Rex Swain's HTMLified
Perl 5 Reference Guide

Last updated 22 March 2001
[Links updated 7 September 2003]

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This is an HTMLified version of the Perl 5 Desktop Reference, ISBN 1-56592-187-9, copyright © 1996 by Johan Vromans. HTML copyright © 1996-2000 by Rex Swain.

See Perl 5 Desktop Reference for information about ordering a printed copy ($6.95) of the booklet from O'Reilly. [But it's no longer in print -- instead, get the Perl 5 Pocket Reference, 2nd Edition, updated for Perl version 5.005.] [Now there is a 3rd Edition, revised to cover Perl version 5.6.] [Now there is a 4th Edition, revised to cover Perl version 5.8.]

See The Perl Reference Guide for links to other online versions in various formats (PostScript, PDF, etc.).

For more detail, see Perl Documentation.


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abs  accept  alarm  and  ARGV  ArithmeticFunctions  ArrayListFunctions  ArraysSpecial  atan2  BEGIN  bind  binmode  bless  caller  chdir  chmod  chomp  chop  chr  chroot  close  closedir  cmp  CommandLineOptions  connect  Contents  continue  Conventions  ConversionFunctions  ConversionStructure  cos  crypt  dbmclose  dbmopen  Debugger  defined  delete  die  DirectoryReadingRoutines  do  do  do  dump  each  else  elsif  END  ENV  EnvironmentVariables  eof  eq  eval  eval  exec  exists  exit  exp  EXPORT  EXPORT_OK  ExpressionsRegular  fcntl  fileno  FileOperations  FilesSystemInformationFrom  FileTestOperators  flock  for  foreach  fork  Formats  formline  FunctionsArithmetic  FunctionsArrayList  FunctionsConversion  FunctionsSearchReplace  FunctionsString  ge  getc  getlogin  getpeername  getpgrp  getppid  getpriority  getsockname  getsockopt  glob  gmtime  goto  goto  grep  gt  hex  HOME  if  import  INC  Index  index  InformationFromSystemFiles  InputOutput  int  InteractionSystem  ioctl  ISA  join  keys  kill  last  lc  lcfirst  le  length  link  ListArrayFunctions  listen  Literals  local  localtime  log  LOGDIR  lstat  lt  m  map  Miscellaeous  mkdir  Modules  my  ne  Networking  next  no  npt  ObjectOrientedProgramming  oct  open  opendir  OperationsFile  Operators  OperatorsFileTest  OptionsCommandLine  or  ord  OutputInput  OVERLOAD  pack  package  Packages  PATH  PERL5DB  PERL5LIB  PERLLIB  pipe  pop  pos  print  printf  push  quotemeta  rand  read  readdir  ReadingDirectoryRoutines  readlink  recv  redo  ref  RegularExpressions  rename  ReplaceSearchFunctions  require  reset  return  reverse  rewindir  rindex  rmdir  RoutinesDirectoryReading  s  scalar  scalar  SearchReplaceFunctions  seek  seekdir  select  send  setpgrp  setpriority  setsockopt  shift  shutdown  SIG  sin  sleep  socket  socketpair  sort  SpecialArrays  SpecialVariables  splice  split  sprintf  sqrt  srand  stat  Statements  StringFunctions  StructureConversion  study  sub  Subroutines  substr  symlink  syscall  sysread  system  SystemFilesInformationFrom  SystemInteraction  SystemVIPC  syswrite  tell  telldir  TestFileOperators  tie  time  times  tr  truncate  uc  ucfirst  umask  undef  unless  unlink  unpack  unshift  untie  until  until  use  utime  values  Variables  VariablesEnvironment  VariablesSpecial  vec  wait  waitpid  wantarray  warn  while  write  xor  y 

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fixed   denotes literal text.
THIS means variable text, i.e., things you must fill in.
THIS† means that THIS will default to $_ if omitted.
word is a keyword, i.e., a word with a special meaning.
RETURN key   denotes pressing a keyboard key.
[...] denotes an optional part.

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Command-Line Options

turns on autosplit mode when used with -n or -p. Splits to @F.
checks syntax but does not execute.
runs the script under the debugger. Use -de 0 to start the debugger without a script
sets debugging flags.
may be used to enter a single line of script. Multiple -e commands may be given to build up a multiline script.
specifies a regular expression to split on if -a is in effect.
files processed by the < > construct are to be edited in place.
with -P, tells the C preprocessor where to look for include files. The directory is prepended to @INC.
enables automatic line-end processing, e.g., -l013.
assumes an input loop around your script. Lines are not printed.
assumes an input loop around your script. Lines are printed.
runs the C preprocessor on the script before compilation by Perl.
interprets -xxx on the command line as a switch and sets the corresponding variable $xxx in the script.
uses the PATH environment variable to search for the script.
forces taint checking.
dumps core after compiling the script. To be used with the undump(1) program (where available).
allows perl to perform unsafe operations.
prints the version and patchlevel of your Perl executable.
prints warnings about possible spelling errors and other error-prone constructs in the script.
-x [DIR]
extracts Perl program from input stream. If DIR is specified, switches to this directory before running the program.
(that's the number zero.) Designates an initial value for the record separator $/. See also -l

