Checking for null condition in a UNIX variable

Shell Programming and Scripting
1

i have this 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.

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

What shell do you use? Read its man page !

You will find sth like [ ! -s sql_output.txt ] will do what you need.

3

i am using bash.
-s checks if file is emty or not?

4 
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
5

Again, read the man bash :

1 Like
6

Thanks zzav for the reply.But Rudi solution seems more simpler than you .:slight_smile:
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.