{ "content": [ { "type": "text", "text": "# PERLFAQ3(1) (man)\n\n**Summary:** perlfaq3 - Programming Tools\n\n## Section Outline\n\n- **NAME** (2 lines)\n- **VERSION** (2 lines)\n- **DESCRIPTION** (3 lines) — 29 subsections\n - How do I do (anything)? (47 lines)\n - How can I use Perl interactively? (12 lines)\n - How do I find which modules are installed on my system? (62 lines)\n - How do I debug my Perl programs? (34 lines)\n - How do I profile my Perl programs? (32 lines)\n - How do I cross-reference my Perl programs? (4 lines)\n - Is there a pretty-printer (formatter) for Perl? (19 lines)\n - Is there an IDE or Windows Perl Editor? (149 lines)\n - Where can I get Perl macros for vi? (6 lines)\n - Where can I get perl-mode or cperl-mode for emacs? (9 lines)\n - How can I use curses with Perl? (5 lines)\n - How can I write a GUI (X, Tk, Gtk, etc.) in Perl? (45 lines)\n - How can I make my Perl program run faster? (23 lines)\n - How can I make my Perl program take less memory? (99 lines)\n - Is it safe to return a reference to local or lexical data? (15 lines)\n - How can I free an array or hash so my program shrinks? (18 lines)\n - How can I make my CGI script more efficient? (32 lines)\n - How can I hide the source for my Perl program? (33 lines)\n - How can I compile my Perl program into byte code or C? (21 lines)\n - How can I get \"#!perl\" to work on [MS-DOS,NT,...]? (25 lines)\n - Can I write useful Perl programs on the command line? (24 lines)\n - Why don't Perl one-liners work on my DOS/Mac/VMS system? (40 lines)\n - Where can I learn about CGI or Web programming in Perl? (12 lines)\n - Where can I learn about object-oriented Perl programming? (6 lines)\n - Where can I learn about linking C with Perl? (9 lines)\n - I've read perlembed, perlguts, etc., but I can't embed perl (1 lines)\n - wrong? (5 lines)\n - When I tried to run my script, I got this message. What does (15 lines)\n - What's MakeMaker? (6 lines)\n- **AUTHOR AND COPYRIGHT** (14 lines)\n\n## Full Content\n\n### NAME\n\nperlfaq3 - Programming Tools\n\n### VERSION\n\nversion 5.20210411\n\n### DESCRIPTION\n\nThis section of the FAQ answers questions related to programmer tools and programming\nsupport.\n\n#### How do I do (anything)?\n\nHave you looked at CPAN (see perlfaq2)? The chances are that someone has already written a\nmodule that can solve your problem. Have you read the appropriate manpages? Here's a brief\nindex:\n\nBasics\nperldata - Perl data types\nperlvar - Perl pre-defined variables\nperlsyn - Perl syntax\nperlop - Perl operators and precedence\nperlsub - Perl subroutines\nExecution\nperlrun - how to execute the Perl interpreter\nperldebug - Perl debugging\nFunctions\nperlfunc - Perl builtin functions\nObjects\nperlref - Perl references and nested data structures\nperlmod - Perl modules (packages and symbol tables)\nperlobj - Perl objects\nperltie - how to hide an object class in a simple variable\nData Structures\nperlref - Perl references and nested data structures\nperllol - Manipulating arrays of arrays in Perl\nperldsc - Perl Data Structures Cookbook\nModules\nperlmod - Perl modules (packages and symbol tables)\nperlmodlib - constructing new Perl modules and finding existing ones\nRegexes\nperlre - Perl regular expressions\nperlfunc - Perl builtin functions>\nperlop - Perl operators and precedence\nperllocale - Perl locale handling (internationalization and localization)\nMoving to perl5\nperltrap - Perl traps for the unwary\nperl\nLinking with C\nperlxstut - Tutorial for writing XSUBs\nperlxs - XS language reference manual\nperlcall - Perl calling conventions from C\nperlguts - Introduction to the Perl API\nperlembed - how to embed perl in your C program\nVarious\n (not a man-page but still useful, a\ncollection of various essays on Perl techniques)\n\nA crude table of contents for the Perl manpage set is found in perltoc.\n\n#### How can I use Perl interactively?\n\nThe typical approach uses the Perl debugger, described in the perldebug(1) manpage, on an\n\"empty\" program, like this:\n\nperl -de 42\n\nNow just type in any legal Perl code, and it will be immediately evaluated. You can also\nexamine the symbol table, get stack backtraces, check variable values, set breakpoints, and\nother operations typically found in symbolic debuggers.\n\nYou can also use Devel::REPL which is an interactive shell for Perl, commonly known as a REPL\n- Read, Evaluate, Print, Loop. It provides various handy features.\n\n#### How do I find which modules are installed on my system?\n\nFrom the command line, you can use the \"cpan\" command's \"-l\" switch:\n\n$ cpan -l\n\nYou can also use \"cpan\"'s \"-a\" switch to create an autobundle file that \"CPAN.pm\" understands\nand can use to re-install every module:\n\n$ cpan -a\n\nInside a Perl program, you can use the ExtUtils::Installed module to show all installed\ndistributions, although it can take awhile to do its magic. The standard library which comes\nwith Perl just shows up as \"Perl\" (although you can get those with Module::CoreList).