Perl Debugger

Overview

Perl Debugger is an interactive source debugger invoked from Perl itself, best suited to developers tracing scripts and inspecting runtime state. It is a practical, no-cost choice for Perl code that compiles, but it is not a debugger for every phase of execution or for native extension code.

Key features

Run a script with Perl’s -d flag to load the debugger alongside the source information Perl inserts. From the prompt, developers can inspect source, view stack backtraces, change variable values, and set conditional breakpoints. The s command enters subroutine calls; n advances past them to the next statement. Tracing is also supported. This gives Perl developers useful control without a separate debugger program, though debugging cannot begin until the code compiles correctly.

Global watch expressions pause execution when a watched value changes and show its previous and new values. The x command evaluates an expression and recursively prints nested data, while package variables can be displayed. Lexical-variable inspection requires PadWalker version 0.08 or higher, a meaningful extra requirement for developers whose investigations depend on lexical state.

Unrecognized commands are treated as Perl code in the current package, making the prompt flexible for users comfortable with the language. Options can be set interactively, through PERLDB_OPTS, or in .perldb files. Because those files can execute arbitrary commands, they must be owned by the superuser or current user and writable only by their owner. Full command-line editing requires Term::ReadKey and a Term::ReadLine module. The LineInfo option can connect with editors or visual debuggers such as vi, emacs, and ddd; a GUI debugging route is also documented through Devel::ptkdb.

Pricing

Perl Debugger costs nothing and is included with Perl. There is no paid tier or free trial; the important qualification is functional rather than commercial: the program must compile before the debugger can work. Threaded programs can be invoked with -dt, but threaded debugging is experimental.

Platforms

Perl Debugger is available on Linux, macOS, and Windows through Perl. Perl is included on Unix/Linux and macOS, while Strawberry Perl provides a Windows option. Its debugger is part of the Perl environment rather than a standalone application.

Who it's for

This is a good fit for Perl developers who need source-level stepping, conditional breakpoints, watches, and inspection of runtime data without adopting another debugger. It is less suitable when the target is compile-time behavior: executable statements in BEGIN, UNITCHECK, CHECK, and use are not stopped, although some can be traced with AutoTrace. Nor can it provide stack-frame information or debug functions not compiled by Perl, including C and C++ extension functions. It also does not currently work with Perl’s -W switch.

Pros and cons

• Pros: Included with Perl at no additional cost, with stepping, conditional breakpoints, watches, backtraces, and nested data inspection in one interactive workflow.
• Pros: Unrecognized commands run as Perl in the current package, useful for developers who want to inspect state with the language itself.
• Cons: Lexical inspection depends on PadWalker, and full command-line editing needs additional modules.
• Cons: Compile-time execution and native extension functions fall outside its debugging reach; the -W switch is also unsupported.

Alternatives

For a broader free debugger across platforms, consider GDB, whose source code is available under the GNU General Public License. LLDB is another free, open-source option spanning mobile and desktop platforms. If the work is x86 disassembly rather than Perl source debugging, IDA Pro offers a free tier with x86-32 and x86-64 disassembly and two cloud-based decompilers, alongside a paid Essential plan at 1099.00 USD. For embedded microcontrollers, Black Magic Debug is a free JTAG/SWD debugger, but requires compatible probe hardware and a suitable toolchain. pyOCD is a free open-source project; OpenOCD is free open-source software distributed through operating-system packages or source. PonyDebugger is a free Apache License 2.0 option with an iOS client and gateway server, while FlowStorm is free and open source.

Browse more options in Debuggers.

Verdict

Choose Perl Debugger if you work in Perl and want built-in, interactive control over ordinary script execution without paying for a separate debugger. Its focused workflow is useful, but compile-time code, native extensions, and dependence on optional modules for some inspection tasks are good reasons to look elsewhere when those are central to the job.