Perl 5 version 6.0 documentation



perl - Practical Extraction and Report Language


perl [ -sTuU ] [ -hv ] [ -V[:configvar] ] [ -cw ] [ -d[:debugger] ] [ -D[number/list] ] [ -pna ] [ -Fpattern ] [ -l[octal] ] [ -0[octal] ] [ -Idir ] [ -m[-]module ] [ -M[-]'module...' ] [ -P ] [ -S ] [ -x[dir] ] [ -i[extension] ] [ -e 'command' ] [ -- ] [ programfile ] [ argument ]...

For ease of access, the Perl manual has been split up into several sections:

  1. perl Perl overview (this section)
  2. perldelta Perl changes since previous version
  3. perl5005delta Perl changes in version 5.005
  4. perl5004delta Perl changes in version 5.004
  5. perlfaq Perl frequently asked questions
  6. perltoc Perl documentation table of contents
  7. perldata Perl data structures
  8. perlsyn Perl syntax
  9. perlop Perl operators and precedence
  10. perlre Perl regular expressions
  11. perlrun Perl execution and options
  12. perlfunc Perl builtin functions
  13. perlopentut Perl open() tutorial
  14. perlvar Perl predefined variables
  15. perlsub Perl subroutines
  16. perlmod Perl modules: how they work
  17. perlmodlib Perl modules: how to write and use
  18. perlmodinstall Perl modules: how to install from CPAN
  19. perlform Perl formats
  20. perlunicode Perl unicode support
  21. perllocale Perl locale support
  22. perlreftut Perl references short introduction
  23. perlref Perl references, the rest of the story
  24. perldsc Perl data structures intro
  25. perllol Perl data structures: arrays of arrays
  26. perlboot Perl OO tutorial for beginners
  27. perltoot Perl OO tutorial, part 1
  28. perltootc Perl OO tutorial, part 2
  29. perlobj Perl objects
  30. perltie Perl objects hidden behind simple variables
  31. perlbot Perl OO tricks and examples
  32. perlipc Perl interprocess communication
  33. perlfork Perl fork() information
  34. perlthrtut Perl threads tutorial
  35. perllexwarn Perl warnings and their control
  36. perlfilter Perl source filters
  37. perldbmfilter Perl DBM filters
  38. perlcompile Perl compiler suite intro
  39. perldebug Perl debugging
  40. perldiag Perl diagnostic messages
  41. perlnumber Perl number semantics
  42. perlsec Perl security
  43. perltrap Perl traps for the unwary
  44. perlport Perl portability guide
  45. perlstyle Perl style guide
  46. perlpod Perl plain old documentation
  47. perlbook Perl book information
  48. perlembed Perl ways to embed perl in your C or C++ application
  49. perlapio Perl internal IO abstraction interface
  50. perldebguts Perl debugging guts and tips
  51. perlxs Perl XS application programming interface
  52. perlxstut Perl XS tutorial
  53. perlguts Perl internal functions for those doing extensions
  54. perlcall Perl calling conventions from C
  55. perlapi Perl API listing (autogenerated)
  56. perlintern Perl internal functions (autogenerated)
  57. perltodo Perl things to do
  58. perlhack Perl hackers guide
  59. perlhist Perl history records
  60. perlamiga Perl notes for Amiga
  61. perlcygwin Perl notes for Cygwin
  62. perldos Perl notes for DOS
  63. perlhpux Perl notes for HP-UX
  64. perlmachten Perl notes for Power MachTen
  65. perlos2 Perl notes for OS/2
  66. perlos390 Perl notes for OS/390
  67. perlvms Perl notes for VMS
  68. perlwin32 Perl notes for Windows

(If you're intending to read these straight through for the first time, the suggested order will tend to reduce the number of forward references.)

By default, the manpages listed above are installed in the /usr/local/man/ directory.

Extensive additional documentation for Perl modules is available. The default configuration for perl will place this additional documentation in the /usr/local/lib/perl5/man directory (or else in the man subdirectory of the Perl library directory). Some of this additional documentation is distributed standard with Perl, but you'll also find documentation for third-party modules there.