\n\nuse ExtUtils::Installed;\n\nmy $inst = ExtUtils::Installed->new();\nmy @modules = $inst->modules();\n\nIf you want a list of all of the Perl module filenames, you can use File::Find::Rule:\n\nuse File::Find::Rule;\n\nmy @files = File::Find::Rule->\nextras({follow => 1})->\nfile()->\nname( '*.pm' )->\nin( @INC )\n;\n\nIf you do not have that module, you can do the same thing with File::Find which is part of\nthe standard library:\n\nuse File::Find;\nmy @files;\n\nfind(\n{\nwanted => sub {\npush @files, $File::Find::fullname\nif -f $File::Find::fullname && /\\.pm$/\n},\nfollow => 1,\nfollowskip => 2,\n},\n@INC\n);\n\nprint join \"\\n\", @files;\n\nIf you simply need to check quickly to see if a module is available, you can check for its\ndocumentation. If you can read the documentation the module is most likely installed. If you\ncannot read the documentation, the module might not have any (in rare cases):\n\n$ perldoc Module::Name\n\nYou can also try to include the module in a one-liner to see if perl finds it:\n\n$ perl -MModule::Name -e1\n\n(If you don't receive a \"Can't locate ... in @INC\" error message, then Perl found the module\nname you asked for.)\n\n#### How do I debug my Perl programs?\n\n(contributed by brian d foy)\n\nBefore you do anything else, you can help yourself by ensuring that you let Perl tell you\nabout problem areas in your code. By turning on warnings and strictures, you can head off\nmany problems before they get too big. You can find out more about these in strict and\nwarnings.\n\n#!/usr/bin/perl\nuse strict;\nuse warnings;\n\nBeyond that, the simplest debugger is the \"print\" function. Use it to look at values as you\nrun your program:\n\nprint STDERR \"The value is [$value]\\n\";\n\nThe Data::Dumper module can pretty-print Perl data structures:\n\nuse Data::Dumper qw( Dumper );\nprint STDERR \"The hash is \" . Dumper( \\%hash ) . \"\\n\";\n\nPerl comes with an interactive debugger, which you can start with the \"-d\" switch. It's fully\nexplained in perldebug.\n\nIf you'd like a graphical user interface and you have Tk, you can use \"ptkdb\". It's on CPAN\nand available for free.\n\nIf you need something much more sophisticated and controllable, Leon Brocard's Devel::ebug\n(which you can call with the \"-D\" switch as \"-Debug\") gives you the programmatic hooks into\neverything you need to write your own (without too much pain and suffering).\n\nYou can also use a commercial debugger such as Affrus (Mac OS X), Komodo from Activestate\n(Windows and Mac OS X), or EPIC (most platforms).\n\n#### How do I profile my Perl programs?\n\n(contributed by brian d foy, updated Fri Jul 25 12:22:26 PDT 2008)\n\nThe \"Devel\" namespace has several modules which you can use to profile your Perl programs.\n\nThe Devel::NYTProf (New York Times Profiler) does both statement and subroutine profiling.\nIt's available from CPAN and you also invoke it with the \"-d\" switch:\n\nperl -d:NYTProf someperl.pl\n\nIt creates a database of the profile information that you can turn into reports. The\n\"nytprofhtml\" command turns the data into an HTML report similar to the Devel::Cover report:\n\nnytprofhtml\n\nYou might also be interested in using the Benchmark to measure and compare code snippets.\n\nYou can read more about profiling in Programming Perl, chapter 20, or Mastering Perl, chapter\n5.\n\nperldebguts documents creating a custom debugger if you need to create a special sort of\nprofiler. brian d foy describes the process in The Perl Journal, \"Creating a Perl Debugger\",\n , and \"Profiling in Perl\" .\n\nPerl.com has two interesting articles on profiling: \"Profiling Perl\", by Simon Cozens,\n and \"Debugging and Profiling modperl\nApplications\", by Frank Wiles, .\n\nRandal L. Schwartz writes about profiling in \"Speeding up Your Perl Programs\" for Unix\nReview, , and \"Profiling in Template\nToolkit via Overriding\" for Linux Magazine,\n .\n\n#### How do I cross-reference my Perl programs?\n\nThe B::Xref module can be used to generate cross-reference reports for Perl programs.\n\nperl -MO=Xref[,OPTIONS] scriptname.plx\n\n#### Is there a pretty-printer (formatter) for Perl?\n\nPerl::Tidy comes with a perl script perltidy which indents and reformats Perl scripts to make\nthem easier to read by trying to follow the rules of the perlstyle. If you write Perl, or\nspend much time reading Perl, you will probably find it useful.\n\nOf course, if you simply follow the guidelines in perlstyle, you shouldn't need to reformat.