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While-read and if-elif

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# 1  
Old 09-13-2012
While-read and if-elif
Hi there, new to this forum and I recently encounter this problem:

I tried to use if-elif loop in a while-read loop, something like this:
Code:
#!/bin/bash
while read myline1 myline2
do
if [ '$myline1 > '$myline2' ]; then
  echo "Successful!"
elif [ '$myline1 < '$myline2' ]; then
  echo "Failed"
fi
done < $1

Input file looks like this:
Code:
200 100
100 200

But the results that I got was:
Code:
Successful!
Successful!

It doesn't seems to read the elif condition. Can anyone help?

Thanks!
Ken
Last edited by Franklin52; 09-13-2012 at 06:35 AM.. Reason: Please use code tags for data and code samples
# 2  
Old 09-13-2012
Quote:
Originally Posted by kennethtls
#!/bin/bash
while read myline1 myline2
do
if [ '$myline1 > '$myline2' ]; then
echo "Successful!"
elif [ '$myline1 < '$myline2' ]; then
echo "Failed"
fi
done < $1
Try with this..

Code:
#!/bin/bash
while read myline1 myline2
do
if [ '$myline1' > '$myline2' ]; then
  echo "Successful!"
elif [ '$myline1' < '$myline2' ]; then
  echo "Failed"
fi
done < $1

# 3  
Old 09-13-2012
1) Doublequote your variables inside the tests; single quotes prevent variable expansion (and, btw, one quote is missing).
2) use -lt and -gt for numerical comparison; < and > do a string comparison.
# 4  
Old 09-13-2012
Quote:
Originally Posted by pamu
Try with this..

Code:
#!/bin/bash
while read myline1 myline2
do
if [ '$myline1' > '$myline2' ]; then
  echo "Successful!"
elif [ '$myline1' < '$myline2' ]; then
  echo "Failed"
fi
done < $1

Hi there, thanks for the help but I don't think is the issue with the single quote, I tried adding the single quote but has the same result.

Possible that there is other dependencies related?
# 5  
Old 09-13-2012
To add to RudiC's advice:
1) use [[...]]/((...))constructs instead of [...]. That way, there is no need to double-quote the variables.
# 6  
Old 09-13-2012
You're using the wrong quotes and they aren't matched. And the < and > operators don't exist in the test utility; you're performing redirections in the operands given to test. Try:
Code:
#!/bin/bash
while read myline1 myline2
do
if [ "$myline1" -gt "$myline2" ]; then
echo "Successful!"
elif [ "$myline1" -lt "$myline2" ]; then
echo "Failed"
fi
done < $1

# 7  
Old 09-13-2012
Quote:
Originally Posted by RudiC
< and > do a string comparison.
Hi Rudic,

I am not able to understand how we can use < and > signs for string comparison....????
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