perlfunc.1

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.\" ========================================================================
.\"
.IX Title "PERLFUNC 1"
.TH PERLFUNC 1 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
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.SH "NAME"
perlfunc \- Perl builtin functions
.IX Xref "function"
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The functions in this section can serve as terms in an expression.
They fall into two major categories: list operators and named unary
operators.  These differ in their precedence relationship with a
following comma.  (See the precedence table in perlop.)  List
operators take more than one argument, while unary operators can never
take more than one argument.  Thus, a comma terminates the argument of
a unary operator, but merely separates the arguments of a list
operator.  A unary operator generally provides a scalar context to its
argument, while a list operator may provide either scalar or list
contexts for its arguments.  If it does both, the scalar arguments will
be first, and the list argument will follow.  (Note that there can ever
be only one such list argument.)  For instance, \fIsplice()\fR has three scalar
arguments followed by a list, whereas \fIgethostbyname()\fR has four scalar
arguments.
.PP
In the syntax descriptions that follow, list operators that expect a
list (and provide list context for the elements of the list) are shown
with \s-1LIST\s0 as an argument.  Such a list may consist of any combination
of scalar arguments or list values; the list values will be included
in the list as if each individual element were interpolated at that
point in the list, forming a longer single-dimensional list value.
Commas should separate elements of the \s-1LIST\s0.
.PP
Any function in the list below may be used either with or without
parentheses around its arguments.  (The syntax descriptions omit the
parentheses.)  If you use the parentheses, the simple (but occasionally
surprising) rule is this: It \fIlooks\fR like a function, therefore it \fIis\fR a
function, and precedence doesn't matter.  Otherwise it's a list
operator or unary operator, and precedence does matter.  And whitespace
between the function and left parenthesis doesn't count\*(--so you need to
be careful sometimes:
.PP
.Vb 5
\&    print 1+2+4;        # Prints 7.
\&    print(1+2) + 4;     # Prints 3.
\&    print (1+2)+4;      # Also prints 3!
\&    print +(1+2)+4;     # Prints 7.
\&    print ((1+2)+4);    # Prints 7.
.Ve
.PP
If you run Perl with the \fB\-w\fR switch it can warn you about this.  For
example, the third line above produces:
.PP
.Vb 2
\&    print (...) interpreted as function at \- line 1.
\&    Useless use of integer addition in void context at \- line 1.
.Ve
.PP
A few functions take no arguments at all, and therefore work as neither
unary nor list operators.  These include such functions as \f(CW\*(C`time\*(C'\fR
and \f(CW\*(C`endpwent\*(C'\fR.  For example, \f(CW\*(C`time+86_400\*(C'\fR always means
\&\f(CW\*(C`time() + 86_400\*(C'\fR.
.PP
For functions that can be used in either a scalar or list context,
nonabortive failure is generally indicated in a scalar context by
returning the undefined value, and in a list context by returning the
null list.
.PP
Remember the following important rule: There is \fBno rule\fR that relates
the behavior of an expression in list context to its behavior in scalar
context, or vice versa.  It might do two totally different things.
Each operator and function decides which sort of value it would be most
appropriate to return in scalar context.  Some operators return the
length of the list that would have been returned in list context.  Some
operators return the first value in the list.  Some operators return the
last value in the list.  Some operators return a count of successful
operations.  In general, they do what you want, unless you want
consistency.
.IX Xref "context"
.PP
A named array in scalar context is quite different from what would at
first glance appear to be a list in scalar context.  You can't get a list
like \f(CW\*(C`(1,2,3)\*(C'\fR into being in scalar context, because the compiler knows
the context at compile time.  It would generate the scalar comma operator
there, not the list construction version of the comma.  That means it
was never a list to start with.
.PP
In general, functions in Perl that serve as wrappers for system calls
of the same name (like \fIchown\fR\|(2), \fIfork\fR\|(2), \fIclosedir\fR\|(2), etc.) all return
true when they succeed and \f(CW\*(C`undef\*(C'\fR otherwise, as is usually mentioned
in the descriptions below.  This is different from the C interfaces,
which return \f(CW\*(C`\-1\*(C'\fR on failure.  Exceptions to this rule are \f(CW\*(C`wait\*(C'\fR,
\&\f(CW\*(C`waitpid\*(C'\fR, and \f(CW\*(C`syscall\*(C'\fR.  System calls also set the special \f(CW$!\fR
variable on failure.  Other functions do not, except accidentally.
