UNIX for Dummies Questions & Answers

In AIX, why is it variable VAR becomes true in the condition despite VAR was unassigned and not equal to 1?
In Linux, it was traced as an error as VAR is not declared as variable and expecting an integer as argument.

one.sh

Code:

VAR=1

if [ VAR -eq 1 ]; then
   echo "One"
fi

if [ $VAR -eq 1 ]; then
   echo "Two"
fi

AIX Output:

Code:

One
Two

Linux Output:

Code:

./one.sh: line 4: [: VAR: integer expression expected
Two

It sounds like you already know the $ is left off the first VAR, that you intentionally left $ off.

Well, the Linux behavior is correct, in the sense that it detects the syntax error. -eq implies a number comparison. The string "VAR" is not a number.

I have no idea why the AIX version doesn't figure out there is a problem. Personally, I wouldn't waste any time trying to figure it out, unless you could look at the source code, except to report it as a bug.

Seems AIX is not that strict. I just recreate the scenario and the actual script is used for deleting old files and need to justify why script still works even though VAR is unassigned.(but sometimes it doesn't because files were not deleted).

Running in verbose, In condition#1, VAR -eq 1 was evaluated as true. VAR in condition#2 is assigned since variable is correctly used.

Code:

+ [ VAR -eq 1 ]
+ echo One
One

if [ $VAR -eq 1 ]; then
   echo "Two"
fi
+ [ 1 -eq 1 ]
+ echo Two
Two

Yes, AIX is apparently not that strict.

Once you have nonsense syntax, like VAR which is just a string, all bets are off, and no use trying to figure out why it might work under some apparently lax environment. It is quite odd that AIX does not detect an error.

This is not an OS thing. Which shell are you using? Mention the version too.

I'm using AIX and /bin/sh shell.

uname -a: AIX strebla26 1 6 00CB6E4D4C00
oslevel: 6.1.0.0