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Re^2: Perl's pearls

by dominick_t (Acolyte)
on Oct 27, 2017 at 00:41 UTC ( #1202106=note: print w/replies, xml ) Need Help??


in reply to Re: Perl's pearls
in thread Perl's pearls

Might somebody on this thread be able to walk me through certain aspects of how this code is working? I understand the general principle, but I am missing some details, and I would like to understand it precisely. I have been reading all the documentation that I can, and am figuring it out in bits and pieces, but I need to understand the behavior of this program perfectly, as I want to write a program to accomplish a similar task.

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Re^3: Perl's pearls
by roboticus (Chancellor) on Oct 27, 2017 at 04:16 UTC

    dominick_t:

    I'd suggest running it under the debugger (perl -d script.pl) and examine the interesting bits and/or the bits you don't understand. The debugger isn't terribly difficult to use, and it's the easiest way to suss out the details you don't understand yet.

    $ perl -d pm_135391.pl Loading DB routines from perl5db.pl version 1.49_001 Editor support available. Enter h or 'h h' for help, or 'man perldebug' for more help. main::(pm_135391.pl:1): while (<DATA>) { DB<1> n main::(pm_135391.pl:2): chomp; DB<1> p "<$_>" <Abby >

    So here, we started the program under the debugger, executed the first statement (loading $_ from <DATA>), then displayed the value using the p command. (I used "<$_>" to put delimiters around the value, so you can see that it has end-of-line characters in it.

    DB<2> n main::(pm_135391.pl:3): my $key = lc $_; DB<2> n main::(pm_135391.pl:4): next if $seen{$key}++; DB<2> n main::(pm_135391.pl:5): my $signature = join "", sort split //, $key +; DB<2> x %seen 0 "abby \cM" 1 1

    Here, we executed the next three lines to chomp the value, make the $key value, and add $key to the %seen hash. Then I used the x command to display the %seen hash, so you can see what's in it.

    DB<3> n main::(pm_135391.pl:6): push @{$words{$signature}}, $_; DB<3> x $signature 0 "\cM abby" DB<4> h 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 subr +outine M Show module versions c [ln|sub] Continue until p +osition Debugger controls: L List break/watch +/actions o [...] Set debugger options t [n] [expr] Toggle trace [m +ax depth] ][trace expr] <[<]|{[{]|>[>] [cmd] Do pre/post-prompt b [ln|event|sub] [cnd] Set b +reakpoint ! [N|pat] Redo a previous command B ln|* Delete a/all bre +akpoints H [-num] Display last num commands a [ln] cmd Do cmd before li +ne = [a val] Define/list an alias A ln|* Delete a/all act +ions h [db_cmd] Get help on command w expr Add a watch expr +ession h h Complete help page W expr|* Delete a/all wat +ch exprs |[|]db_cmd Send output to pager ![!] syscmd Run cmd in a sub +process q or ^D Quit R Attempt a restar +t 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]". i class inherita +nce tree. y [n [Vars]] List lexicals in higher scope <n>. Vars same as V. e Display thread id E Display all thread ids. For more help, type h cmd_letter, or run man perldebug for all docs.

    Then, I decided I showed you enough ;^) and had it print the help page. Have fun with it!

    ...roboticus

    When your only tool is a hammer, all problems look like your thumb.

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