\nThe habit of formatting your code as you write it will help prevent bugs. Your editor can and\nshould help you with this. The perl-mode or newer cperl-mode for emacs can provide remarkable\namounts of help with most (but not all) code, and even less programmable editors can provide\nsignificant assistance. Tom Christiansen and many other VI users swear by the following\nsettings in vi and its clones:\n\nset ai sw=4\nmap! ^O {^M}^[O^T\n\nPut that in your .exrc file (replacing the caret characters with control characters) and away\nyou go. In insert mode, ^T is for indenting, ^D is for undenting, and ^O is for\nblockdenting--as it were. A more complete example, with comments, can be found at\n\n\n#### Is there an IDE or Windows Perl Editor?\n\nPerl programs are just plain text, so any editor will do.\n\nIf you're on Unix, you already have an IDE--Unix itself. The Unix philosophy is the\nphilosophy of several small tools that each do one thing and do it well. It's like a\ncarpenter's toolbox.\n\nIf you want an IDE, check the following (in alphabetical order, not order of preference):\n\nEclipse\n\n\nThe Eclipse Perl Integration Project integrates Perl editing/debugging with Eclipse.\n\nEnginsite\n\n\nPerl Editor by EngInSite is a complete integrated development environment (IDE) for\ncreating, testing, and debugging Perl scripts; the tool runs on Windows 9x/NT/2000/XP\nor later.\n\nIntelliJ IDEA\n\n\nCamelcade plugin provides Perl5 support in IntelliJ IDEA and other JetBrains IDEs.\n\nKephra\n\n\nGUI editor written in Perl using wxWidgets and Scintilla with lots of smaller features.\nAims for a UI based on Perl principles like TIMTOWTDI and \"easy things should be easy,\nhard things should be possible\".\n\nKomodo\n\n\nActiveState's cross-platform (as of October 2004, that's Windows, Linux, and Solaris),\nmulti-language IDE has Perl support, including a regular expression debugger and remote\ndebugging.\n\nNotepad++\n\n\nOpen Perl IDE\n\n\nOpen Perl IDE is an integrated development environment for writing and debugging Perl\nscripts with ActiveState's ActivePerl distribution under Windows 95/98/NT/2000.\n\nOptiPerl\n\n\nOptiPerl is a Windows IDE with simulated CGI environment, including debugger and syntax-\nhighlighting editor.\n\nPadre\n\n\nPadre is cross-platform IDE for Perl written in Perl using wxWidgets to provide a native\nlook and feel. It's open source under the Artistic License. It is one of the newer Perl\nIDEs.\n\nPerlBuilder\n\n\nPerlBuilder is an integrated development environment for Windows that supports Perl\ndevelopment.\n\nvisiPerl+\n\n\nFrom Help Consulting, for Windows.\n\nVisual Perl\n\n\nVisual Perl is a Visual Studio.NET plug-in from ActiveState.\n\nZeus\n\n\nZeus for Windows is another Win32 multi-language editor/IDE that comes with support for\nPerl.\n\nFor editors: if you're on Unix you probably have vi or a vi clone already, and possibly an\nemacs too, so you may not need to download anything. In any emacs the cperl-mode (M-x cperl-\nmode) gives you perhaps the best available Perl editing mode in any editor.\n\nIf you are using Windows, you can use any editor that lets you work with plain text, such as\nNotePad or WordPad. Word processors, such as Microsoft Word or WordPerfect, typically do not\nwork since they insert all sorts of behind-the-scenes information, although some allow you to\nsave files as \"Text Only\". You can also download text editors designed specifically for\nprogramming, such as Textpad ( ) and UltraEdit (\n ), among others.\n\nIf you are using MacOS, the same concerns apply. MacPerl (for Classic environments) comes\nwith a simple editor. Popular external editors are BBEdit (\n ) or Alpha (\n ). MacOS X users can use Unix editors as well.\n\nGNU Emacs\n\n\nMicroEMACS\n\n\nXEmacs\n\n\nJed \n\nor a vi clone such as\n\nVim \n\nVile\n\n\nThe following are Win32 multilanguage editor/IDEs that support Perl:\n\nMultiEdit\n\n\nSlickEdit\n\n\nConTEXT\n\n\nThere is also a toyedit Text widget based editor written in Perl that is distributed with the\nTk module on CPAN. The ptkdb ( ) is a Perl/Tk-based debugger\nthat acts as a development environment of sorts. Perl Composer (\n ) is an IDE for Perl/Tk GUI creation.\n\nIn addition to an editor/IDE you might be interested in a more powerful shell environment for\nWin32. Your options include\n\nbash\nfrom the Cygwin package ( )\n\nzsh \n\nCygwin is covered by the GNU General Public License (but that shouldn't matter for Perl use).\nCygwin contains (in addition to the shell) a comprehensive set of standard Unix toolkit\nutilities.\n\nBBEdit and TextWrangler\nare text editors for OS X that have a Perl sensitivity mode ( \n).\n\n#### Where can I get Perl macros for vi?\n\nFor a complete version of Tom Christiansen's vi configuration file, see\n , the standard benchmark file\nfor vi emulators. The file runs best with nvi, the current version of vi out of Berkeley,\nwhich incidentally can be built with an embedded Perl interpreter--see\n .\n\n#### Where can I get perl-mode or cperl-mode for emacs?