Awk conditional inside bash while loop

Question

I am trying to make a while loop that goes through a text file line by line, tests whether a field is blank using Awk, then does an action based on whether that condition is true or false.

The input file is this:

$ cat testarr.csv
cilantro,lamb,oranges
basil,,pears
sage,chicken,apples
oregano,,bananas
tumeric,turkey,plums
pepper,,guavas
allspice,goose,mangos

My expected output is:

this_is_one_iteration
ItIsNotBlank
this_is_one_iteration
ItIsBlank
this_is_one_iteration
ItIsNotBlank
this_is_one_iteration
ItIsBlank
this_is_one_iteration
ItIsNotBlank
this_is_one_iteration
ItIsBlank
this_is_one_iteration
ItIsNotBlank

based on Using 'if' within a 'while' loop in Bash and similar threads, I did this:

#!/bin/bash

error=ItIsBlank
success=ItIsNotBlank
while read LINE; do
echo this_is_one_iteration
QZ1=$(awk -F "," '{print (!$2)}')
if [[ $QZ1==0 ]] ; then
    echo $error
else
    echo $success
fi
done < testarr.csv

which gave me:

$ bash testloop.sh
this_is_one_iteration
ItIsBlank

So it doesn't even seem to be iterating through the file. However, if I take out the conditional, it iterates just fine.

#!/bin/bash

error=ItIsBlank
success=ItIsNotBlank
while read LINE; do
echo this_is_one_iteration
done < testarr.csv

gives:

$ bash testloop.sh
this_is_one_iteration
this_is_one_iteration
this_is_one_iteration
this_is_one_iteration
this_is_one_iteration
this_is_one_iteration
this_is_one_iteration

also, the conditional seems to work OK when not using awk:

QZ1=test
while read LINE; do
echo this_is_one_iteration
if [[ $QZ1=="test" ]] ; then
    echo It_worked
fi
done < testarr.csv

Gives me:

$ bash testloop.sh
this_is_one_iteration
It_worked
this_is_one_iteration
It_worked
this_is_one_iteration
It_worked
this_is_one_iteration
It_worked
this_is_one_iteration
It_worked
this_is_one_iteration
It_worked
this_is_one_iteration
It_worked

So you want to do this in bash script or an Awk command? — Inian
– Inian, Commented Oct 9, 2017 at 17:25
I don't care. I just need to test whether a field is blank and then do bash stuff based on that. Why doesn't it work to pass the output of awk to bash? — Stonecraft
– Stonecraft, Commented Oct 9, 2017 at 17:28
the proper line is with 3 fields and the improper ones have less than 3? — Inian
– Inian, Commented Oct 9, 2017 at 17:30
Not necessarily, although in this specific example that happens to be true. So no, simply testing the number of fields in the line will not help me. — Stonecraft
– Stonecraft, Commented Oct 9, 2017 at 17:38

abhishek phukan · Accepted Answer · 2017-10-09 17:56:29Z

1

Your script is correct except for a minor error. Add echo $LINE and pipe it to the awk statement. Awk in your script has no input to work on.

#!/bin/bash 

error=ItIsBlank
success=ItIsNotBlank
while read LINE; do
echo this_is_one_iteration
QZ1=$(echo $LINE|awk -F "," '{print (!$2)}')
if [[ $QZ1 -eq 0 ]] ; then
 echo $error
else
 echo $success 
fi
done < testarr.csv

When i run the script now:

[ec2-user@ip check]$ ./script.sh
this_is_one_iteration
ItIsBlank
this_is_one_iteration
ItIsBlank
this_is_one_iteration
ItIsBlank
this_is_one_iteration 
ItIsBlank
this_is_one_iteration
ItIsBlank
this_is_one_iteration
ItIsBlank
this_is_one_iteration
ItIsBlank

Hope this resolves your issue.

edited Oct 9, 2017 at 17:56

answered Oct 9, 2017 at 17:46

abhishek phukan

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3 Comments

Stonecraft Over a year ago

Thanks, that almost worked, but the == operator didn't work in this context, instead I used -eq and that gave the expected output

abhishek phukan Over a year ago

Glad it worked . Please Close the thread if the issue is resolved . I have edited the answer in case someone else comes across the same problem

Gordon Davisson Over a year ago

The problem wasn't == vs. -eq, it was that you need spaces around the operator. == (or =) test for string equality, -eq tests for numeric equality. In this case, either would work.

RomanPerekhrest · Accepted Answer · 2017-10-09 17:44:55Z

0

tests whether a field is blank using Awk

I suppose, it can be achieved with single awk process:

awk -F, '{ print "this_is_one_iteration"; f="Not"; 
           for(i=1;i<=NF;i++) if($i=="") { f="";break }; printf "ItIs%sBlank\n",f }' testarr.csv

The output:

this_is_one_iteration
ItIsNotBlank
this_is_one_iteration
ItIsBlank
this_is_one_iteration
ItIsNotBlank
this_is_one_iteration
ItIsBlank
this_is_one_iteration
ItIsNotBlank
this_is_one_iteration
ItIsBlank
this_is_one_iteration
ItIsNotBlank

answered Oct 9, 2017 at 17:44

RomanPerekhrest

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1 Comment

Stonecraft Over a year ago

But will this allow the result of the truth test to execute bash code? My point wasn't to print "ItIsBlank", I was just echoing that as a test of ability to send it to bash.

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