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'''-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
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