\n\nSince Emacs version 19 patchlevel 22 or so, there have been both a perl-mode.el and support\nfor the Perl debugger built in. These should come with the standard Emacs 19 distribution.\n\nNote that the perl-mode of emacs will have fits with \"main'foo\" (single quote), and mess up\nthe indentation and highlighting. You are probably using \"main::foo\" in new Perl code anyway,\nso this shouldn't be an issue.\n\nFor CPerlMode, see \n\n#### How can I use curses with Perl?\n\nThe Curses module from CPAN provides a dynamically loadable object module interface to a\ncurses library. A small demo can be found at the directory\n ; this program repeats a command\nand updates the screen as needed, rendering rep ps axu similar to top.\n\n#### How can I write a GUI (X, Tk, Gtk, etc.) in Perl?\n\n(contributed by Ben Morrow)\n\nThere are a number of modules which let you write GUIs in Perl. Most GUI toolkits have a perl\ninterface: an incomplete list follows.\n\nTk This works under Unix and Windows, and the current version doesn't look half as bad under\nWindows as it used to. Some of the gui elements still don't 'feel' quite right, though.\nThe interface is very natural and 'perlish', making it easy to use in small scripts that\njust need a simple gui. It hasn't been updated in a while.\n\nWx This is a Perl binding for the cross-platform wxWidgets toolkit (\n ). It works under Unix, Win32 and Mac OS X, using native\nwidgets (Gtk under Unix). The interface follows the C++ interface closely, but the\ndocumentation is a little sparse for someone who doesn't know the library, mostly just\nreferring you to the C++ documentation.\n\nGtk and Gtk2\nThese are Perl bindings for the Gtk toolkit ( ). The interface\nchanged significantly between versions 1 and 2 so they have separate Perl modules. It\nruns under Unix, Win32 and Mac OS X (currently it requires an X server on Mac OS, but a\n'native' port is underway), and the widgets look the same on every platform: i.e., they\ndon't match the native widgets. As with Wx, the Perl bindings follow the C API closely,\nand the documentation requires you to read the C documentation to understand it.\n\nWin32::GUI\nThis provides access to most of the Win32 GUI widgets from Perl. Obviously, it only runs\nunder Win32, and uses native widgets. The Perl interface doesn't really follow the C\ninterface: it's been made more Perlish, and the documentation is pretty good. More\nadvanced stuff may require familiarity with the C Win32 APIs, or reference to MSDN.\n\nCamelBones\nCamelBones ( ) is a Perl interface to Mac OS X's\nCocoa GUI toolkit, and as such can be used to produce native GUIs on Mac OS X. It's not\non CPAN, as it requires frameworks that CPAN.pm doesn't know how to install, but\ninstallation is via the standard OSX package installer. The Perl API is, again, very\nclose to the ObjC API it's wrapping, and the documentation just tells you how to\ntranslate from one to the other.\n\nQt There is a Perl interface to TrollTech's Qt toolkit, but it does not appear to be\nmaintained.\n\nAthena\nSx is an interface to the Athena widget set which comes with X, but again it appears not\nto be much used nowadays.\n\n#### How can I make my Perl program run faster?\n\nThe best way to do this is to come up with a better algorithm. This can often make a dramatic\ndifference. Jon Bentley's book Programming Pearls (that's not a misspelling!) has some good\ntips on optimization, too. Advice on benchmarking boils down to: benchmark and profile to\nmake sure you're optimizing the right part, look for better algorithms instead of microtuning\nyour code, and when all else fails consider just buying faster hardware. You will probably\nwant to read the answer to the earlier question \"How do I profile my Perl programs?\" if you\nhaven't done so already.\n\nA different approach is to autoload seldom-used Perl code. See the AutoSplit and AutoLoader\nmodules in the standard distribution for that. Or you could locate the bottleneck and think\nabout writing just that part in C, the way we used to take bottlenecks in C code and write\nthem in assembler. Similar to rewriting in C, modules that have critical sections can be\nwritten in C (for instance, the PDL module from CPAN).\n\nIf you're currently linking your perl executable to a shared libc.so, you can often gain a\n10-25% performance benefit by rebuilding it to link with a static libc.a instead. This will\nmake a bigger perl executable, but your Perl programs (and programmers) may thank you for it.\nSee the INSTALL file in the source distribution for more information.\n\nThe undump program was an ancient attempt to speed up Perl program by storing the already-\ncompiled form to disk. This is no longer a viable option, as it only worked on a few\narchitectures, and wasn't a good solution anyway.\n\n#### How can I make my Perl program take less memory?