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0xff (hex)
0377 (octal)
literal string, no variable interpolation or escape characters, except \' and \\. Also: q/abc/. Almost any pair of delimiters can be used instead of /.../.
Variables are interpolated and escape sequences are processed. Also: qq/abc/.
Escape sequences: \t (Tab), \n (Newline), \r (Return), \f (Formfeed), \b (Backspace), \a (Alarm), \e (Escape), \033 (octal), \x1b (hex), \c[ (control)
\l and \u lowercase/uppercase the following character. \L and \U lowercase/uppercase until a \E is encountered. \Q quote regular expression characters until a \E is encountered.
evaluates to the output of the COMMAND. Also: qx/COMMAND/.
(1, 2, 3). () is an empty array.
(1..4) is the same as (1,2,3,4),
likewise ('a'..'z').
qw/foo bar .../ is the same as ('foo','bar',...).
Array reference:
Hash (associative array):
(KEY1, VAL1, KEY2, VAL2,...)
Also (KEY1=> VAL1, KEY2=> VAL2,...)
Hash reference:
{KEY1, VAL1, KEY2, VAL2,...}
Code reference:
User-specified: HANDLE, $VAR.
<PATTERN> evaluates to all filenames according to the pattern. Use <${VAR}> or glob $VAR to glob from a variable.
Shell-style "here document."
Special tokens:
__FILE__: filename; __LINE__: line number; __END__: end of program; remaining lines can be read using the filehandle DATA.

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$var a simple scalar variable.
$var[28] 29th element of array @var.
$p = \@var now $p is a reference to array @var.
$$p[28] 29th element of array referenced by $p.
Also, $p->[28].
$var[-1] last element of array @var.
$var[$i][$j] $jth element of the $ith element of array @var.
$var{'Feb'} one value from hash (associative array) %var.
$p = \%var now $p is a reference to hash %var.
$$p{'Feb'} a value from hash referenced by $p.
Also, $p->{'Feb'}.
$#var last index of array @var.
@var the entire array; in a scalar context, the number of elements in the array.
@var[3,4,5] a slice of array @var.
@var{'a','b'} a slice of %var; same as ($var{'a'},$var{'b'}).
%var the entire hash; in a scalar context, true if the hash has elements.
$var{'a',1,...} emulates a multidimensional array.
('a'...'z')[4,7,9] a slice of an array literal.
PKG::VAR a variable from a package, e.g., $pkg::var, @pkg::ary.
\OBJECT reference to an object, e.g., \$var, \%hash.
*NAME refers to all objects represented by NAME.
*n1 = *n2 makes n1 an alias for n2.
*n1 = $n2 makes $n1 an alias for $n2.

You can always use a {BLOCK} returning the right type of reference instead of the variable identifier, e.g., ${...}, &{...}. $$p is just a shorthand for ${$p}.

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** Exponentiation
+ -  * /  Addition, subtraction, multiplication, division
% Modulo division
& | ^ Bitwise AND, bitwise OR, bitwise exclusive OR
>> << Bitwise shift right, bitwise shift left
|| && Logical OR, logical AND
. Concatenation of two strings
x Returns a string or array consisting of the left operand (an array or a string) repeated the number of times specified by the right operand
All of the above operators also have an assignment operator, e.g., .=
-> Dereference operator
\ Reference (unary)
! ~ Negation (unary), bitwise complement (unary)
++ -- Auto-increment (magical on strings), auto-decrement
== != Numeric equality, inequality
eq ne String equality, inequality
< > Numeric less than, greater than
lt gt String less than, greater than
<= >= Numeric less (greater) than or equal to
le ge String less (greater) than or equal to
<=> cmp Numeric (string) compare. Returns -1, 0, 1.
=~ !~ Search pattern, substitution, or translation (negated)
.. Range (scalar context) or enumeration (array context)
?: Alternation (if-then-else) operator
, Comma operator, also list element separator. You can also use =>.
not Low-precedence negation
and Low-precedence AND
or xor Low-precedence OR, exclusive OR

All Perl functions can be used as list operators, in which case they have very high or very low precedence, depending on whether you look at the left or the right side of the operator. Only the operators not, and, or and xor have lower precedence.

A "list" is a list of expressions, variables, or lists. An array variable or an array slice may always be used instead of a list.

Parentheses can be added around the parameter lists to avoid precedence problems.

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Every statement is an expression, optionally followed by a modifier, and terminated by a semicolon. The semicolon may be omitted if the statement is the final one in a BLOCK.

Execution of expressions can depend on other expressions using one of the modifiers if, unless, while or until, for example:

The logical operators ||, && or ?: also allow conditional execution:

Statements can be combined to form a BLOCK when enclosed in {}. Blocks may be used to control flow:

Program flow can be controlled with:

Special forms are:

which are guaranteed to perform BLOCK once before testing EXPR, and

which effectively turns BLOCK into an expression.

