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Advanced Perl Programming

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Previous: B.5 ObjectsAppendix B
Syntax Summary
Next: B.7 Exception Handling

B.6 Dynamic Behavior

  1. Symbolic references:

    $i = "foo";
    $$i = 10;             # Sets $foo to 10
    ${"i"} = 10;          # Sets $foo to 10
    &$i();                # Calls foo();
    push (@$i, 10, 20);   # Pushes 10,20 into @foo
  2. Run-time expression evaluation:

    while (defined($str = <STDIN>)) {
        eval ($str);
        print "Error: $@" if $@;

    This is a tiny Perl shell, which reads standard input, treats $str as a small program, and puts the compilation and run-time errors in $@.

  3. Dynamic substitutions. Use the /e flag for the s/// operator, to specify an expression instead of a pattern:

    $l = "You owe me 400+100 dollars";
    $l =~ s/(\d+)\+(\d+)/$1 + $2/e;
    print $l; # prints "You own me 500 dollars"
  4. Module and object method invocations (see also #20 and #21):

    $modulename->foo(); # Calls foo() in the module indicated by
                        # $modulename

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