\n\nWhen it comes to time-space tradeoffs, Perl nearly always prefers to throw memory at a\nproblem. Scalars in Perl use more memory than strings in C, arrays take more than that, and\nhashes use even more. While there's still a lot to be done, recent releases have been\naddressing these issues. For example, as of 5.004, duplicate hash keys are shared amongst all\nhashes using them, so require no reallocation.\n\nIn some cases, using substr() or vec() to simulate arrays can be highly beneficial. For\nexample, an array of a thousand booleans will take at least 20,000 bytes of space, but it can\nbe turned into one 125-byte bit vector--a considerable memory savings. The standard\nTie::SubstrHash module can also help for certain types of data structure. If you're working\nwith specialist data structures (matrices, for instance) modules that implement these in C\nmay use less memory than equivalent Perl modules.\n\nAnother thing to try is learning whether your Perl was compiled with the system malloc or\nwith Perl's builtin malloc. Whichever one it is, try using the other one and see whether this\nmakes a difference. Information about malloc is in the INSTALL file in the source\ndistribution. You can find out whether you are using perl's malloc by typing \"perl\n-V:usemymalloc\".\n\nOf course, the best way to save memory is to not do anything to waste it in the first place.\nGood programming practices can go a long way toward this:\n\nDon't slurp!\nDon't read an entire file into memory if you can process it line by line. Or more\nconcretely, use a loop like this:\n\n#\n# Good Idea\n#\nwhile (my $line = <$filehandle>) {\n# ...\n}\n\ninstead of this:\n\n#\n# Bad Idea\n#\nmy @data = <$filehandle>;\nforeach (@data) {\n# ...\n}\n\nWhen the files you're processing are small, it doesn't much matter which way you do it,\nbut it makes a huge difference when they start getting larger.\n\nUse map and grep selectively\nRemember that both map and grep expect a LIST argument, so doing this:\n\n@wanted = grep {/pattern/} <$filehandle>;\n\nwill cause the entire file to be slurped. For large files, it's better to loop:\n\nwhile (<$filehandle>) {\npush(@wanted, $) if /pattern/;\n}\n\nAvoid unnecessary quotes and stringification\nDon't quote large strings unless absolutely necessary:\n\nmy $copy = \"$largestring\";\n\nmakes 2 copies of $largestring (one for $copy and another for the quotes), whereas\n\nmy $copy = $largestring;\n\nonly makes one copy.\n\nDitto for stringifying large arrays:\n\n{\nlocal $, = \"\\n\";\nprint @bigarray;\n}\n\nis much more memory-efficient than either\n\nprint join \"\\n\", @bigarray;\n\nor\n\n{\nlocal $\" = \"\\n\";\nprint \"@bigarray\";\n}\n\nPass by reference\nPass arrays and hashes by reference, not by value. For one thing, it's the only way to\npass multiple lists or hashes (or both) in a single call/return. It also avoids creating\na copy of all the contents. This requires some judgement, however, because any changes\nwill be propagated back to the original data. If you really want to mangle (er, modify) a\ncopy, you'll have to sacrifice the memory needed to make one.\n\nTie large variables to disk\nFor \"big\" data stores (i.e. ones that exceed available memory) consider using one of the\nDB modules to store it on disk instead of in RAM. This will incur a penalty in access\ntime, but that's probably better than causing your hard disk to thrash due to massive\nswapping.\n\n#### Is it safe to return a reference to local or lexical data?\n\nYes. Perl's garbage collection system takes care of this so everything works out right.\n\nsub makeone {\nmy @a = ( 1 .. 10 );\nreturn \\@a;\n}\n\nfor ( 1 .. 10 ) {\npush @many, makeone();\n}\n\nprint $many[4][5], \"\\n\";\n\nprint \"@many\\n\";\n\n#### How can I free an array or hash so my program shrinks?\n\n(contributed by Michael Carman)\n\nYou usually can't. Memory allocated to lexicals (i.e. my() variables) cannot be reclaimed or\nreused even if they go out of scope. It is reserved in case the variables come back into\nscope. Memory allocated to global variables can be reused (within your program) by using\nundef() and/or delete().\n\nOn most operating systems, memory allocated to a program can never be returned to the system.\nThat's why long-running programs sometimes re- exec themselves. Some operating systems\n(notably, systems that use mmap(2) for allocating large chunks of memory) can reclaim memory\nthat is no longer used, but on such systems, perl must be configured and compiled to use the\nOS's malloc, not perl's.\n\nIn general, memory allocation and de-allocation isn't something you can or should be worrying\nabout much in Perl.\n\nSee also \"How can I make my Perl program take less memory?\"\n\n#### How can I make my CGI script more efficient?\n\nBeyond the normal measures described to make general Perl programs faster or smaller, a CGI\nprogram has additional issues. It may be run several times per second. Given that each time\nit runs it will need to be re-compiled and will often allocate a megabyte or more of system\nmemory, this can be a killer. Compiling into C isn't going to help you because the process\nstart-up overhead is where the bottleneck is.