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Subroutines, Packages and Modules

Executes a SUBROUTINE declared by a sub declaration, and returns the value of the last expression evaluated in SUBROUTINE. SUBROUTINE can be an expression yielding a reference to a code object. The & may be omitted if the subroutine has been declared before being used.
bless REF [ , PACKAGE ]
Turns the object REF into an object in PACKAGE. Returns the reference.
caller [ EXPR ]
Returns an array ($package,$file,$line,...) for a specific subroutine call. caller returns this info for the current subroutine, caller(1) for the caller of this subroutine, etc. Returns false if no caller.
Deprecated form of &SUBROUTINE.
Substitutes a call to SUBROUTINE for the current subroutine.
import MODULE [ [ VERSION ] LIST ]
Imports the named subroutines from MODULE.
Cancels imported semantics. See use.
package NAME
Designates the remainder of the current block as a package.
require EXPR†
If EXPR is numeric, requires Perl to be at least that version. Otherwise EXPR must be the name of a file that is included from the Perl library. Does not include more than once, and yields a fatal error if the file does not evaluate to a true value. If EXPR is a bare word, assumes extension .pm for the name of the file.
return EXPR
Returns from a subroutine with the value specified.
sub NAME { EXPR ; ... }
Designates NAME as a subroutine. Parameters are passed by reference as array @_. Returns the value of the last expression evaluated.
[ sub ] BEGIN { EXPR ; ... }
Defines a setup BLOCK to be called before execution.
[ sub ] END { EXPR ; ... }
Defines a cleanup BLOCK to be called upon termination.
Ties a variable to a package that will handle it. Can be used to bind a dbm or ndbm file to a hash.
untie VAR
Breaks the binding between the variable and the package.
Imports semantics from the named module into the current package.

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Object-Oriented Programming

Perl rules of object oriented programming:

Methods can be applied with:

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Arithmetic Functions

abs EXPR† Returns the absolute value of its operand.
atan2 Y,X Returns the arctangent of Y/X in the range -pi to pi.
cos EXPR† Returns the cosine of EXPR (expressed in radians).
exp EXPR† Returns e to the power of EXPR.
int EXPR† Returns the integer portion of EXPR.
log EXPR† Returns natural logarithm (base e) of EXPR.
rand [ EXPR ] Returns a random fractional number between 0 and the value of EXPR. If EXPR is omitted, returns a value between 0 and 1.
sin EXPR† Returns the sine of EXPR (expressed in radians).
sqrt EXPR† Returns the square root of EXPR.
srand [ EXPR ]    Sets the random number seed for the rand operator.
time Returns the number of seconds since January 1, 1970. Suitable for feeding to gmtime and localtime.

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Conversion Functions

chr EXPR†
Returns the character represented by the decimal value EXPR.
gmtime EXPR†
Converts a time as returned by the time function to a 9-element array (0: $sec, 1: $min, 2: $hour, 3: $mday, 4: $mon, 5: $year, 6: $wday, 7: $yday, 8: $isdst) with the time analyzed for the Greenwich time zone. $mon has the range 0..11 and $wday has the range 0..6.
hex EXPR†
Returns the decimal value of EXPR interpreted as a hex string.
localtime EXPR†
Converts a time as returned by the time function to ctime(3) string. In array context, returns a 9-element array with the time analyzed for the local time zone.
oct EXPR†
Returns the decimal value of EXPR interpreted as an octal string. If EXPR starts off with 0x, interprets it as a hex string instead.
ord EXPR†
Returns the ASCII value of the first character of EXPR.
Treats string EXPR as a vector of unsigned integers, and yields the bit at OFFSET. BITS must be between 1 and 32. May be assigned to.

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Structure Conversion

Packs the values into a binary structure using TEMPLATE.
Unpacks the structure EXPR into an array, using TEMPLATE.

TEMPLATE is a sequence of characters as follows:

Each character may be followed by a decimal number that will be used as a repeat count; an asterisk (*) specifies all remaining arguments. If the format is preceded with %N, unpack returns an N-bit checksum instead. Spaces may be included in the template for readability purposes.

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String Functions

chomp LIST†
Removes line endings from all elements of the list; returns the (total) number of characters removed.
chop LIST†
Chops off the last character on all elements of the list; returns the last chopped character.
Encrypts a string.
eval EXPR†
EXPR is parsed and executed as if it were a Perl program. The value returned is the value of the last expression evaluated. If there is a syntax error or runtime error, an undefined string is returned by eval, and $@ is set to the error message. See also eval in section Miscellaneous.
index STR, SUBSTR [ , OFFSET ]
Returns the position of SUBSTR in STR at or after OFFSET. If the substring is not found, returns -1 (but see $[ in section Special Variables).
length EXPR†
Returns the length in characters of the value of EXPR.
Returns a lowercase version of EXPR.
lcfirst EXPR
Returns EXPR with the first character lowercase.
quotemeta EXPR
Returns EXPR with all regular expression metacharacters quoted.
rindex STR, SUBSTR [ , OFFSET ]
Returns the position of the last SUBSTR in STR at or before OFFSET.
substr EXPR, OFFSET [ , LEN ]
Extracts a substring of length LEN out of EXPR and returns it. If OFFSET is negative, counts from the end of the string. May be assigned to.
Returns an uppercased version of EXPR.
ucfirst EXPR
Returns EXPR with the first character uppercased.

