Shell Programming and Scripting

01 and 1 are numerically equal, so should you be comparing numbers or strings? ''01" is not equal to "1", or does ksh not distinguish the difference?

On the same hand, this:

MNTH=$MNTH-01

seems the same as:

MNTH=$MNTH-1

I would think the leading 0 is silently dropped from the equation.

The leading zero can be an issue. [ $MNTH = 01 ] will be true is MNTH is 01 but it will be false if MNTH is just 1. Instead of = you can use -eq like this: [ $MNTH -eq 1 ] and this is an integer compare rather than a string compare. But with many version of ksh a leading zero indicated an octal number so 09 is not a valid number with these versions. This is required by Posix so it may become more common.

I did a little experimenting and these seem to evaluate to true:

Code:

#!/usr/bin/ksh
((MNTH = 1))
MNTH=$(printf "%02d" $MNTH)
#echo $MNTH
if [ MNTH -eq "01" ]; then
   echo $MNTH
fi
if [ MNTH -eq "1" ]; then
   echo $MNTH
fi
if [ "$MNTH" == 01 ]; then
   echo $MNTH
fi
if [ $MNTH == 01 ]; then
   echo $MNTH
fi
if [ $MNTH = 01 ]; then
   echo $MNTH
fi

Now I have never written a single line of ksh before this so I am not sure in what context those test conditions are being evaluated.

Yeah but 1 in base 10 equals 1 in base 8. Try it with 09 to see if your ksh treats leading zeros as indicating octal. Also post your os version.

These all seem to evaluate to true:

Code:

#!/usr/bin/ksh
((MNTH = 9))
MNTH=$(printf "%02d" $MNTH)
echo $MNTH
if [ MNTH -eq "09" ]; then
   echo $MNTH
fi
if [ MNTH -eq "9" ]; then
   echo $MNTH
fi
if [ "$MNTH" == 09 ]; then
   echo $MNTH
fi
if [ $MNTH == 09 ]; then
   echo $MNTH
fi
if [ $MNTH = 09 ]; then
   echo $MNTH
fi

I 'm testing on Linux but I don't know the version number.

Thank you all for your help it is much appreciated!

Here is my summation of things, please feel free to correct me if I am wrong.
========================================================
The format of $MNTH was `date +%m` which adds the "0"

The calculation with the "0" and without the "0" (01-01, 01-1, 1-1)
Mathmatical calculations will always drop the "0", which to me is a known, I just did not know if unix would hold the "0" in place once formated. (it does not )

With the help of Jim_M, I was able to reformat the date and put the "0" back in place.
Code:
However, this then provided with the problem - when $YEAR = "2009" and $MNTH = "01", my if statement outputed 00/2008 (which is obviously incorrect )
So.....with the help of Perderabo and his correction....below,
Things seem to work know, I tested the following $MNTH and $YEAR values
01/2009 returned as 12/2008
12/2008 returned as 11/2008
10/2008 returned as 09/2008
02/2008 returned as 01/2008
03/2008 returned as 02/2008

Thank you all for your help and support, I think I just felt another ripple on my brain form!

Here is what the if statement looks like now
if [ $MNTH != 01 ]
then
(( MNTH=$MNTH-01 ))
MNTH=$(printf "%02d" $MNTH)
YEAR=$YEAR
else
if [ $MNTH = 01 ]
then
MNTH=12
(( YEAR=$YEAR-1 ))
fi
fi


cml2008