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arguments.

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 LIST 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 LIST.

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 I<looks> like a function, therefore it I<is> 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:

    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.

If you run Perl with the B<-w> switch it can warn you about this.  For
example, the third line above produces:

    print (...) interpreted as function at - line 1.
    Useless use of integer addition in void context at - line 1.

A few functions take no arguments at all, and therefore work as neither
unary nor list operators.  These include such functions as C<time>
and C<endpwent>.  For example, C<time+86_400> always means
C<time() + 86_400>.

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.

Remember the following important rule: There is B<no rule> 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.

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 C<(1,2,3)> 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.

In general, functions in Perl that serve as wrappers for system calls
of the same name (like chown(2), fork(2), closedir(2), etc.) all return
true when they succeed and C<undef> otherwise, as is usually mentioned
in the descriptions below.  This is different from the C interfaces,
which return C<-1> on failure.  Exceptions to this rule are C<wait>,
C<waitpid>, and C<syscall>.  System calls also set the special C<$!>
variable on failure.  Other functions do not, except accidentally.

=head2 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.

=over 4

=item Functions for SCALARs or strings

C<chomp>, C<chop>, C<chr>, C<crypt>, C<hex>, C<index>, C<lc>, C<lcfirst>,
C<length>, C<oct>, C<ord>, C<pack>, C<q/STRING/>, C<qq/STRING/>, C<reverse>,
C<rindex>, C<sprintf>, C<substr>, C<tr///>, C<uc>, C<ucfirst>, C<y///>

=item Regular expressions and pattern matching

C<m//>, C<pos>, C<quotemeta>, C<s///>, C<split>, C<study>, C<qr//>

=item Numeric functions

C<abs>, C<atan2>, C<cos>, C<exp>, C<hex>, C<int>, C<log>, C<oct>, C<rand>,
C<sin>, C<sqrt>, C<srand>

=item Functions for real @ARRAYs

C<pop>, C<push>, C<shift>, C<splice>, C<unshift>

=item Functions for list data

C<grep>, C<join>, C<map>, C<qw/STRING/>, C<reverse>, C<sort>, C<unpack>

=item Functions for real %HASHes

C<delete>, C<each>, C<exists>, C<keys>, C<values>

=item Input and output functions

C<binmode>, C<close>, C<closedir>, C<dbmclose>, C<dbmopen>, C<die>, C<eof>,
C<fileno>, C<flock>, C<format>, C<getc>, C<print>, C<printf>, C<read>,
C<readdir>, C<rewinddir>, C<seek>, C<seekdir>, C<select>, C<syscall>,
C<sysread>, C<sysseek>, C<syswrite>, C<tell>, C<telldir>, C<truncate>,
C<warn>, C<write>

=item Functions for fixed length data or records

C<pack>, C<read>, C<syscall>, C<sysread>, C<syswrite>, C<unpack>, C<vec>

=item Functions for filehandles, files, or directories

C<-I<X>>, C<chdir>, C<chmod>, C<chown>, C<chroot>, C<fcntl>, C<glob>,
C<ioctl>, C<link>, C<lstat>, C<mkdir>, C<open>, C<opendir>,
C<readlink>, C<rename>, C<rmdir>, C<stat>, C<symlink>, C<sysopen>,
C<umask>, C<unlink>, C<utime>

=item Keywords related to the control flow of your Perl program

C<caller>, C<continue>, C<die>, C<do>, C<dump>, C<eval>, C<exit>,
C<goto>, C<last>, C<next>, C<redo>, C<return>, C<sub>, C<wantarray>

=item Keywords related to scoping

C<caller>, C<import>, C<local>, C<my>, C<our>, C<package>, C<use>

=item Miscellaneous functions

C<defined>, C<dump>, C<eval>, C<formline>, C<local>, C<my>, C<our>, C<reset>,
C<scalar>, C<undef>, C<wantarray>

=item Functions for processes and process groups

C<alarm>, C<exec>, C<fork>, C<getpgrp>, C<getppid>, C<getpriority>, C<kill>,
C<pipe>, C<qx/STRING/>, C<setpgrp>, C<setpriority>, C<sleep>, C<system>,
C<times>, C<wait>, C<waitpid>

