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Help on string comparison in bash script...

Hello All

I'm a mediocre level bash scripter. Following code is making me crazy. I cant understand what I'm doing wrong. I just want to make sure the parameter passed to script is either '264' or '265'.

The problem is in first if statement. The second works fine. Whats wrong in first one?

Code:

#!/bin/bash



echo "Type 1:"

if [[ "$1" != "264" || "$1" != "265" ]] ; then

    echo "Parameter should be 264 or 265"

else

    echo "Correct"

fi



echo "Type 2:"

if [[ "$1" == "264" || "$1" == "265" ]] ; then

    echo "Correct"

else

    echo "Parameter should be 264 or 265"

fi

Result is like this:

Code:

$ ./strcomp.sh abc

Type 1:

Parameter should be 264 or 265

Type 2:

Parameter should be 264 or 265



$ ./strcomp.sh 264

Type 1:

Parameter should be 264 or 265

Type 2:

Correct



$ ./strcomp.sh 265

Type 1:

Parameter should be 264 or 265

Type 2:

Correct

Why != in first if statement comparsion is not working?

Thanks

I think you need && in that first statement, not ||.

Suppose $1 is 254. Then the first half of the statement is false. But the second half is true because 254 != 255. Similarly if $1 is 255, the first half becomes true (255 != 254) but the second half becomes false.

Since you have used or logic, either half-statement being true will give an error message. With and logic, you will only get an error if both halves are true.

Quote:

Originally Posted by hazel (Post 5605687)

Hmmm... now I got it. Thanks for the explanation.