.Sh "Perl Functions by Category"
.IX Xref "function"
.IX Subsection "Perl Functions by Category"
Here are Perl's functions (including things that look like
functions, like some keywords and named operators)
arranged by category.  Some functions appear in more
than one place.
.IP "Functions for SCALARs or strings" 4
.IX Xref "scalar string character"
.IX Item "Functions for SCALARs or strings"
\&\f(CW\*(C`chomp\*(C'\fR, \f(CW\*(C`chop\*(C'\fR, \f(CW\*(C`chr\*(C'\fR, \f(CW\*(C`crypt\*(C'\fR, \f(CW\*(C`hex\*(C'\fR, \f(CW\*(C`index\*(C'\fR, \f(CW\*(C`lc\*(C'\fR, \f(CW\*(C`lcfirst\*(C'\fR,
\&\f(CW\*(C`length\*(C'\fR, \f(CW\*(C`oct\*(C'\fR, \f(CW\*(C`ord\*(C'\fR, \f(CW\*(C`pack\*(C'\fR, \f(CW\*(C`q//\*(C'\fR, \f(CW\*(C`qq//\*(C'\fR, \f(CW\*(C`reverse\*(C'\fR,
\&\f(CW\*(C`rindex\*(C'\fR, \f(CW\*(C`sprintf\*(C'\fR, \f(CW\*(C`substr\*(C'\fR, \f(CW\*(C`tr///\*(C'\fR, \f(CW\*(C`uc\*(C'\fR, \f(CW\*(C`ucfirst\*(C'\fR, \f(CW\*(C`y///\*(C'\fR
.IP "Regular expressions and pattern matching" 4
.IX Xref "regular expression regex regexp"
.IX Item "Regular expressions and pattern matching"
\&\f(CW\*(C`m//\*(C'\fR, \f(CW\*(C`pos\*(C'\fR, \f(CW\*(C`quotemeta\*(C'\fR, \f(CW\*(C`s///\*(C'\fR, \f(CW\*(C`split\*(C'\fR, \f(CW\*(C`study\*(C'\fR, \f(CW\*(C`qr//\*(C'\fR
.IP "Numeric functions" 4
.IX Xref "numeric number trigonometric trigonometry"
.IX Item "Numeric functions"
\&\f(CW\*(C`abs\*(C'\fR, \f(CW\*(C`atan2\*(C'\fR, \f(CW\*(C`cos\*(C'\fR, \f(CW\*(C`exp\*(C'\fR, \f(CW\*(C`hex\*(C'\fR, \f(CW\*(C`int\*(C'\fR, \f(CW\*(C`log\*(C'\fR, \f(CW\*(C`oct\*(C'\fR, \f(CW\*(C`rand\*(C'\fR,
\&\f(CW\*(C`sin\*(C'\fR, \f(CW\*(C`sqrt\*(C'\fR, \f(CW\*(C`srand\*(C'\fR
.ie n .IP "Functions for real @ARRAYs" 4
.el .IP "Functions for real \f(CW@ARRAYs\fR" 4
.IX Xref "array"
.IX Item "Functions for real @ARRAYs"
\&\f(CW\*(C`pop\*(C'\fR, \f(CW\*(C`push\*(C'\fR, \f(CW\*(C`shift\*(C'\fR, \f(CW\*(C`splice\*(C'\fR, \f(CW\*(C`unshift\*(C'\fR
.IP "Functions for list data" 4
.IX Xref "list"
.IX Item "Functions for list data"
\&\f(CW\*(C`grep\*(C'\fR, \f(CW\*(C`join\*(C'\fR, \f(CW\*(C`map\*(C'\fR, \f(CW\*(C`qw//\*(C'\fR, \f(CW\*(C`reverse\*(C'\fR, \f(CW\*(C`sort\*(C'\fR, \f(CW\*(C`unpack\*(C'\fR
.ie n .IP "Functions for real %HASHes" 4
.el .IP "Functions for real \f(CW%HASHes\fR" 4
.IX Xref "hash"
.IX Item "Functions for real %HASHes"
\&\f(CW\*(C`delete\*(C'\fR, \f(CW\*(C`each\*(C'\fR, \f(CW\*(C`exists\*(C'\fR, \f(CW\*(C`keys\*(C'\fR, \f(CW\*(C`values\*(C'\fR
.IP "Input and output functions" 4
.IX Xref "I O input output dbm"
.IX Item "Input and output functions"