Perl FAQ

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Introduction

Hear ye, hear ye. This most honourable session on Perl Frequently Asked Questions is hereby called to order. Please stand and show your respect for those that have gone before us. Let us honour Larry Wall*, the father of Perl who unselfishly spends vast amounts of time reviewing this document for veracity and accuracy. Let us also honour Tom Christiansen* without whom this document would not exist. Finally, let us collectively honour the members of comp.lang.perl who have offered much advice and corrections to this list.

This article details the contents of the most Frequently Asked Questions in comp.lang.perl, a Usenet newsgroup devoted to the Perl programming language. There are five pieces following this, the general information questions in part1, part2 and part3 and the programming ones in part4 and part5.

If this is your first exposure to Perl, please read this document and the perl(1) man page before asking questions in comp.lang.perl. If you're using v4 perl, that page contains all you need to know (or at least enough to get started). If you're using v5 perl, that page will show you where to look for specific information. When we refer to perlmod(1), it means the "perlmod" man page in section "1" of the manual, just as Foo(3pm), that means it's the "Foo" man page in section "3pm" (perl modules) of the library. The perl install does NOT automatically install the module man pages for you, however.

Hopefully the questions herein are asked enough that considerable net bandwidth can be saved by looking here before asking. Also, hopefully there is enough information contained here that someone who has never heard of Perl can read this and at least have some sort of idea as to what Perl is.

Some questions in this group aren't really about Perl, but rather about system-specific issues. You might also consult the Most Frequently Asked Questions list in comp.unix.questions for answers to this type of question.

The current version of perl is 5.001, perl 5.000 emerged into the world on 16 October, 1994. The previous non-beta version was 4.036 (version 4, patchlevel 36). Many of these questions were written for perl4, however a lot of perl5 information has also been added. Perl5 only features will be clearly marked as such, so as not to cause confusion for those still using perl4. You should upgrade to perl5 as soon as possible though (see below).

This list was initially written, and still hacked upon, by Tom Christiansen*. However, due to his erratic schedule, it is currently maintained by Stephen P Potter*. First person singular pronouns, when not in quoted postings, generally are Tom talking.

This document, and all its parts, are Copyright (c) 1994/1995, Stephen P Potter and Tom Christiansen, perlfaq@perl.com. All rights reservered. Permisson to distribute this collection, in part or full, via electronic means (emailed, posted or archived) or printed copy are granted providing that no charges are involved, reasonable attempt is made to use the most current version, and all credits and copyright notices are retained. Requests for other distribution rights, including incorporation in commercial products, such as books, magazine articles, or CD-ROMs should be made to perlfaq@perl.com.

This FAQ is archived on ftp.cis.ufl.edu [128.227.100.198] in the file pub/perl/doc/FAQ, as well as on rtfm.mit.edu [18.181.0.24] in pub/usenet/comp.lang.perl. If you have any suggested additions or corrections to this article, please send them to <perlfaq@perl.com>.

Table of Contents

Availability

Questions

• 1.1: What is Perl?
• 1.2: What are perl4 and perl5, are there any differences?
• 1.3: What features does perl5 provide over perl4?
• 1.4: Where can I get docs on perl5?
• 1.5: Will perl5 break my perl4 scripts?
• 1.6: When will Perl stabilize?
• 1.7: What's the difference between "perl" and "Perl"?
• 1.8: Is it a perl program or a perl script?
• 1.9: Is perl difficult to learn?
• 1.10: Should I program everything in Perl?
• 1.11: How does Perl compare with other scripting languages, like Tcl, Python or REXX?
• 1.12: How can I get Perl over the Internet?
• 1.13: How can I get Perl via Email?
• 1.14: How can I get Perl via UUCP?
• 1.15: Are there other ways of getting perl?
• 1.16: Has perl been ported to machine FOO?
• 1.17: How do I get Perl to compile on Solaris?
• 1.18: How do I get Perl to compile on a Next?
• 1.19: What extensions are available from Perl and where can I get them?
• 1.20: What is dbperl and where can I get it?
• 1.21: Which DBM should I use?
• 1.22: Is there an SNMP aware Perl?
• 1.23: Is there an ISO or ANSI certified version of Perl?

Information Sources

Questions

• 2.1: Is there a USENET group for Perl?
• 2.2: Have any books or magazine articles been published about Perl?
• 2.3: When will the Camel and Llama books be updated?
• 2.4: What FTP resources are available?
• 2.5: What WWW/gopher resources are available?
• 2.6: Can people who don't have access to USENET get comp.lang.perl?
• 2.7: Are archives of comp.lang.perl available?
• 2.8: Is there a WAIS server for comp.lang.perl?
• 2.9: What other sources of information about Perl or training are available?
• 2.10: Where can I get training classes on Perl?
• 2.11: What companies use or ship Perl?
• 2.12: Is there commercial, third-party support for Perl?
• 2.13: What is a JAPH? What does "Will hack perl for ..." mean?
• 2.14: Where can I get a list of Larry Wall witticisms?
• 2.15: What are the known bugs?
• 2.16: Where should I post bugs?
• 2.17: Where should I post source code?
• 2.18: Where can I learn about object-oriented Perl programming?
• 2.19: Where can I learn about linking C with Perl? [h2xs, xsubpp]
• 2.20: What is perl.com?
• 2.21: What do the asterisks (*) throughout the FAQ stand for?

