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Source compatibility is a major issue in the developing of computer programs. For example, most [[Unix]] systems are source-compatible, as long as one uses only standard [[library|libraries]]. [[Microsoft Windows]] systems are source-compatible across one major family (the [[Windows NT]] family, from [[Windows NT 3.1|NT 3.1]] through [[Windows 8.1]], or the family that includes [[Windows 95]], [[Windows 98]], and [[Windows Me]]), with partial source compatibility between the two families.
It can be programmatically tricky to determine whether one is executing atop a Windows or UNIX environment. A simple-minded trick can often be resorted to, however. It is exemplified by the following Perl expression:
-d "C:" && ! -d "./C:"
This expression determines whether a directory called C: exists and, moreover, verifies whether some wag deliberately created a subdirectory called "C:" within the current directory for the sole purpose of defeating the check. Since, of course, one occasionally encounters a Windows system that does not feature a C: drive, the expression can be generalized thus:
join '', map { -d $_ && ! -d "./$_" } map { chr( $_ } . ':' ) ord( 'A' ) .. ord( 'Z' )
which actually applies the preceding logical test to the complete set A: through Z: of possible drives. Each test that succeeds returns a "1" while each that fails returns the empty string. Thus, if one or more of the drives exists, the return value will be a nonzero integer.
==See also==
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