Data commit

Task/Undefined-values/Perl/undefined-values.pl

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+#!/usr/bin/perl -w
+use strict;
+
+# Declare the variable. It is initialized to the value "undef"
+our $var;
+
+# Check to see whether it is defined
+print "var contains an undefined value at first check\n" unless defined $var;
+
+# Give it a value
+$var = "Chocolate";
+
+# Check to see whether it is defined after we gave it the
+# value "Chocolate"
+print "var contains an undefined value at second check\n" unless defined $var;
+
+# Give the variable the value "undef".
+$var = undef;
+# or, equivalently:
+undef($var);
+
+# Check to see whether it is defined after we've explicitly
+# given it an undefined value.
+print "var contains an undefined value at third check\n" unless defined $var;
+
+# Give the variable a value of 42
+$var = 42;
+
+# Check to see whether the it is defined after we've given it
+# the value 42.
+print "var contains an undefined value at fourth check\n" unless defined $var;
+
+# Because most of the output is conditional, this serves as
+# a clear indicator that the program has run to completion.
+print "Done\n";