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
+ - 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
- 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
+ /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
+ 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 exprs
- |[|]db_cmd Send output to pager ![!] syscmd Run cmd in a subprocess
+ = [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
+ 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
- x|m expr Evals expr in list context, dumps the result or lists methods.
+ 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.
+ V [Pk [Vars]] List Variables in Package. Vars can be ~pattern or
+ !pattern.
X [Vars] Same as "V current_package [Vars]".
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.
it wants some form of input from STDIN, so we give it something non-committal,
a zero:
- > perl -de 0
- Default die handler restored.
+ > perl -de 0
+ Default die handler restored.
- Loading DB routines from perl5db.pl version 1.07
- Editor support available.
+ Loading DB routines from perl5db.pl version 1.07
+ Editor support available.
- Enter h or `h h' for help, or `man perldebug' for more help.
+ Enter h or `h h' for help, or `man perldebug' for more help.
- main::(-e:1): 0
+ main::(-e:1): 0
Now build an on-the-fly object over a couple of lines (note the backslash):
- DB<1> $obj = bless({'unique_id'=>'123', 'attr'=> \
- cont: {'col' => 'black', 'things' => [qw(this that etc)]}}, 'MY_class')
+ DB<1> $obj = bless({'unique_id'=>'123', 'attr'=> \
+ cont: {'col' => 'black', 'things' => [qw(this that etc)]}}, 'MY_class')
And let's have a look at it:
DB<2> x $obj
- 0 MY_class=HASH(0x828ad98)
+ 0 MY_class=HASH(0x828ad98)
'attr' => HASH(0x828ad68)
'col' => 'black'
'things' => ARRAY(0x828abb8)
Useful, huh? You can eval nearly anything in there, and experiment with bits
of code or regexes until the cows come home:
- DB<3> @data = qw(this that the other atheism leather theory scythe)
+ DB<3> @data = qw(this that the other atheism leather theory scythe)
- DB<4> p 'saw -> '.($cnt += map { print "\t:\t$_\n" } grep(/the/, sort @data))
- atheism
- leather
- other
- scythe
- the
- theory
- saw -> 6
+ DB<4> p 'saw -> '.($cnt += map { print "\t:\t$_\n" } grep(/the/, sort @data))
+ atheism
+ leather
+ other
+ scythe
+ the
+ theory
+ saw -> 6
If you want to see the command History, type an 'B<H>':
- DB<5> H
- 4: p 'saw -> '.($cnt += map { print "\t:\t$_\n" } grep(/the/, sort @data))
- 3: @data = qw(this that the other atheism leather theory scythe)
- 2: x $obj
- 1: $obj = bless({'unique_id'=>'123', 'attr'=>
- {'col' => 'black', 'things' => [qw(this that etc)]}}, 'MY_class')
- DB<5>
+ DB<5> H
+ 4: p 'saw -> '.($cnt += map { print "\t:\t$_\n" } grep(/the/, sort @data))
+ 3: @data = qw(this that the other atheism leather theory scythe)
+ 2: x $obj
+ 1: $obj = bless({'unique_id'=>'123', 'attr'=>
+ {'col' => 'black', 'things' => [qw(this that etc)]}}, 'MY_class')
+ DB<5>
And if you want to repeat any previous command, use the exclamation: 'B<!>':
- DB<5> !4
- p 'saw -> '.($cnt += map { print "$_\n" } grep(/the/, sort @data))
- atheism
- leather
- other
- scythe
- the
- theory
- saw -> 12
+ DB<5> !4
+ p 'saw -> '.($cnt += map { print "$_\n" } grep(/the/, sort @data))
+ atheism