\n\nThere are three popular ways to avoid this overhead. One solution involves running the Apache\nHTTP server (available from ) with either of the modperl or\nmodfastcgi plugin modules.\n\nWith modperl and the Apache::Registry module (distributed with modperl), httpd will run\nwith an embedded Perl interpreter which pre-compiles your script and then executes it within\nthe same address space without forking. The Apache extension also gives Perl access to the\ninternal server API, so modules written in Perl can do just about anything a module written\nin C can. For more on modperl, see \n\nWith the FCGI module (from CPAN) and the modfastcgi module (available from\n ) each of your Perl programs becomes a permanent CGI daemon\nprocess.\n\nFinally, Plack is a Perl module and toolkit that contains PSGI middleware, helpers and\nadapters to web servers, allowing you to easily deploy scripts which can continue running,\nand provides flexibility with regards to which web server you use. It can allow existing CGI\nscripts to enjoy this flexibility and performance with minimal changes, or can be used along\nwith modern Perl web frameworks to make writing and deploying web services with Perl a\nbreeze.\n\nThese solutions can have far-reaching effects on your system and on the way you write your\nCGI programs, so investigate them with care.\n\nSee also .\n\n#### How can I hide the source for my Perl program?\n\nDelete it. :-) Seriously, there are a number of (mostly unsatisfactory) solutions with\nvarying levels of \"security\".\n\nFirst of all, however, you can't take away read permission, because the source code has to be\nreadable in order to be compiled and interpreted. (That doesn't mean that a CGI script's\nsource is readable by people on the web, though--only by people with access to the\nfilesystem.) So you have to leave the permissions at the socially friendly 0755 level.\n\nSome people regard this as a security problem. If your program does insecure things and\nrelies on people not knowing how to exploit those insecurities, it is not secure. It is often\npossible for someone to determine the insecure things and exploit them without viewing the\nsource. Security through obscurity, the name for hiding your bugs instead of fixing them, is\nlittle security indeed.\n\nYou can try using encryption via source filters (Starting from Perl 5.8 the Filter::Simple\nand Filter::Util::Call modules are included in the standard distribution), but any decent\nprogrammer will be able to decrypt it. You can try using the byte code compiler and\ninterpreter described later in perlfaq3, but the curious might still be able to de-compile\nit. You can try using the native-code compiler described later, but crackers might be able to\ndisassemble it. These pose varying degrees of difficulty to people wanting to get at your\ncode, but none can definitively conceal it (true of every language, not just Perl).\n\nIt is very easy to recover the source of Perl programs. You simply feed the program to the\nperl interpreter and use the modules in the B:: hierarchy. The B::Deparse module should be\nable to defeat most attempts to hide source. Again, this is not unique to Perl.\n\nIf you're concerned about people profiting from your code, then the bottom line is that\nnothing but a restrictive license will give you legal security. License your software and\npepper it with threatening statements like \"This is unpublished proprietary software of XYZ\nCorp. Your access to it does not give you permission to use it blah blah blah.\" We are not\nlawyers, of course, so you should see a lawyer if you want to be sure your license's wording\nwill stand up in court.\n\n#### How can I compile my Perl program into byte code or C?\n\n(contributed by brian d foy)\n\nIn general, you can't do this. There are some things that may work for your situation though.\nPeople usually ask this question because they want to distribute their works without giving\naway the source code, and most solutions trade disk space for convenience. You probably\nwon't see much of a speed increase either, since most solutions simply bundle a Perl\ninterpreter in the final product (but see \"How can I make my Perl program run faster?\").\n\nThe Perl Archive Toolkit is Perl's analog to Java's JAR. It's freely available and on CPAN (\n ).\n\nThere are also some commercial products that may work for you, although you have to buy a\nlicense for them.\n\nThe Perl Dev Kit ( ) from ActiveState can\n\"Turn your Perl programs into ready-to-run executables for HP-UX, Linux, Solaris and\nWindows.\"\n\nPerl2Exe ( ) is a command line program for\nconverting perl scripts to executable files. It targets both Windows and Unix platforms.