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Checking for null condition in a UNIX variable

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# 1  
Old 07-01-2013
Checking for null condition in a UNIX variable
i have this code
Code:
for i in `cat sql_output.txt`
do
-- some script commands
done

sql_output.txt has 1 column with employee_ids
If the sql_output.txt is null then the do loop should not execute.
How can i implement this.

Code:
for i in `cat sql_output.txt`
If i is null or empty
then 
echo "no ids to execute"
else
do
-- some script commands
done


i should be checked for null condition only once..at the very beginning if is not null then it for loop should be executed
# 2  
Old 07-01-2013
What shell do you use? Read its man page!

You will find sth like [ ! -s sql_output.txt ] will do what you need.
# 3  
Old 07-01-2013
Quote:
Originally Posted by RudiC
What shell do you use? Read its man page!

You will find sth like [ ! -s sql_output.txt ] will do what you need.
i am using bash.
-s checks if file is emty or not?
# 4  
Old 07-01-2013
Code:
cat sql_output.txt|while read line
do
  typeset -i charCount=`echo $line|wc -c`
  if [[ $charCount -eq 1 ]]; then
    echo "no ids to execute"
  else
    echo "some scipts command"
  fi
done

Last edited by Scott; 07-01-2013 at 07:27 AM.. Reason: Please use code tags
# 5  
Old 07-01-2013
Quote:
Originally Posted by rafa_fed2
i am using bash.
-s checks if file is emty or not?
Again, read the man bash:
Quote:
-s file
True if file exists and has a size greater than zero.
This User Gave Thanks to RudiC For This Post:
rafa_fed2
# 6  
Old 07-01-2013
Quote:
Originally Posted by zzavilz
Code:
cat sql_output.txt|while read line
do
  typeset -i charCount=`echo $line|wc -c`
  if [[ $charCount -eq 1 ]]; then
    echo "no ids to execute"
  else
    echo "some scipts command"
  fi
done

Thanks zzav for the reply.But Rudi solution seems more simpler than you .Smilie
I implemented that

what does while read line and typeset do in your code.

i think your code will be useful where there are some lines prenet along with ids.
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