Programming Aids

Questions

• 3.1: How can I use Perl interactively?
• 3.2: Is there a Perl profiler?
• 3.3: Is there a yacc for Perl?
• 3.4: Is there a pretty-printer (similar to indent(1)) for Perl?
• 3.5: How can I convert my perl scripts directly to C or compile them into binary form?
• 3.6: Where can I get a perl-mode for emacs?
• 3.7: Is there a Perl shell?
• 3.8: How can I use curses with perl?
• 3.9: How can I use X or Tk with Perl?
• 3.10: Can I dynamically load C user routines?
• 3.11: What is undump and where can I get it?
• 3.12: How can I get '#!perl' to work under MS-DOS?
• 3.13: Can I write useful perl programs on the command line?
• 3.14: What's a "closure"?

General Programming

Questions

• 4.1: What are all these $@%*<> signs and how do I know when to use them?
• 4.2: How come Perl operators have different precedence than C operators?
• 4.3: What's the difference between dynamic and static (lexical) scoping? What are my() and local()?
• 4.4: What's the difference between deep and shallow binding?
• 4.5: How can I manipulate fixed-record-length files?
• 4.6: How can I make a file handle local to a subroutine?
• 4.7: How can I call alarm() or usleep() from Perl?
• 4.8: How can I do an atexit() or setjmp()/longjmp() in Perl? (Exception handling)
• 4.9: How do I catch signals in perl?
• 4.10: Why doesn't Perl interpret my octal data octally?
• 4.11: How can I compare two date strings?
• 4.12: How can I find the Julian Day?
• 4.13: Does perl have a round function? What about ceil() and floor()?
• 4.14: What's the fastest way to code up a given task in perl?
• 4.15: Do I always/never have to quote my strings or use semicolons?
• 4.16: What is variable suicide and how can I prevent it?
• 4.17: What does "Malformed command links" mean?
• 4.18: How can I set up a footer format to be used with write()?
• 4.19: Why does my Perl program keep growing in size?
• 4.20: Can I do RPC in Perl?
• 4.21: Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean?
• 4.22: How can I quote a variable to use in a regexp?
• 4.23: How can I change the first N letters of a string?
• 4.24: How can I count the number of occurrences of a substring within a string?
• 4.25: Can I use Perl regular expressions to match balanced text?
• 4.26: What does it mean that regexps are greedy? How can I get around it?
• 4.27: How do I use a regular expression to strip C style comments from a file?
• 4.28: How can I split a [character] delimited string except when inside [character]?
• 4.29: Why doesn't "local($foo) = <FILE>;" work right?
• 4.30: How can I detect keyboard input without reading it?
• 4.31: How can I read a single character from the keyboard under UNIX and DOS?
• 4.32: How can I get input from the keyboard without it echoing to the screen?
• 4.33: Is there any easy way to strip blank space from the beginning/end of a string?
• 4.34: How can I print out a number with commas into it?
• 4.35: How do I expand tabs in a string?
• 4.36: What's wrong with grep() or map() in a void context?

External Program Interaction

Questions

• 5.1: What is the difference between $array[1] and @array[1]?
• 5.2: How can I make an array of arrays or other recursive data types?
• 5.3: How do I make an array of structures containing various data types?
• 5.4: How can I extract just the unique elements of an array?
• 5.5: How can I tell whether an array contains a certain element?
• 5.6: How do I sort an associative array by value instead of by key?
• 5.7: How can I know how many entries are in an associative array?
• 5.8: What's the difference between "delete" and "undef" with %arrays?
• 5.9: Why don't backticks work as they do in shells?
• 5.10: How come my converted awk/sed/sh script runs more slowly in Perl?
• 5.11: How can I call my system's unique C functions from Perl?
• 5.12: Where do I get the include files to do ioctl() or syscall()? [h2ph]
• 5.13: Why do setuid Perl scripts complain about kernel problems?
• 5.14: How do I open a pipe both to and from a command?
• 5.15: How can I capture STDERR from an external command?
• 5.16: Why doesn't open return an error when a pipe open fails?
• 5.17: Why can't my perl program read from STDIN after I gave it ^D (EOF) ?
• 5.18: How can I translate tildes in a filename?
• 5.19: How can I convert my shell script to Perl?
• 5.20: Can I use Perl to run a telnet or ftp session?
• 5.21: Why do I sometimes get an "Arguments too long" error when I use <*>?
• 5.22: How do I do a "tail -f" in Perl?
• 5.23: Is there a way to hide perl's command line from programs such as "ps"?
• 5.24: I {changed directory, modified my environment} in a perl script. How come the change disappeared when I exited the script? How do I get my changes to be visible?
• 5.25: How can I use pass a filehandle to a function, or make a list of filehandles?
• 5.26: How can open a file with a leading ">" or trailing blanks?
• 5.27: How can I tell if a variable is tainted?

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