\n\n#### How can I get \"#!perl\" to work on [MS-DOS,NT,...]?\n\nFor OS/2 just use\n\nextproc perl -S -yourswitches\n\nas the first line in \"*.cmd\" file (\"-S\" due to a bug in cmd.exe's \"extproc\" handling). For\nDOS one should first invent a corresponding batch file and codify it in \"ALTERNATESHEBANG\"\n(see the dosish.h file in the source distribution for more information).\n\nThe Win95/NT installation, when using the ActiveState port of Perl, will modify the Registry\nto associate the \".pl\" extension with the perl interpreter. If you install another port,\nperhaps even building your own Win95/NT Perl from the standard sources by using a Windows\nport of gcc (e.g., with cygwin or mingw32), then you'll have to modify the Registry yourself.\nIn addition to associating \".pl\" with the interpreter, NT people can use: \"SET\nPATHEXT=%PATHEXT%;.PL\" to let them run the program \"install-linux.pl\" merely by typing\n\"install-linux\".\n\nUnder \"Classic\" MacOS, a perl program will have the appropriate Creator and Type, so that\ndouble-clicking them will invoke the MacPerl application. Under Mac OS X, clickable apps can\nbe made from any \"#!\" script using Wil Sanchez' DropScript utility:\n .\n\nIMPORTANT!: Whatever you do, PLEASE don't get frustrated, and just throw the perl interpreter\ninto your cgi-bin directory, in order to get your programs working for a web server. This is\nan EXTREMELY big security risk. Take the time to figure out how to do it correctly.\n\n#### Can I write useful Perl programs on the command line?\n\nYes. Read perlrun for more information. Some examples follow. (These assume standard Unix\nshell quoting rules.)\n\n# sum first and last fields\nperl -lane 'print $F[0] + $F[-1]' *\n\n# identify text files\nperl -le 'for(@ARGV) {print if -f && -T }' *\n\n# remove (most) comments from C program\nperl -0777 -pe 's{/\\*.*?\\*/}{}gs' foo.c\n\n# make file a month younger than today, defeating reaper daemons\nperl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *\n\n# find first unused uid\nperl -le '$i++ while getpwuid($i); print $i'\n\n# display reasonable manpath\necho $PATH | perl -nl -072 -e '\ns![^/+]*$!man!&&-d&&!$s{$}++&&push@m,$;END{print\"@m\"}'\n\nOK, the last one was actually an Obfuscated Perl Contest entry. :-)\n\n#### Why don't Perl one-liners work on my DOS/Mac/VMS system?\n\nThe problem is usually that the command interpreters on those systems have rather different\nideas about quoting than the Unix shells under which the one-liners were created. On some\nsystems, you may have to change single-quotes to double ones, which you must NOT do on Unix\nor Plan9 systems. You might also have to change a single % to a %%.\n\nFor example:\n\n# Unix (including Mac OS X)\nperl -e 'print \"Hello world\\n\"'\n\n# DOS, etc.\nperl -e \"print \\\"Hello world\\n\\\"\"\n\n# Mac Classic\nprint \"Hello world\\n\"\n(then Run \"Myscript\" or Shift-Command-R)\n\n# MPW\nperl -e 'print \"Hello world\\n\"'\n\n# VMS\nperl -e \"print \"\"Hello world\\n\"\"\"\n\nThe problem is that none of these examples are reliable: they depend on the command\ninterpreter. Under Unix, the first two often work. Under DOS, it's entirely possible that\nneither works. If 4DOS was the command shell, you'd probably have better luck like this:\n\nperl -e \"print \"Hello world\\n\"\"\n\nUnder the Mac, it depends which environment you are using. The MacPerl shell, or MPW, is much\nlike Unix shells in its support for several quoting variants, except that it makes free use\nof the Mac's non-ASCII characters as control characters.\n\nUsing qq(), q(), and qx(), instead of \"double quotes\", 'single quotes', and `backticks`, may\nmake one-liners easier to write.\n\nThere is no general solution to all of this. It is a mess.\n\n[Some of this answer was contributed by Kenneth Albanowski.]\n\n#### Where can I learn about CGI or Web programming in Perl?\n\nFor modules, get the CGI or LWP modules from CPAN. For textbooks, see the two especially\ndedicated to web stuff in the question on books. For problems and questions related to the\nweb, like \"Why do I get 500 Errors\" or \"Why doesn't it run from the browser right when it\nruns fine on the command line\", see the troubleshooting guides and references in perlfaq9 or\nin the CGI MetaFAQ:\n\nL\n\nLooking into and modern Perl web frameworks is highly recommended,\nthough; web programming in Perl has evolved a long way from the old days of simple CGI\nscripts.\n\n#### Where can I learn about object-oriented Perl programming?\n\nA good place to start is perlootut, and you can use perlobj for reference.\n\nA good book on OO on Perl is the \"Object-Oriented Perl\" by Damian Conway from Manning\nPublications, or \"Intermediate Perl\" by Randal Schwartz, brian d foy, and Tom Phoenix from\nO'Reilly Media.\n\n#### Where can I learn about linking C with Perl?