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Array and List Functions

delete $HASH{KEY}
Deletes the specified value from the specified hash. Returns the deleted value unless HASH is tied to a package that does not support this.
each %HASH
Returns a 2-element array consisting of the key and value for the next value of the hash. Entries are returned in an apparently random order. After all values of the hash have been returned, a null array is returned. The next call to each after that will start iterating again.
exists EXPR†
Checks if the specified hash key exists in its hash array.
Evaluates EXPR or BLOCK for each element of the LIST, locally setting $_ to refer to the element. Modifying $_ will modify the corresponding element from LIST. Returns the array of elements from LIST for which EXPR returned true.
Joins the separate strings of LIST into a single string with fields separated by the value of EXPR, and returns the string.
keys %HASH
Returns an array with all of the keys of the named hash.
Evaluates EXPR or BLOCK for each element of the LIST, locally setting $_ to refer to the element. Modifying $_ will modify the corresponding element from LIST. Returns the list of results.
pop @ARRAY
Pops off and returns the last value of the array.
Pushes the values of LIST onto the end of the array.
reverse LIST
In array context, returns the LIST in reverse order. In scalar context: returns the first element of LIST with bytes reversed.
scalar @ARRAY
Returns the number of elements in the array.
scalar %HASH
Returns a true value if the hash has elements defined.
shift [ @ARRAY ]
Shifts the first value of the array off and returns it, shortening the array by 1 and moving everything down. If @ARRAY is omitted, shifts @ARGV in main and @_ in subroutines.
Sorts the LIST and returns the sorted array value. SUBROUTINE, if specified, must return less than zero, zero, or greater than zero, depending on how the elements of the array (available to the routine as $a and $b) are to be ordered. SUBROUTINE may be the name of a user-defined routine, or a BLOCK.
splice @ARRAY, OFFSET [ , LENGTH [ , LIST ] ]
Removes the elements of @ARRAY designated by OFFSET and LENGTH, and replaces them with LIST (if specified). Returns the elements removed.
split [ PATTERN [ , EXPR† [ , LIMIT ] ] ]
Splits a string into an array of strings, and returns it. If LIMIT is specified, splits into at most that number of fields. If PATTERN is also omitted, splits at the whitespace. If not in array context, returns number of fields and splits to @_. See also Search and Replace Functions.
unshift @ARRAY, LIST
Prepends list to the front of the array, and returns the number of elements in the new array.
values %HASH
Returns a normal array consisting of all the values of the named hash.

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Regular Expressions

Each character matches itself, unless it is one of the special characters + ? . * ^ $ ( ) [ ] { } | \. The special meaning of these characters can be escaped using a \.

. matches an arbitrary character, but not a newline unless it is a single-line match (see m//s).
(...) groups a series of pattern elements to a single element.
^ matches the beginning of the target. In multiline mode (see m//m) also matches after every newline character.
$ matches the end of the line. In multiline mode also matches before every newline character.
[ ... ] denotes a class of characters to match. [^ ... ] negates the class.
( ... | ... | ... ) matches one of the alternatives.
(?# TEXT ) Comment.
(?: REGEXP ) Like (REGEXP) but does not make back-references.
(?= REGEXP ) Zero width positive look-ahead assertion.
(?! REGEXP ) Zero width negative look-ahead assertion.
(? MODIFIER ) Embedded pattern-match modifier. MODIFIER can be one or more of i, m, s, or x.

Quantified subpatterns match as many times as possible. When followed with a ? they match the minimum number of times. These are the quantifiers:

+ matches the preceding pattern element one or more times.
? matches zero or one times.
* matches zero or more times.
{N,M} denotes the minimum N and maximum M match count. {N} means exactly N times; {N,} means at least N times.

A \ escapes any special meaning of the following character if non-alphanumeric, but it turns most alphanumeric characters into something special:

\w matches alphanumeric, including _, \W matches non-alphanumeric.
\s matches whitespace, \S matches non-whitespace.
\d matches numeric, \D matches non-numeric.
\A matches the beginning of the string, \Z matches the end.
\b matches word boundaries, \B matches non-boundaries.
\G matches where the previous m//g search left off.
\n, \r, \f, \t etc. have their usual meaning.
\w, \s and \d may be used within character classes, \b denotes backspace in this context.


\1 ... \9 refer to matched subexpressions, grouped with (), inside the match.
\10 and up can also be used if the pattern matches that many subexpressions.

See also $1 ... $9, $+, $&, $`, and $' in section Special Variables.

With modifier x, whitespace can be used in the patterns for readability purposes.

