Perl 5 version 6.1 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. perlfaq Perl frequently asked questions
  3. perltoc Perl documentation table of contents
  4. perlbook Perl book information
  5. perlsyn Perl syntax
  6. perldata Perl data structures
  7. perlop Perl operators and precedence
  8. perlsub Perl subroutines
  9. perlfunc Perl builtin functions
  10. perlreftut Perl references short introduction
  11. perldsc Perl data structures intro
  12. perlrequick Perl regular expressions quick start
  13. perlpod Perl plain old documentation
  14. perlstyle Perl style guide
  15. perltrap Perl traps for the unwary
  16. perlrun Perl execution and options
  17. perldiag Perl diagnostic messages
  18. perllexwarn Perl warnings and their control
  19. perldebtut Perl debugging tutorial
  20. perldebug Perl debugging
  21. perlvar Perl predefined variables
  22. perllol Perl data structures: arrays of arrays
  23. perlopentut Perl open() tutorial
  24. perlretut Perl regular expressions tutorial
  25. perlre Perl regular expressions, the rest of the story
  26. perlref Perl references, the rest of the story
  27. perlform Perl formats
  28. perlboot Perl OO tutorial for beginners
  29. perltoot Perl OO tutorial, part 1
  30. perltootc Perl OO tutorial, part 2
  31. perlobj Perl objects
  32. perlbot Perl OO tricks and examples
  33. perltie Perl objects hidden behind simple variables
  34. perlipc Perl interprocess communication
  35. perlfork Perl fork() information
  36. perlnumber Perl number semantics
  37. perlthrtut Perl threads tutorial
  38. perlport Perl portability guide
  39. perllocale Perl locale support
  40. perlunicode Perl unicode support
  41. perlebcdic Considerations for running Perl on EBCDIC platforms
  42. perlsec Perl security
  43. perlmod Perl modules: how they work
  44. perlmodlib Perl modules: how to write and use
  45. perlmodinstall Perl modules: how to install from CPAN
  46. perlnewmod Perl modules: preparing a new module for distribution
  47. perlfaq1 General Questions About Perl
  48. perlfaq2 Obtaining and Learning about Perl
  49. perlfaq3 Programming Tools
  50. perlfaq4 Data Manipulation
  51. perlfaq5 Files and Formats
  52. perlfaq6 Regexes
  53. perlfaq7 Perl Language Issues
  54. perlfaq8 System Interaction
  55. perlfaq9 Networking
  56. perlcompile Perl compiler suite intro
  57. perlembed Perl ways to embed perl in your C or C++ application
  58. perldebguts Perl debugging guts and tips
  59. perlxstut Perl XS tutorial
  60. perlxs Perl XS application programming interface
  61. perlclib Internal replacements for standard C library functions
  62. perlguts Perl internal functions for those doing extensions
  63. perlcall Perl calling conventions from C
  64. perlutil utilities packaged with the Perl distribution
  65. perlfilter Perl source filters
  66. perldbmfilter Perl DBM filters
  67. perlapi Perl API listing (autogenerated)
  68. perlintern Perl internal functions (autogenerated)
  69. perlapio Perl internal IO abstraction interface
  70. perltodo Perl things to do
  71. perlhack Perl hackers guide
  72. perlhist Perl history records
  73. perldelta Perl changes since previous version
  74. perl5005delta Perl changes in version 5.005
  75. perl5004delta Perl changes in version 5.004
  76. perlaix Perl notes for AIX
  77. perlamiga Perl notes for Amiga
  78. perlbs2000 Perl notes for POSIX-BC BS2000
  79. perlcygwin Perl notes for Cygwin
  80. perldos Perl notes for DOS
  81. perlepoc Perl notes for EPOC
  82. perlhpux Perl notes for HP-UX
  83. perlmachten Perl notes for Power MachTen
  84. perlmacos Perl notes for Mac OS (Classic)
  85. perlmpeix Perl notes for MPE/iX
  86. perlos2 Perl notes for OS/2
  87. perlos390 Perl notes for OS/390
  88. perlsolaris Perl notes for Solaris
  89. perlvmesa Perl notes for VM/ESA
  90. perlvms Perl notes for VMS
  91. perlvos Perl notes for Stratus VOS
  92. 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.