This has little to do with Perl and everything to do with that & is a special character in your shell. You will need to use quotes to prevent your shell from interpreting the code:

perl UserScenarioDesc.pl '&get_user_scenario_desc("http://some_link/XY
+Z.html","testdare/UserScenarioDAREtestCkmadm")'
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But your program makes little sense and it does not use the passed parameters. Read perlvar to find about @ARGV as where the shell passes parameters to Perl. Most likely you just want to use the following in your program:

get_user_scenario_desc(@ARGV);
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