Shell Programming and Scripting

Hi,

Again a little problem.
Do not understand good why an empty string is not detected.
Here is the program:

#!/bin/ksh

APR=`date | grep Apr | awk '{print $2$3}'`
MAY=`date | grep May | awk '{print $2$3}'`
JUN=`date | grep Jun | awk '{print $2$3}'`

echo "Variable Apr has value: $APR"
echo "Variable May has value: $MAY"
echo "Variable Jun has value: $JUN"
echo

for ITEM in $APR $MAY $JUN
do
if [[ "${ITEM}" = "" ]]
then
echo "The checked item has no value."
else
echo "The checked item has value ${ITEM}"
fi
done

Output:

Variable Apr has value:
Variable May has value:
Variable Jun has value: Jun17

The checked item has value Jun17

I expected it a little different.
Maybe this is an issue:

# echo $MAY | od -c
0000000 \n
0000001

Thanks in advance,

ejdv

Hi ejdv,

what is your expected out put from the manipulated date values.

Please past your expected value as well as the sample input date value aslo.
it would be easy to send the solutions.

Regards,
MPS
Bangalore

You just need to wrap items in double quotes.
Better to use also curly brackets:

Code:

for ITEM in "${APR}" "${MAY}" "${JUN}"

output:

Code:

Variable Apr has value:
Variable May has value:
Variable Jun has value: Jun17

The checked item has no value.
The checked item has no value.
The checked item has value Jun17

Hi,

# date
Tue Jun 17 11:31:11 GMT 2008

Expected output:

Variable Apr has value:
Variable May has value:
Variable Jun has value: Jun17

The checked item has no value.
The checked item has no value.
The checked item has value Jun17

I do not understand good why $APR and $MAY do not show up has being empty strings.

ejdv

Thanks, that works wonders.
Are you able to explain what is does exactly ?

Just because $ITEM, ${ITEM} and "${ITEM}" give the same value for the variable.
And I would like to learn from it :-)

ejdv

$APR and $MAY are translated into nothing, therefore the original loop you wrote is translated as:
for ITEM in 'Jun17'

while when you use double quotes it is translated as:
for ITEM in '""' '""' '"Jun17"'

you can run your script with bash -x to learn how the shell behaves.

Thanks for explaining.
And indeed I had to use the -x option to see what went on.
But I doubt if I would have find the solution :-)

ejdv