=item Keywords related to perl modules

C<do>, C<import>, C<no>, C<package>, C<require>, C<use>

=item Keywords related to classes and object-orientedness

C<bless>, C<dbmclose>, C<dbmopen>, C<package>, C<ref>, C<tie>, C<tied>,
C<untie>, C<use>

=item Low-level socket functions

C<accept>, C<bind>, C<connect>, C<getpeername>, C<getsockname>,
C<getsockopt>, C<listen>, C<recv>, C<send>, C<setsockopt>, C<shutdown>,
C<socket>, C<socketpair>

=item System V interprocess communication functions

C<msgctl>, C<msgget>, C<msgrcv>, C<msgsnd>, C<semctl>, C<semget>, C<semop>,
C<shmctl>, C<shmget>, C<shmread>, C<shmwrite>

=item Fetching user and group info

C<endgrent>, C<endhostent>, C<endnetent>, C<endpwent>, C<getgrent>,
C<getgrgid>, C<getgrnam>, C<getlogin>, C<getpwent>, C<getpwnam>,
C<getpwuid>, C<setgrent>, C<setpwent>

=item Fetching network info

C<endprotoent>, C<endservent>, C<gethostbyaddr>, C<gethostbyname>,
C<gethostent>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>,
C<getprotobyname>, C<getprotobynumber>, C<getprotoent>,
C<getservbyname>, C<getservbyport>, C<getservent>, C<sethostent>,
C<setnetent>, C<setprotoent>, C<setservent>

=item Time-related functions

C<gmtime>, C<localtime>, C<time>, C<times>

=item Functions new in perl5

C<abs>, C<bless>, C<chomp>, C<chr>, C<exists>, C<formline>, C<glob>,
C<import>, C<lc>, C<lcfirst>, C<map>, C<my>, C<no>, C<our>, C<prototype>,
C<qx>, C<qw>, C<readline>, C<readpipe>, C<ref>, C<sub*>, C<sysopen>, C<tie>,
C<tied>, C<uc>, C<ucfirst>, C<untie>, C<use>

* - C<sub> was a keyword in perl4, but in perl5 it is an
operator, which can be used in expressions.

=item Functions obsoleted in perl5

C<dbmclose>, C<dbmopen>

=back

=head2 Portability

Perl was born in Unix and can therefore access all common Unix
system calls.  In non-Unix environments, the functionality of some
Unix system calls may not be available, or details of the available
functionality may differ slightly.  The Perl functions affected
by this are:

C<-X>, C<binmode>, C<chmod>, C<chown>, C<chroot>, C<crypt>,
C<dbmclose>, C<dbmopen>, C<dump>, C<endgrent>, C<endhostent>,
C<endnetent>, C<endprotoent>, C<endpwent>, C<endservent>, C<exec>,
C<fcntl>, C<flock>, C<fork>, C<getgrent>, C<getgrgid>, C<gethostbyname>,
C<gethostent>, C<getlogin>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>,
C<getppid>, C<getpgrp>, C<getpriority>, C<getprotobynumber>,
C<getprotoent>, C<getpwent>, C<getpwnam>, C<getpwuid>,
C<getservbyport>, C<getservent>, C<getsockopt>, C<glob>, C<ioctl>,
C<kill>, C<link>, C<lstat>, C<msgctl>, C<msgget>, C<msgrcv>,
C<msgsnd>, C<open>, C<pipe>, C<readlink>, C<rename>, C<select>, C<semctl>,
C<semget>, C<semop>, C<setgrent>, C<sethostent>, C<setnetent>,
C<setpgrp>, C<setpriority>, C<setprotoent>, C<setpwent>,
C<setservent>, C<setsockopt>, C<shmctl>, C<shmget>, C<shmread>,
C<shmwrite>, C<socket>, C<socketpair>,
C<stat>, C<symlink>, C<syscall>, C<sysopen>, C<system>,
C<times>, C<truncate>, C<umask>, C<unlink>,
C<utime>, C<wait>, C<waitpid>

For more information about the portability of these functions, see
L<perlport> and other available platform-specific documentation.