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Search and Replace Functions

[ EXPR =~ ] [ m ] /PATTERN/ [ g ] [ i ] [ m ] [ o ] [ s ] [ x ]
Searches EXPR (default: $_) for a pattern. If you prepend an m you can use almost any pair of delimiters instead of the slashes. If used in array context, an array is returned consisting of the subexpressions matched by the parentheses in the pattern, i.e., ($1,$2,$3,...).
Optional modifiers: g matches as many times as possible; i searches in a case-insensitive manner; o interpolates variables only once. m treats the string as multiple lines; s treats the string as a single line; x allows for regular expression extensions.
If PATTERN is empty, the most recent pattern from a previous match or replacement is used.
With g the match can be used as an iterator in scalar context.
This is just like the /PATTERN/ search, except that it matches only once between calls to the reset operator.
[ $VAR =~ ] s/PATTERN/REPLACEMENT/ [ e ] [ g ] [ i ] [ m ] [ o ] [ s ] [ x ]
Searches a string for a pattern, and if found, replaces that pattern with the replacement text. It returns the number of substitutions made, if any; if no substitutions are made, it returns false.
Optional modifiers: g replaces all occurrences of the pattern; e evaluates the replacement string as a Perl expression; for any other modifiers, see /PATTERN/ matching. Almost any delimiter may replace the slashes; if single quotes are used, no interpretation is done on the strings between the delimiters, otherwise the strings are interpolated as if inside double quotes.
If bracketing delimiters are used, PATTERN and REPLACEMENT may have their own delimiters, e.g., s(foo)[bar]. If PATTERN is empty, the most recent pattern from a previous match or replacement is used.
[ $VAR =~ ] tr/SEARCHLIST/REPLACEMENTLIST/ [ c ] [ d ] [ s ]
Translates all occurrences of the characters found in the search list with the corresponding character in the replacement list. It returns the number of characters replaced. y may be used instead of tr.
Optional modifiers: c complements the SEARCHLIST; d deletes all characters found in SEARCHLIST that do not have a corresponding character in REPLACEMENTLIST; s squeezes all sequences of characters that are translated into the same target character into one occurrence of this character.
Returns the position where the last m//g search left off for SCALAR. May be assigned to.
study [ $VAR† ]
Study the scalar variable $VAR in anticipation of performing many pattern matches on its contents before the variable is next modified.

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File Test Operators

These unary operators takes one argument, either a filename or a filehandle, and test the associated file to see if something is true about it. If the argument is omitted, they test $_ (except for -t, which tests STDIN). If the special argument _ (underscore) is passed, they use the information from the preceding test or stat call.

-r -w -x  File is readable/writable/executable by effective uid/gid.
-R -W -X File is readable/writable/executable by real uid/gid.
-o -O File is owned by effective/real uid.
-e -z File exists/has zero size.
-s File exists and has non-zero size. Returns the size.
-f -d File is a plain file/a directory.
-l -S -p File is a symbolic link/a socket/a named pipe (FIFO).
-b -c File is a block/character special file.
-u -g -k File has setuid/setgid/sticky bit set.
-t Tests if filehandle (STDIN by default) is opened to a tty.
-T -B File is a text/non-text (binary) file. -T and -B return true on a null file, or a file at EOF when testing a filehandle.
-M -A -C File modification / access / inode-change time. Measured in days. Value returned reflects the file age at the time the script started. See also $^T in the section Special Variables.

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File Operations

Functions operating on a list of files return the number of files successfully operated upon.
chmod LIST
Changes the permissions of a list of files. The first element of the list must be the numerical mode.
chown LIST
Changes the owner and group of a list of files. The first two elements of the list must be the numerical uid and gid.
truncate FILE, SIZE
Truncates FILE to SIZE. FILE may be a filename or a filehandle.
Creates a new filename linked to the old filename.
lstat FILE
Like stat, but does not traverse a final symbolic link.
mkdir DIR, MODE
Creates a directory with given permissions. Sets $! on failure.
readlink EXPR†
Returns the value of a symbolic link.
Changes the name of a file.
Deletes the directory if it is empty. Sets $! on failure.
stat FILE
Returns a 13-element array (0: $dev, 1: $ino, 2: $mode, 3: $nlink, 4: $uid, 5: $gid, 6: $rdev, 7: $size, 8: $atime, 9: $mtime, 10: $ctime, 11: $blksize, 12: $blocks). FILE can be a filehandle, an expression evaluating to a filename, or _ to refer to the last file test operation or stat call. Returns a null list if the stat fails.
Creates a new filename symbolically linked to the old filename.
unlink LIST
Deletes a list of files.
utime LIST
Changes the access and modification times. The first two elements of the list must be the numerical access and modification times.