\n\nIf you want to call C from Perl, start with perlxstut, moving on to perlxs, xsubpp, and\nperlguts. If you want to call Perl from C, then read perlembed, perlcall, and perlguts. Don't\nforget that you can learn a lot from looking at how the authors of existing extension modules\nwrote their code and solved their problems.\n\nYou might not need all the power of XS. The Inline::C module lets you put C code directly in\nyour Perl source. It handles all the magic to make it work. You still have to learn at least\nsome of the perl API but you won't have to deal with the complexity of the XS support files.\n\n#### I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing\n\n#### wrong?\n\nDownload the ExtUtils::Embed kit from CPAN and run `make test'. If the tests pass, read the\npods again and again and again. If they fail, submit a bug report to\n with the output of \"make test TESTVERBOSE=1\" along\nwith \"perl -V\".\n\n#### When I tried to run my script, I got this message. What does it mean?\n\nA complete list of Perl's error messages and warnings with explanatory text can be found in\nperldiag. You can also use the splain program (distributed with Perl) to explain the error\nmessages:\n\nperl program 2>diag.out\nsplain [-v] [-p] diag.out\n\nor change your program to explain the messages for you:\n\nuse diagnostics;\n\nor\n\nuse diagnostics -verbose;\n\n#### What's MakeMaker?\n\n(contributed by brian d foy)\n\nThe ExtUtils::MakeMaker module, better known simply as \"MakeMaker\", turns a Perl script,\ntypically called \"Makefile.PL\", into a Makefile. The Unix tool \"make\" uses this file to\nmanage dependencies and actions to process and install a Perl distribution.\n\n### AUTHOR AND COPYRIGHT\n\nCopyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and other authors as noted. All\nrights reserved.\n\nThis documentation is free; you can redistribute it and/or modify it under the same terms as\nPerl itself.\n\nIrrespective of its distribution, all code examples here are in the public domain. You are\npermitted and encouraged to use this code and any derivatives thereof in your own programs\nfor fun or for profit as you see fit. A simple comment in the code giving credit to the FAQ\nwould be courteous but is not required.\n\n\n\nperl v5.34.0 2025-07-25 PERLFAQ3(1)\n\n" } ], "structuredContent": { "command": "PERLFAQ3", "section": "1", "mode": "man", "summary": "perlfaq3 - Programming Tools", "synopsis": null, "tldr_summary": null, "tldr_examples": [], "tldr_source": null, "flags": [], "examples": [], "see_also": [], "section_outline": [ { "name": "NAME", "lines": 2, "subsections": [] }, { "name": "VERSION", "lines": 2, "subsections": [] }, { "name": "DESCRIPTION", "lines": 3, "subsections": [ { "name": "How do I do (anything)?", "lines": 47 }, { "name": "How can I use Perl interactively?", "lines": 12 }, { "name": "How do I find which modules are installed on my system?", "lines": 62 }, { "name": "How do I debug my Perl programs?", "lines": 34 }, { "name": "How do I profile my Perl programs?", "lines": 32 }, { "name": "How do I cross-reference my Perl programs?", "lines": 4 }, { "name": "Is there a pretty-printer (formatter) for Perl?", "lines": 19 }, { "name": "Is there an IDE or Windows Perl Editor?", "lines": 149 }, { "name": "Where can I get Perl macros for vi?", "lines": 6 }, { "name": "Where can I get perl-mode or cperl-mode for emacs?", "lines": 9 }, { "name": "How can I use curses with Perl?", "lines": 5 }, { "name": "How can I write a GUI (X, Tk, Gtk, etc.) in Perl?", "lines": 45 }, { "name": "How can I make my Perl program run faster?", "lines": 23 }, { "name": "How can I make my Perl program take less memory?", "lines": 99 }, { "name": "Is it safe to return a reference to local or lexical data?", "lines": 15 }, { "name": "How can I free an array or hash so my program shrinks?", "lines": 18 }, { "name": "How can I make my CGI script more efficient?", "lines": 32 }, { "name": "How can I hide the source for my Perl program?", "lines": 33 }, { "name": "How can I compile my Perl program into byte code or C?", "lines": 21 }, { "name": "How can I get \"#!perl\" to work on [MS-DOS,NT,...]?", "lines": 25 }, { "name": "Can I write useful Perl programs on the command line?", "lines": 24 }, { "name": "Why don't Perl one-liners work on my DOS/Mac/VMS system?", "lines": 40 }, { "name": "Where can I learn about CGI or Web programming in Perl?", "lines": 12 }, { "name": "Where can I learn about object-oriented Perl programming?", "lines": 6 }, { "name": "Where can I learn about linking C with Perl?", "lines": 9 }, { "name": "I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing", "lines": 1 }, { "name": "wrong?", "lines": 5 }, { "name": "When I tried to run my script, I got this message. What does it mean?", "lines": 15 }, { "name": "What's MakeMaker?", "lines": 6 } ] }, { "name": "AUTHOR AND COPYRIGHT", "lines": 14, "subsections": [] } ] } }