To run script in debug mode you should add -d option in the command line:

$perl -d script.pl

If t is specified, it indicates to the debugger that threads will be used in the code being debugged:

$perl -dt script.pl

Additional info at perldocperlrun (opens new window)

$perl -d:MOD script.pl runs the program under the control of a debugging, profiling, or tracing module installed as Devel::MOD.

For example, -d:NYTProf executes the program using the Devel::NYTProf profiler (opens new window).

See all available Devel modules (opens new window) here

Recommended modules:

• Devel::NYTProf (opens new window) -- Powerful fast feature-rich Perl source code profiler
• Devel::Trepan (opens new window) -- A modular gdb-like Perl debugger
• Devel::MAT (opens new window) -- Perl Memory Analysis Tool
• Devel::hdb (opens new window) -- Perl debugger as a web page and REST service
• Devel::DebugHooks::KillPrint (opens new window) -- Allows to forget about debugging by print statement
• Devel::REPL (opens new window) -- A modern perl interactive shell
• Devel::Cover (opens new window) -- Code coverage metrics for Perl