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Input / Output

In input/output operations, FILEHANDLE may be a filehandle as opened by the open operator, a predefined filehandle (e.g., STDOUT) or a scalar variable that evaluates to the name of a filehandle to be used.
In scalar context, reads a single line from the file opened on FILEHANDLE. In array context, reads the whole file.
< >
Reads from the input stream formed by the files specified in @ARGV, or standard input if no arguments were supplied.
Arranges for the file opened on FILEHANDLE to be read or written in binary mode as opposed to text mode (null operation on UNIX).
Closes the file or pipe associated with the filehandle.
dbmclose %HASH
Deprecated, use untie instead.
Deprecated, use tie instead.
Returns true if the next read will return end of file, or if the file is not open.
Returns the EOF status for the last file read.
Indicates EOF on the pseudo file formed of the files listed on the command line.
Implements the fcntl(2) function. This function has non-standard return values.
Returns the file descriptor for a given (open) file.
Calls flock(2) on the file. OPERATION formed by adding 1 (shared), 2 (exclusive), 4 (non-blocking), or 8 (unlock).
Yields the next character from the file, or an empty string on end of file. If FILEHANDLE is omitted, reads from STDIN.
Performs ioctl(2) on the file. This function has non-standard return values.
Opens a file and associates it with FILEHANDLE. If FILENAME is omitted, the scalar variable of the same name as the FILEHANDLE must contain the filename.
The following filename conventions apply when opening a file.
"FILE" open FILE for input. Also "<FILE".
">FILE" open FILE for output, creating it if necessary.
">>FILE" open FILE in append mode.
"+<FILE" open FILE with read/write access (file must exist).
"+>FILE" open FILE with read/write access (file truncated).
"|CMD" opens a pipe to command CMD; forks if CMD is -.
"CMD|" opens a pipe from command CMD; forks if CMD is -.
FILE may be &FILEHND in which case the new filehandle is connected to the (previously opened) filehandle FILEHND. If it is &=N, FILE will be connected to the given file descriptor. open returns undef upon failure, true otherwise.
Returns a pair of connected pipes.
print [ FILEHANDLE ] [ LIST† ]
Equivalent to print FILEHANDLE sprintf LIST.
printf[([FILEHANDLE] LIST†)]
Equivalent to print FILEHANDLE sprintf(LIST).
Reads LENGTH binary bytes from the file into the variable at OFFSET. Returns number of bytes actually read.
Arbitarily positions the file. Returns true if successful.
select [ FILEHANDLE ]
Returns the currently selected filehandle. Sets the current default filehandle for output operations if FILEHANDLE is supplied.
Performs a select(2) system call with the same parameters.
sprintf FORMAT, LIST
Returns a string formatted by (almost all of) the usual printf(3) conventions.
Reads LENGTH bytes into $VAR at OFFSET.
Writes LENGTH bytes from SCALAR at OFFSET.
Returns the current file position for the file. If FILENAME is omitted, assumes the file last read.
write [ FILEHANDLE ]
Writes a formatted record to the specified file, using the format associated with that file.

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formline PICTURE, LIST
Formats LIST according to PICTURE and accumulates the result into $^A.
write [ FILEHANDLE ]
Writes a formatted record to the specified file, using the format associated with that file.

Formats are defined as follows:

FORMLIST pictures the lines, and contains the arguments which will give values to the fields in the lines. NAME defaults to STDOUT if omitted.

Picture fields are:

Use ^ instead of @ for multiline block filling.
Use ~ at the beginning of a line to suppress unwanted empty lines.
Use ~~ at the beginning of a line to have this format line repeated until all fields are exhausted.
Use $- to zero to force a page break on the next write.
See also $^, $~, $^A, $^F, $- and $= in section Special Variables.

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Directory Reading Routines

closedir DIRHANDLE
Closes a directory opened by opendir.
Opens a directory on the handle specified.
Returns the next entry (or an array of entries) from the directory.
rewinddir DIRHANDLE
Positions the directory to the beginning.
Sets position for readdir on the directory.
Returns the position in the directory.

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System Interaction

alarm EXPR
Schedules a SIGALRM to be delivered after EXPR seconds.
chdir [ EXPR ]
Changes the working directory. Uses $ENV{"HOME"} or $ENV{"LOGNAME"} if EXPR is omitted.
chroot FILENAME†
Changes the root directory for the process and its children.
die [ LIST ]
Prints the value of LIST to STDERR and exits with the current value of $! (errno). If $! is 0, exits with the value of ($? >> 8). If ($? >> 8) is 0, exits with 255. LIST defaults to "Died".
exec LIST
Executes the system command in LIST; does not return.
exit [ EXPR ]
Exits immediately with the value of EXPR, which defaults to 0 (zero). Calls END routines and object destructors before exiting.
Does a fork(2) system call. Returns the process ID of the child to the parent process and zero to the child process.
Returns the current login name as known by the system.
getpgrp [ PID ]
Returns the process group for process PID (0, or omitted, means the current process).
Returns the process ID of the parent process.
getpriority WHICH, WHO
Returns the current priority for a process, process group, or user.
glob PAT
Returns a list of filenames that match the shell pattern PAT.
kill LIST
Sends a signal to a list of processes. The first element of the list must be the signal to send (either numeric, or its name as a string).
setpgrp PID, PGRP
Sets the process group for the PID (0 means the current process).
setpriority WHICH, WHO, PRIORITY
Sets the current priority for a process, process group, or a user.
sleep [ EXPR ]
Causes the program to sleep for EXPR seconds, or forever if no EXPR. Returns the number of seconds actually slept.
syscall LIST
Calls the system call specified in the first element of the list, passing the rest of the list as arguments to the call.
system LIST
Does exactly the same thing as exec LIST except that a fork is performed first, and the parent process waits for the child process to complete.
Returns a 4-element array (0: $user, 1: $system, 2: $cuser, 3: $csystem) giving the user and system times, in seconds, for this process and the children of this process.
umask [ EXPR ]
Sets the umask for the process and returns the old one. If EXPR is omitted, returns current umask value.
Waits for a child process to terminate and returns the process ID of the deceased process (-1 if none). The status is returned in $?.
waitpid PID, FLAGS
Performs the same function as the corresponding system call.
warn [ LIST ]
Prints the message on STDERR like die, but doesn't exit. LIST defaults to "Warning: something's wrong".