You should be able to view Perl's documentation with your man(1) program by including the proper directories in the appropriate start-up files, or in the MANPATH environment variable. To find out where the configuration has installed the manpages, type:

  1. perl -V:man.dir

If the directories have a common stem, such as /usr/local/man/man1 and /usr/local/man/man3, you need only to add that stem (/usr/local/man) to your man(1) configuration files or your MANPATH environment variable. If they do not share a stem, you'll have to add both stems.

If that doesn't work for some reason, you can still use the supplied perldoc script to view module information. You might also look into getting a replacement man program.

If something strange has gone wrong with your program and you're not sure where you should look for help, try the -w switch first. It will often point out exactly where the trouble is.


Perl is a language optimized for scanning arbitrary text files, extracting information from those text files, and printing reports based on that information. It's also a good language for many system management tasks. The language is intended to be practical (easy to use, efficient, complete) rather than beautiful (tiny, elegant, minimal).

Perl combines (in the author's opinion, anyway) some of the best features of C, sed, awk, and sh, so people familiar with those languages should have little difficulty with it. (Language historians will also note some vestiges of csh, Pascal, and even BASIC-PLUS.) Expression syntax corresponds closely to C expression syntax. Unlike most Unix utilities, Perl does not arbitrarily limit the size of your data--if you've got the memory, Perl can slurp in your whole file as a single string. Recursion is of unlimited depth. And the tables used by hashes (sometimes called "associative arrays") grow as necessary to prevent degraded performance. Perl can use sophisticated pattern matching techniques to scan large amounts of data quickly. Although optimized for scanning text, Perl can also deal with binary data, and can make dbm files look like hashes. Setuid Perl scripts are safer than C programs through a dataflow tracing mechanism that prevents many stupid security holes.

If you have a problem that would ordinarily use sed or awk or sh, but it exceeds their capabilities or must run a little faster, and you don't want to write the silly thing in C, then Perl may be for you. There are also translators to turn your sed and awk scripts into Perl scripts.

But wait, there's more...

Begun in 1993 (see perlhist), Perl version 5 is nearly a complete rewrite that provides the following additional benefits:

Okay, that's definitely enough hype.


Perl is available for most operating systems, including virtually all Unix-like platforms. See Supported Platforms in perlport for a listing.


See perlrun.


Larry Wall <>, with the help of oodles of other folks.

If your Perl success stories and testimonials may be of help to others who wish to advocate the use of Perl in their applications, or if you wish to simply express your gratitude to Larry and the Perl developers, please write to .


  1. "@INC" locations of perl libraries


  1. a2p awk to perl translator
  2. s2p sed to perl translator
  3. the Perl Home Page
  4. the Comprehensive Perl Archive


The use warnings pragma (and the -w switch) produces some lovely diagnostics.

See perldiag for explanations of all Perl's diagnostics. The use diagnostics pragma automatically turns Perl's normally terse warnings and errors into these longer forms.

Compilation errors will tell you the line number of the error, with an indication of the next token or token type that was to be examined. (In a script passed to Perl via -e switches, each -e is counted as one line.)

Setuid scripts have additional constraints that can produce error messages such as "Insecure dependency". See perlsec.

Did we mention that you should definitely consider using the -w switch?


The -w switch is not mandatory.

Perl is at the mercy of your machine's definitions of various operations such as type casting, atof(), and floating-point output with sprintf().

If your stdio requires a seek or eof between reads and writes on a particular stream, so does Perl. (This doesn't apply to sysread() and syswrite().)

While none of the built-in data types have any arbitrary size limits (apart from memory size), there are still a few arbitrary limits: a given variable name may not be longer than 251 characters. Line numbers displayed by diagnostics are internally stored as short integers, so they are limited to a maximum of 65535 (higher numbers usually being affected by wraparound).

You may mail your bug reports (be sure to include full configuration information as output by the myconfig program in the perl source tree, or by perl -V ) to . If you've succeeded in compiling perl, the perlbug script in the utils/ subdirectory can be used to help mail in a bug report.

Perl actually stands for Pathologically Eclectic Rubbish Lister, but don't tell anyone I said that.


The Perl motto is "There's more than one way to do it." Divining how many more is left as an exercise to the reader.

The three principal virtues of a programmer are Laziness, Impatience, and Hubris. See the Camel Book for why.