+ leather
+ other
+ scythe
+ the
+ theory
+ saw -> 12
For more on references see L<perlref> and L<perlreftut>
Here's a simple program which converts between Celsius and Fahrenheit, it too
has a problem:
- #!/usr/bin/perl -w
- use strict;
-
- my $arg = $ARGV[0] || '-c20';
-
- if ($arg =~ /^\-(c|f)((\-|\+)*\d+(\.\d+)*)$/) {
- my ($deg, $num) = ($1, $2);
- my ($in, $out) = ($num, $num);
- if ($deg eq 'c') {
- $deg = 'f';
- $out = &c2f($num);
- } else {
- $deg = 'c';
- $out = &f2c($num);
- }
- $out = sprintf('%0.2f', $out);
- $out =~ s/^((\-|\+)*\d+)\.0+$/$1/;
- print "$out $deg\n";
- } else {
- print "Usage: $0 -[c|f] num\n";
- }
- exit;
+ #!/usr/bin/perl -w
+ use strict;
- sub f2c {
- my $f = shift;
- my $c = 5 * $f - 32 / 9;
- return $c;
- }
+ my $arg = $ARGV[0] || '-c20';
- sub c2f {
- my $c = shift;
- my $f = 9 * $c / 5 + 32;
- return $f;
+ if ($arg =~ /^\-(c|f)((\-|\+)*\d+(\.\d+)*)$/) {
+ my ($deg, $num) = ($1, $2);
+ my ($in, $out) = ($num, $num);
+ if ($deg eq 'c') {
+ $deg = 'f';
+ $out = &c2f($num);
+ } else {
+ $deg = 'c';
+ $out = &f2c($num);
}
+ $out = sprintf('%0.2f', $out);
+ $out =~ s/^((\-|\+)*\d+)\.0+$/$1/;
+ print "$out $deg\n";
+ } else {
+ print "Usage: $0 -[c|f] num\n";
+ }
+ exit;
+
+ sub f2c {
+ my $f = shift;
+ my $c = 5 * $f - 32 / 9;
+ return $c;
+ }
+
+ sub c2f {
+ my $c = shift;
+ my $f = 9 * $c / 5 + 32;
+ return $f;
+ }
For some reason, the Fahrenheit to Celsius conversion fails to return the
expected output. This is what it does:
- > temp -c0.72
- 33.30 f
+ > temp -c0.72
+ 33.30 f
- > temp -f33.3
- 162.94 c
+ > temp -f33.3
+ 162.94 c
Not very consistent! We'll set a breakpoint in the code manually and run it
under the debugger to see what's going on. A breakpoint is a flag, to which
Ever wanted to know what a regex looked like? You'll need perl compiled with
the DEBUGGING flag for this one:
- > perl -Dr -e '/^pe(a)*rl$/i'
- Compiling REx `^pe(a)*rl$'
- size 17 first at 2
- rarest char
- at 0
- 1: BOL(2)
- 4: CURLYN[1] {0,32767}(14)
- 6: NOTHING(8)
- 12: WHILEM(0)
- 13: NOTHING(14)
- 14: EXACTF <rl>(16)
- 16: EOL(17)
- 17: END(0)
- floating `'$ at 4..2147483647 (checking floating) stclass `EXACTF <pe>'
-anchored(BOL) minlen 4
- Omitting $` $& $' support.
-
- EXECUTING...
-
- Freeing REx: `^pe(a)*rl$'
+ > perl -Dr -e '/^pe(a)*rl$/i'
+ Compiling REx `^pe(a)*rl$'
+ size 17 first at 2
+ rarest char
+ at 0
+ 1: BOL(2)
+ 2: EXACTF <pe>(4)
+ 4: CURLYN[1] {0,32767}(14)
+ 6: NOTHING(8)
+ 8: EXACTF <a>(0)
+ 12: WHILEM(0)
+ 13: NOTHING(14)
+ 14: EXACTF <rl>(16)
+ 16: EOL(17)
+ 17: END(0)
+ floating `'$ at 4..2147483647 (checking floating) stclass
+ `EXACTF <pe>' anchored(BOL) minlen 4
+ Omitting $` $& $' support.
+
+ EXECUTING...
+
+ Freeing REx: `^pe(a)*rl$'
Did you really want to know? :-)
For more gory details on getting regular expressions to work, have a look at
Wrapping all die calls in a handler routine can be useful to see how, and from
where, they're being called, L<perlvar> has more information:
- BEGIN { $SIG{__DIE__} = sub { require Carp; Carp::confess(@_) } }
+ BEGIN { $SIG{__DIE__} = sub { require Carp; Carp::confess(@_) } }
Various useful techniques for the redirection of STDOUT and STDERR filehandles
are explained in L<perlopentut> and L<perlfaq8>.
https://perl5.git.perl.org / perl5.git / blobdiff