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Accepts a new socket.
Binds the NAME to the SOCKET.
connect SOCKET, NAME
Connects the NAME to the SOCKET.
getpeername SOCKET
Returns the socket address of the other end of the SOCKET.
getsockname SOCKET
Returns the name of the SOCKET.
Returns the socket options.
Starts listening on the specified SOCKET.
Receives a message on SOCKET.
send SOCKET, MSG, FLAGS [ , TO ]
Sends a message on the SOCKET.
Sets the requested socket option.
shutdown SOCKET, HOW
Shuts down a SOCKET.
Creates a SOCKET in DOMAIN with TYPE and PROTOCOL.
Works the same as socket, but creates a pair of bidirectional sockets.

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System V IPC

You need to require "sys/" before you can use the symbolic names of the operations.

msgctl ID, CMD, ARGS
Calls msgctl(2). If CMD is &IPC_STAT then ARGS must be a variable.
msgget KEY, FLAGS
Creates a message queue for KEY. Returns the message queue identifier.
msgsnd ID, MSG, FLAGS
Sends MSG to queue ID.
Receives a message from queue ID into VAR.
Calls semctl(2). If CMD is &IPC_STAT of &GETALL then ARG must be a variable.
Creates a set of semaphores for KEY. Returns the message semaphore identifier.
semop KEY, ...
Performs semaphore operations.
shmctl ID, CMD, ARG
Calls shmctl(2). If CMD is &IPC_STAT then ARG must be a variable.
Creates shared memory. Returns the shared memory segment identifier.
shmread ID, $VAR, POS, SIZE
Reads at most SIZE bytes of the contents of shared memory segment ID starting at offset POS into VAR.
shmwrite ID, STRING, POS, SIZE
Writes at most SIZE bytes of STRING into the contents of shared memory segment ID at offset POS.

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defined EXPR
Tests whether the lvalue EXPR has an actual value.
Executes FILENAME as a Perl script. See also require in the section Subroutines, Packages and Modules.
dump [ LABEL ]
Immediate core dump. When reincarnated, starts at LABEL.
eval { EXPR ; ... }
Executes the code between { and }. Traps runtime errors as described with eval(EXPR), in the section String Functions.
local ( LIST )
Creates a scope for the listed variables local to the enclosing block, subroutine or eval.
my ( LIST )
Creates a scope for the listed variables lexically local to the enclosing block, subroutine or eval.
ref EXPR†
Returns a true value if EXPR is a reference. Returns the package name if EXPR has been blessed into a package.
reset [ EXPR ]
Resets ?? searches so that they work again. EXPR is a list of single letters. All variables and arrays beginning with one of those letters are reset to their pristine state. Only affects the current package.
scalar EXPR
Forces evaluation of EXPR in scalar context.
undef [ LVALUE ]
Undefines the LVALUE. Always returns the undefined value.
Returns true if the current context expects an array value.

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Information from System Files

• passwd
Returns ($name, $passwd, $uid, $gid, $quota, $comment, $gcos, $dir, $shell).
endpwent Ends lookup processing.
getpwent Gets next user information.
getpwnam NAME Gets information by name.
getpwuid UID Gets information by user ID.
setpwent Resets lookup processing.
• group
Returns ($name, $passwd, $gid, $members).
endgrent Ends lookup processing.
getgrgid GID Gets information by group ID.
getgrnam NAME Gets information by name.
getgrent Gets next information.
setgrent Resets lookup processing.
• hosts
Returns ($name, $aliases, $addrtype, $length, @addrs).
endhostent Ends lookup processing.
gethostbyaddr ADDR, ADDRTYPE Gets information by IP address.
gethostbyname NAME Gets information by hostname.
gethostent Gets next host information.
sethostent STAYOPEN Resets lookup processing.
• networks
Returns ($name, $aliases, $addrtype, $net).
endnetent Ends lookup processing.
getnetbyaddr ADDR, TYPE Gets information by address and type.
getnetbyname NAME Gets information by network name.
getnetent Gets next network information.
setnetent STAYOPEN Resets lookup processing.
• services
Returns ($name, $aliases, $port, $proto).
endservent Ends lookup processing.
getservbyname NAME, PROTO Gets information by service name.
getservbyport PORT, PROTO Gets information by service port.
getservent Gets next service information.
setservent STAYOPEN Resets lookup processing.
• protocols
Returns ($name, $aliases, $proto).
endprotoent Ends lookup processing.
getprotobyname NAME Gets information by protocol name.
getprotobynumber NUMBER Gets information by protocol number.
getprotoent Gets next protocol information.
setprotoent STAYOPEN Resets lookup processing.

