Programming Perl, 4th Edition

Display

Perl’s debugger has several commands for examining data structures while your program is stopped at a breakpoint.

p

p EXPR

This command is the same as print DB::OUT EXPR in the current package. In particular, since this is just Perl’s own print function, nested data structures and objects are not shown—use the x command for that. The DB::OUT handle prints to your terminal (or perhaps an editor window) no matter where standard output may have been redirected.

x

x EXPR

The x command evaluates its expression in list context and displays the result, pretty printed. That is, nested data structures are printed out recursively and with unviewable characters suitably encoded.

V

V PKG

V PKG VARS

This command displays all (or when you specify VARS, some) variables in the specified PKG (defaulting to the main package) using a pretty printer. Hashes show their keys and values, control characters are rendered legibly, nested data structures print out in a legible fashion, and so on. This is similar to calling the x command on each applicable variable, except that x works with lexical variables, too. Also, here you type the identifiers without a type specifier such as $ or @, like this:

V Pet::Camel SPOT FIDO

In place of a variable name in VARS, you can use ~PATTERN or !PATTERN to print existing variables whose names either match or don’t match the specified pattern.

X

X VARS

This command is the same as V CURRENTPACKAGE, where CURRENTPACKAGE is the package into which the current line was compiled.