You may want to remove that ";: as JRF says?

You may also want to use a better awk formating style and not use just one line:
$ |awk -v serv=$i '
/Virtual I\/O Bus/ {line=line+1}
END {
if (line>1) {
print serv": virtual server"
} else {
print serv": not a virtual server"
}
}'

>Clay: First, you don't need your line variable because awk has the built-in NR variable.

Sure it does. line is counting matches, not lines. Of course if the name was called "matches", Clay would be happier. ;-)

Re: awk and else statements

A. Clay Stephenson — Sat, 19 May 2007 09:43:27 GMT

You are correct; I missed the first single quote in the second example. I read all that -v serv=$i/Virtual ... stuff ass the variable actually being passed if so that the line count was unconditional.

Re: awk and else statements

Hein van den Heuvel — Sat, 19 May 2007 14:40:58 GMT

Like for the rest, it works for me.

I guess the is not delivering exactly what you expect.

Hints... try something simpler

|awk '/Virtual/{line++; print line, $0}'

next:

|awk -v serv=$i '/Virtual I\/O Bus/ {line=line+1};END{ print serv, line}'

Those \escaped characters are always tricky.
If there is no risk for false positives, then just replace by a '.' for 'any' character.

Consider this:

$ awk -v serv=$i '/Virtual I.O Bus/{line++} END { not=(line<2)? ":not a" : ":"; print serv not "vi
rtual server"}'

Here I conditionally modify a variable in the print line instead of conditionally selecting the 'right' print line.
Why? Because now the rest of the print statement will be exactly the same. Equally broken or equally correct. Easier to maintain!

Cheers,
Hein.

Re: awk and else statements

Peter Nikitka — Mon, 21 May 2007 11:16:40 GMT

Hi,

Hein's remark is important!
>>
Those \escaped characters are always tricky.
If there is no risk for false positives, then just replace by a '.' for 'any' character.
<<

But don't use '.' in that case but '[/]' like this:
awk '/Virtual I[/]O Bus/ {..

This can always be used as a save 'esacpe' mechanism.

mfG Peter

Re: awk and else statements

Sandman! — Mon, 21 May 2007 11:55:49 GMT

What should be the output of "" if "serv is a virtual server" should it output any lines that have "Virtual I/O Bus" or not?

~thanks

Re: awk and else statements

Dennis Handly — Mon, 21 May 2007 12:39:59 GMT

>Sandman: What should be the output of "" if "serv is a virtual server" should it output any lines that have "Virtual I/O Bus" or not?

I assumed that it outputs more than one. And with that assumption, my awk fragment worked.

Re: awk and else statements

Sandman! — Mon, 21 May 2007 14:23:32 GMT

So does my awk script Dennis but I wanted to clarify whether the author of the thread had made a typo in... if(line>1) ...where the intention was... if(line>0).

~cheers

Re: awk and else statements

lawrenzo_1 — Tue, 22 May 2007 03:20:27 GMT

ok thanks all,

looks like I forgot {} for the else statement.

will add this to my never ending notes.

Chris

Re: awk and else statements

lawrenzo_1 — Tue, 22 May 2007 03:28:16 GMT

Thanks again all,

sandman you are correct line should be >0 and not >1.

all examples will help in the future.

Cheers

Chris.

Re: awk and else statements

Dennis Handly — Tue, 22 May 2007 03:48:31 GMT

>line should be >0 and not >1.

If this is the case, there is no need to count them up. Just do:
/Virtual I\/O Bus/ { print serv ": virtual server"; exit}
END { print serv ": not a virtual server"}

You can also make it simpler by just using grep:
| grep -q "Virtual I/O Bus"
if [ $? -eq 0 ]; then
echo "$i: virtual server"
else
echo "$i: not a virtual server"
fi

Re: awk and else statements

lawrenzo_1 — Tue, 22 May 2007 03:51:21 GMT

Thanks Dennis,

I am pretty handy with shell scripting so I am attempting to learn awk / sed and later on perl ....

but thanks for the examples.

Chris