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Top Forums Shell Programming and Scripting Korn expr substr fails for non-numeric value Post 302382816 by bakunin on Friday 25th of December 2009 11:55:00 PM
Old 12-26-2009
In AIX (including 5.3) /bin/ksh is a ksh88, whereas /bin/ksh93 is a ksh93. The substr()-function in the form "${var:start:length}" is only implemented in ksh93.

cfajohnsons observation is correct in a very general way: using ksh93-functions always runs the risk of getting less portable. On the other hand: using an external tool (expr, sed, awk, whatever) to trim the variables content is expensive in terms of system calls. I would like to offer the following solution to this problem, which which work in every ksh.version:

Code:
sub1=${DDNAME%${DDNAME#?????}}
sub=${sub1#???}

The first line extracts the first 5 characters from the string $DDNAME, the second statement extracts the last 2 from these 5 characters, effectively giving the substring starting at pos 4, length 2. Because this is done completely in the shell and without calling an external program it shoulld be by far faster than any solution based on such a program.

cfajohnson already explained how this can be tested for being an integer or not.

I hope this helps.

bakunin
 

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test(1) 						      General Commands Manual							   test(1)

Name
       test - test conditional expression

Syntax
       test expr
       [ expr ]

Description
       The  command  evaluates the expression expr.  If the value of expr is true, the command returns a zero exit status; otherwise, it returns a
       nonzero exit status.  The command also returns a nonzero exit status if no arguments are specified.

Options
       The following primitives are used to construct expr:

       -r file		   Tests if the file exists and is readable.

       -w file		   Tests if the file exists and is writable.

       -f file		   Tests if the file exists and is not a directory.

       -d file		   Tests if the file exists and is a directory.

       -s file		   Tests if the file exists and has a size greater than zero.

       -t [ fildes ]	   Tests if the open file, whose file descriptor number is fildes (1 by default), is associated with a terminal device.

       -z s1		   Tests if the length of string s1 is zero.

       -n s1		   Tests if the length of the string s1 is nonzero.

       s1 = s2		   Tests if the strings s1 and s2 are equal.

       s1 != s2 	   Tests if the strings s1 and s2 are not equal.

       s1		   Tests if s1 is not the null string.

       n1 -eq n2	   Tests if number1 equals number2.

       n1 -ge n2	   Tests if number1 is greater than or equal to number2.

       n1 -gt n2	   Tests if number1 is greater than number2.

       n1 -le n2	   Tests if number1 is less than or equal to number2.

       n1 -lt n2	   Tests if number1 is less than number2.

       n1 -ne n2	   Tests if number1 is not equal to number2.

       These primitives can be combined with the following operators:

       !expr		   Negates evaluation of expression.

       expr -a expr	   Tests logical and of two expressions.

       expr -o expr	   Tests logical or of two expressions.

       ( expr... )	   Groups expressions.

       The -a operator takes precedence over the -o operator.  Note that all the operators and flags are separate  arguments  to  Note	also  that
       parentheses are meaningful to the Shell and must be escaped.

See Also
       find(1), sh(1), test(1sh5)

																	   test(1)
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