First of all, there's a few things you can do to make your life a lot more
straightforward when it comes to debugging perl programs, without using the
-debugger at all. To demonstrate, here's a simple script with a problem:
+debugger at all. To demonstrate, here's a simple script, named "hello", with
+a problem:
#!/usr/bin/perl
blank line. It looks like there's 2 variables when (because of the typo)
there's really 3:
- $var1 = 'Hello World'
- $varl = undef
- $var2 = "\n"
+ $var1 = 'Hello World';
+ $varl = undef;
+ $var2 = "\n";
To catch this kind of problem, we can force each variable to be declared
before use by pulling in the strict module, by putting 'use strict;' after the
use strict;
my $var1 = 'Hello World';
- my $varl = '';
+ my $varl = undef;
my $var2 = "$varl\n";
print $var2;
hello syntax OK
And now when we run it, we get "\n" still, but at least we know why. Just
-getting this script to compile has exposed the '$varl' (with the letter 'l)
+getting this script to compile has exposed the '$varl' (with the letter 'l')
variable, and simply changing $varl to $var1 solves the problem.
the entire help screen. Here is the summary page:
DB<1>h
-List/search source lines: Control script execution:
+
+ List/search source lines: Control script execution:
l [ln|sub] List source code T Stack trace
- or . List previous/current line s [expr] Single step [in expr]
v [line] View around line n [expr] Next, steps over subs
f filename View source in file <CR/Enter> Repeat last n or s
/pattern/ ?patt? Search forw/backw r Return from subroutine
M Show module versions c [ln|sub] Continue until position
-Debugger controls: L List break/watch/actions
+ Debugger controls: L List break/watch/actions
o [...] Set debugger options t [expr] Toggle trace [trace expr]
<[<]|{[{]|>[>] [cmd] Do pre/post-prompt b [ln|event|sub] [cnd] Set breakpoint
! [N|pat] Redo a previous command B ln|* Delete a/all breakpoints
H [-num] Display last num commands a [ln] cmd Do cmd before line
= [a val] Define/list an alias A ln|* Delete a/all actions
h [db_cmd] Get help on command w expr Add a watch expression
- h h Complete help page W expr|* Delete a/all watch expressions
+ h h Complete help page W expr|* Delete a/all watch exprs
|[|]db_cmd Send output to pager ![!] syscmd Run cmd in a subprocess
q or ^D Quit R Attempt a restart
-Data Examination: expr Execute perl code, also see: s,n,t expr
+ Data Examination: expr Execute perl code, also see: s,n,t expr
x|m expr Evals expr in list context, dumps the result or lists methods.
p expr Print expression (uses script's current package).
S [[!]pat] List subroutine names [not] matching pattern
V [Pk [Vars]] List Variables in Package. Vars can be ~pattern or !pattern.
X [Vars] Same as "V current_package [Vars]".
-For more help, type h cmd_letter, or run man perldebug for all docs.
+ y [n [Vars]] List lexicals in higher scope <n>. Vars same as V.
+ For more help, type h cmd_letter, or run man perldebug for all docs.
More confusing options than you can shake a big stick at! It's not as bad as
it looks and it's very useful to know more about all of it, and fun too!
- just about whatever you throw at it:
Let's make a quick object and x-plode it, first we'll start the debugger:
-it wants some form of input from STDIN, so we give it something non-commital,
+it wants some form of input from STDIN, so we give it something non-committal,
a zero:
> perl -de 0
17: print "$out $deg\n";
break if (1)
-Note that to delete a breakpoint you use 'd' or 'D'.
+Note that to delete a breakpoint you use 'B'.
Now we'll continue down into our subroutine, this time rather than by line
number, we'll use the subroutine name, followed by the now familiar 'v':
=head1 AUTHOR
-Richard Foley <richard@rfi.net> Copyright (c) 2000
+Richard Foley <richard.foley@rfi.net> Copyright (c) 2000
=head1 CONTRIBUTORS
https://perl5.git.perl.org / perl5.git / blobdiff