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Special Variables

The following variables are global and should be localized in subroutines:
$_ The default input and pattern-searching space.
$. The current input line number of the last filehandle that was read.
$/ The input record separator, newline by default. May be multicharacter.
$, The output field separator for the print operator.
$" The separator that joins elements of arrays interpolated in strings.
$\ The output record separator for the print operator.
$# The output format for printed numbers. Deprecated.
$* Set to 1 to do multiline matching within strings. Deprecated, see the m and s modifiers in section Search and Replace Functions.
$? The status returned by the last `...` command, pipe close or system operator.
$] The perl version number, e.g., 5.001.
$[ The index of the first element in an array, and of the first character in a substring. Default is 0. Deprecated.
$; The subscript separator for multidimensional array emulation. Default is "\034".
$! If used in a numeric context, yields the current value of errno. If used in a string context, yields the corresponding error string.
$@ The Perl error message from the last eval or do EXPR command.
$: The set of characters after which a string may be broken to fill continuation fields (starting with ^) in a format.
$0 The name of the file containing the Perl script being executed. May be assigned to.
$$ The process ID of the currently executing Perl program. Altered (in the child process) by fork.
$< The real user ID of this process.
$> The effective user ID of this process.
$( The real group ID of this process.
$) The effective group ID of this process.
$^A The accumulator for formline and write operations.
$^D The debug flags as passed to perl using -D.
$^F The highest system file descriptor, ordinarily 2.
$^I In-place edit extension as passed to Perl using -i.
$^L Formfeed character used in formats.
$^P Internal debugging flag.
$^T The time (as delivered by time) when the program started. This value is used by the file test operators -M, -A and -C.
$^W The value of the -w option as passed to Perl.
$^X The name by which the currently executing program was invoked.
The following variables are context dependent and need not be localized:
$% The current page number of the currently selected output channel.
$= The page length of the current output channel. Default is 60 lines.
$- The number of lines remaining on the page.
$~ The name of the current report format.
$^ The name of the current top-of-page format.
$| If set to nonzero, forces a flush after every write or print on the currently selected output channel. Default is 0.
$ARGV The name of the current file when reading from <>.
The following variables are always local to the current block:
$& The string matched by the last successful pattern match.
$` The string preceding what was matched by the last successful match.
$' The string following what was matched by the last successful match.
$+ The last bracket matched by the last search pattern.
$1...$9...   Contain the subpatterns from the corresponding sets of parentheses in the last pattern successfully matched. $10... and up are only available if the match contained that many subpatterns.

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Special Arrays

@ARGV Contains the command-line arguments for the script (not including the command name).
@EXPORT Names the methods a package exports by default.
@EXPORT_OK  Names the methods a package can export upon explicit request.
@INC Contains the list of places to look for Perl scripts to be evaluated by the do FILENAME and require commands.
@ISA List of base classes of a package.
@_ Parameter array for subroutines. Also used by split if not in array context.
%ENV Contains the current environment.
%INC List of files that have been included with require or do.
%OVERLOAD Can be used to overload operators in a package.
%SIG Used to set signal handlers for various signals.

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Environment Variables

Perl uses the following environment variables.

HOME Used if chdir has no argument.
LOGDIR Used if chdir has no argument and HOME is not set.
PATH Used in executing subprocesses, and in finding the Perl script if -S is used.
PERL5LIB  A colon-separated list of directories to look in for Perl library files before looking in the standard library and the current directory.
PERL5DB The command to get the debugger code.
Defaults to BEGIN { require '' }.
PERLLIB Used instead of PERL5LIB if the latter is not defined.

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The Perl Debugger

The Perl symbolic debugger is invoked with perl -d.
h Prints out a help message.
T Prints a stack trace.
s Single steps.
n Single steps around subroutine call.
RETURN key Repeats last s or n.
r Returns from the current subroutine.
c [ LINE ] Continues (until LINE, or another breakpoint, or exit).
p EXPR Prints EXPR.
l [ RANGE ] Lists a range of lines. RANGE may be a number, start-end, start+amount, or a subroutine name. If RANGE is omitted, lists next window.
w Lists window around current line.
- Lists previous window.
f FILE Switches to FILE and starts listing it.
l SUB Lists the named subroutine.
S List the names of all subroutines.
/PATTERN/ Searches forward for PATTERN.
?PATTERN? Searches backward for PATTERN.
b [ LINE [ CONDITION ] ]   Sets breakpoint at LINE; default is the current line.
b SUB [ CONDITION ] Sets breakpoint at the subroutine.
d [ LINE ] Deletes breakpoint at the given line.
D Deletes all breakpoints.
L Lists lines that have breakpoints or actions.
a LINE COMMAND Sets an action for line.
A Deletes all line actions.
< COMMAND Sets an action to be executed before every debugger prompt.
> COMMAND Sets an action to be executed before every s, c or n command.
V [ PACKAGE [ VARS ] ]   Lists all variables in a package. Default package is main.
X [ VARS ] Like V, but assumes current package.
! [ [-]NUMBER ] Re-executes a command. Default is the previous command.
H [ -NUMBER ] Displays the last -NUMBER commands of more than one letter.
t Toggles trace mode.
= [ ALIAS VALUE ] Sets alias, or lists current aliases.
q Quits. You may also use your EOF key character.
COMMAND Executes COMMAND as a Perl statement.

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Other Summaries and Demos

You are visitor [Odometer] since 3 August 1996

Sorry, but I do not have time to provide free answers to questions about Perl.
(I'm busy trying to make a living!) So please don't e-mail your questions to me.

Text copyright © 1996 Johan Vromans
HTML copyright © 1996-2010 Rex Swain
Email, Web
Reports of errors or omissions appreciated