Perl Debugger

Perl Debugger is the interactive source debugger built into Perl, best suited to developers tracing scripts written in the language. It brings breakpoints, stepping, and value inspection into the Perl runtime, with clear limits around compile-time execution and native extensions.

Overview

Start a script with Perl’s -d flag: Perl adds source information and loads the debugger library, so no separate debugger program is required. The script must compile successfully before debugging can begin. That makes Perl Debugger a practical first choice for investigating ordinary Perl execution, especially when keeping the workflow inside the language runtime matters.

Key features

At the prompt, users can inspect source, set conditional breakpoints, view stack backtraces, and change variable values. The s command steps into a subroutine; n runs over the call to the next statement. Tracing adds another way to follow execution. These controls are well suited to narrowing down behavior in a Perl script, though compile-time executable statements such as BEGIN, UNITCHECK, CHECK, and use are not stopped by the debugger. Some compile-time code can be traced with AutoTrace.

A global watch expression pauses execution when its value changes and reports the old and new values. The x command evaluates an expression and recursively pretty-prints nested data structures; package variables can also be displayed. Lexical-variable inspection requires PadWalker version 0.08 or higher, a meaningful extra dependency for developers whose debugging depends on lexical state.

Commands the debugger does not recognize are evaluated as Perl code in the current package, giving Perl users a direct way to probe the running program. Options can be set at the prompt, through PERLDB_OPTS, or in .perldb customization files. Since those files can run arbitrary commands, they must be owned by the superuser or current user and writable only by their owner. The LineInfo option can connect to client editors or visual debuggers, with vi, emacs, and ddd among the examples. A GUI route is also described through Devel::ptkdb using perl -d:ptkdb. Full command-line editing requires Term::ReadKey and a Term::ReadLine module.

Threaded programs can be debugged with -dt, but that invocation is experimental. The debugger also cannot show stack-frame information or debug functions that Perl did not compile, including C or C++ extension functions; workflows that cross into native code will need another approach. It does not currently work with Perl’s -W switch.

Pricing

Perl Debugger is free at free. The plan is included with Perl and supports Perl debugging, with the requirement that the program compile correctly first. There is no separate debugger purchase or trial to weigh; its practical cost is the optional modules needed for lexical inspection or full command-line editing.

Platforms

The debugger is available wherever Perl is available in the supported platform set: Linux, macOS, and Windows. Perl is included on Unix/Linux and macOS, while Strawberry Perl provides a Windows option.

Who it's for

Choose it if you write Perl and want an included debugger for stepping through scripts, setting conditional breakpoints, watching global values, and inspecting data without installing a separate debugger. It is less suitable if your work centers on compile-time code, native extension functions, or the -W switch. Learners can turn to learn.perl.org and the Perl Community for help.

Pros and cons

• Included with Perl and free: the -d flag loads the debugger without a separate debugger installation.
• Useful runtime controls: stepping, conditional breakpoints, global watches, backtraces, and nested-value display support focused script investigation.
• Flexible customization: options and editor connections can be configured, with an optional GUI path through Devel::ptkdb.
• Extra modules for some workflows: PadWalker is needed to inspect lexical variables, while full command-line editing needs Term::ReadKey and a Term::ReadLine module.
• Boundaries for mixed-language debugging: native extension functions lack debugger stack-frame information, and compile-time statements are not stopped.
• Experimental threaded mode and switch incompatibility: -dt is marked experimental, and the debugger does not work with -W.

Alternatives

Browse more debuggers if Perl Debugger’s language focus or runtime limits do not fit. Choose LLDB for a free, open-source debugger across Android, iOS, Linux, macOS, and Windows. IDA Pro is a paid option with a free tier for x86-32 and x86-64 disassembly and two cloud-based decompilers; its Pro Essential plan costs 1099.00 USD. PonyDebugger is a free option with an iOS client and gateway server. pyOCD is a free, Apache 2.0 open-source project. Choose Black Magic Debug for JTAG/SWD debugging of embedded microcontrollers when you have compatible probe hardware and a suitable toolchain. FlowStorm is free and open source. GDB is a free debugger whose source code is available under the GNU General Public License. OpenOCD is free open-source software distributed through operating-system packages or source code.

Verdict

Perl Debugger is the right choice for Perl developers who want a free, built-in way to inspect and control script execution. Its runtime stepping, breakpoints, watches, and data inspection cover the core debugging loop without a separate debugger program. Look elsewhere when you need stack-frame details for C or C++ extension functions, need to stop at compile-time statements, or depend on Perl’s -W switch.