do will "do" this.
Two files, one named "priv" and one named "unpriv". Their contents:
priv:

  sub priv {
    print "Privileged\n";
  }
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unpriv:

  sub priv {
    print "Unprivileged\n";
  }
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Now, in your main program, you can:

  #!/usr/bin/perl
  do "unpriv";
  priv();
  do "priv";
  priv();
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Which when run:

  > perl main
  Privileged
  Unprivileged
  >
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