Variable IF statement in awk

Shell Programming and Scripting
1

I have multiple requirements to run data extracts (with the same basic requriement / resulsts) however the parameters of the extracts change with each request. To help make life easier I am writing a script where the parameters for the specific request are set at the start and then used as needed.
HOWEVER I am having problems with the awk portion of the script.

To simplify matters here is test data and script to explain the problem.

data file as follows (test)

1 a
2 b
3 c
4 d

in this instance I want to output record 3 c

script as follows:

parm='&& ($2=="c")';
cat test | awk -v parm="$parm" '{if ((1==1) parm) {print $0}}'

this is outputting the entire file and not just the 3rd record
(note: the (1==1) is a failsafe incase there is no parameter passed)

2

Why you need a fail-safe? How about:

parm="c"

awk -v p=$parm '{
 if(p=="") { print $0; }        # If p is not defined print all records in file.
 else { if($2==p) print $0 }    # If p is defined, then print only that specific record.
}' file

Also note that the cat command is useless, awk is capable of reading the file by itself.

3

hi bipinajith
my problem is that the filter field changes with each request. next time it could be column 1 or column 10. I need the whole statement to be flexible.

4

Ok, then how about using a variable for column:-

col=2
parm="c"

awk -v c=$col -v p=$parm '{if(c=="") { print $0; }else { if($c==p) print $0 }}' file
5

[quote=bipinajith;302754221]
Why you need a fail-safe? How about:

parm="c"

awk -v p=$parm ...
[...]

As a side note:
 - in most cases it's safer to quote $param:, just in case the value of $param contains spaces or other shell special characters 
and shell word/field splitting is enabled (default for most shells, excluding zsh):

$ param='a b'
$ # this one fails
$ awk -v p=$param 1 < /dev/null
awk: cmd. line:1: fatal: cannot open file `1' for reading (No such file or directory)
$ # this one succeeds 
$ awk -v p="$param" 1 < /dev/null
$
1 Like
6

Actually, this could work. awk uses the first parameter - after all option have been evaluated - as the program if nothing else ist supplied with e.g. the -f or -e option:

$ parm="NR>1 && \$2==\"c\""
$ echo $parm
NR>1 && $2=="c"
$ awk "$parm" file
3 c

Not sure though if it makes sense to supply variables like this...

1 Like
7

Thank you bipinajith - while that does work I think I may have oversimplified my problem. This awk statement is only one statement in a very complex script, and my parameters are not as simple as $2=c. In one case it may be ($2=='c' || $2==a) && $3=='y'... in another case it may be a completely different set of fields.

My question basically was can you pass full portions of if statment (including all syntax) to awk?? if not I will just have to change the script each time.

RudiC - that may work... thanks will play around with it and see where I get :smiley:

---------- Post updated at 01:46 AM ---------- Previous update was at 01:04 AM ----------

THANKS Rudi this works beautifully....

parm1=" && (\$2==\"c\" || \$2==\"a\")";
parm2="";
echo "$parm1";
echo "$parm2";
cat test | awk '{if ((1==1)'"$parm1""$parm2"') {print $0}}'

results:

 && ($2=="c" || $2=="a")
1       a
3       c

the reason I am keeping the cat is becuase I am doing various sorts and joins etc with the data prior to the awk statement.
The 1==1 means I don't have to check for the parm1 and parm2 variables being blank. even if they are blank the statement still works (will output all rows).