then is not a keyword in perl, but you seem to have the basic idea. You probably want to look at the man page for exit, which you can pass an exit code to.

Here's one way to do it. You could write the main algorithm as a subroutine, then have that subroutine return either 1 (failure) or 0 (success). See What is true and false in Perl? for information about how Perl understands "true". The basic program logic for this strategy looks like this:

if (subroutine()) { # if the return value of subroutine is "true" (see
+ reference above)
   exit 0; # success
} else {
   exit 1; # failure
}
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Alternately, you could use a neat trick: have the *subroutine* return 0 for success and 1 for failure, and just call:

exit subroutine();
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Which will execute the subroutine and exit with the value the subroutine returns.

Last, but certainly not least, perl provides the die function, which returns an error status along with a (definable) error message. See die for more details on that, but it is the preferred way of raising exceptions in perl.

HTH!

perl -e 'print "How sweet does a rose smell? "; chomp ($n = <STDIN>); 
+$rose = "smells sweet to degree $n"; *other_name = *rose; print "$oth
+er_name\n"'
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