Programming Perl, 4th Edition

Actions and Command Execution

From inside the debugger, you can specify actions to be taken at particular times. You can also launch external programs.

a

a COMMAND

a LINE

a LINE COMMAND

This command sets an action to take before LINE executes, or the current line if LINE is omitted. For example, this prints out $foo every time line 53 is reached:

a 53 print "DB FOUND $foo\n"

If no COMMAND is specified, the action on the specified LINE is deleted. With neither LINE nor COMMAND, the action on the current line is deleted.

A

The A debugger command deletes all actions.

<

< ?

< EXPR

<< EXPR

The < EXPR form specifies a Perl expression to be evaluated before every debugger prompt. You can add another expression with the << EXPR form, list them with < ?, and delete them all with a plain <.

>

> ?

> EXPR

>> EXPR

The > commands behave just like their < cousins but are executed after the debugger prompt instead of before.

{

{ ?

{ COMMAND

{{ COMMAND

The { debugger commands behave just like < but specify a debugger command to be executed before the debugger prompt instead of a Perl expression. A warning is issued if you appear to have accidentally entered a block of code instead. If that’s what you really mean to do, write it with ;{ ... } or even do { ... }.

!

! NUMBER

! –NUMBER

!PATTERN

A lone ! repeats the previous command. The NUMBER specifies which command from the history to execute; for instance, ! 3 executes the third command typed into the debugger. If a minus sign precedes the NUMBER, the commands are counted backward: ...