=head2 Alphabetical Listing of Perl Functions

=over 8

=item -X FILEHANDLE

=item -X EXPR

=item -X

A file test, where X is one of the letters listed below.  This unary
operator takes one argument, either a filename or a filehandle, and
tests the associated file to see if something is true about it.  If the
argument is omitted, tests C<$_>, except for C<-t>, which tests STDIN.
Unless otherwise documented, it returns C<1> for true and C<''> for false, or
the undefined value if the file doesn't exist.  Despite the funny
names, precedence is the same as any other named unary operator, and
the argument may be parenthesized like any other unary operator.  The
operator may be any of:
X<-r>X<-w>X<-x>X<-o>X<-R>X<-W>X<-X>X<-O>X<-e>X<-z>X<-s>X<-f>X<-d>X<-l>X<-p>
X<-S>X<-b>X<-c>X<-t>X<-u>X<-g>X<-k>X<-T>X<-B>X<-M>X<-A>X<-C>

    -r	File is readable by effective uid/gid.
    -w	File is writable by effective uid/gid.
    -x	File is executable by effective uid/gid.
    -o	File is owned by effective uid.

    -R	File is readable by real uid/gid.
    -W	File is writable by real uid/gid.
    -X	File is executable by real uid/gid.
    -O	File is owned by real uid.

    -e	File exists.
    -z	File has zero size (is empty).
    -s	File has nonzero size (returns size in bytes).

    -f	File is a plain file.
    -d	File is a directory.
    -l	File is a symbolic link.
    -p	File is a named pipe (FIFO), or Filehandle is a pipe.

benchmarks/app/perlfunc.pod  view on Meta::CPAN

This safer version of L</chop> removes any trailing string
that corresponds to the current value of C<$/> (also known as
$INPUT_RECORD_SEPARATOR in the C<English> module).  It returns the total
number of characters removed from all its arguments.  It's often used to
remove the newline from the end of an input record when you're worried
that the final record may be missing its newline.  When in paragraph
mode (C<$/ = "">), it removes all trailing newlines from the string.
When in slurp mode (C<$/ = undef>) or fixed-length record mode (C<$/> is
a reference to an integer or the like, see L<perlvar>) chomp() won't
remove anything.
If VARIABLE is omitted, it chomps C<$_>.  Example:

    while (<>) {
	chomp;	# avoid \n on last field
	@array = split(/:/);
	# ...
    }

If VARIABLE is a hash, it chomps the hash's values, but not its keys.

You can actually chomp anything that's an lvalue, including an assignment:

    chomp($cwd = `pwd`);
    chomp($answer = <STDIN>);

If you chomp a list, each element is chomped, and the total number of
characters removed is returned.

If the C<encoding> pragma is in scope then the lengths returned are
calculated from the length of C<$/> in Unicode characters, which is not
always the same as the length of C<$/> in the native encoding.

Note that parentheses are necessary when you're chomping anything
that is not a simple variable.  This is because C<chomp $cwd = `pwd`;>
is interpreted as C<(chomp $cwd) = `pwd`;>, rather than as
C<chomp( $cwd = `pwd` )> which you might expect.  Similarly,
C<chomp $a, $b> is interpreted as C<chomp($a), $b> rather than
as C<chomp($a, $b)>.

=item chop VARIABLE

=item chop( LIST )

=item chop

Chops off the last character of a string and returns the character
chopped.  It is much more efficient than C<s/.$//s> because it neither
scans nor copies the string.  If VARIABLE is omitted, chops C<$_>.
If VARIABLE is a hash, it chops the hash's values, but not its keys.

You can actually chop anything that's an lvalue, including an assignment.

If you chop a list, each element is chopped.  Only the value of the
last C<chop> is returned.

Note that C<chop> returns the last character.  To return all but the last
character, use C<substr($string, 0, -1)>.

See also L</chomp>.

=item chown LIST

Changes the owner (and group) of a list of files.  The first two
elements of the list must be the I<numeric> uid and gid, in that
order.  A value of -1 in either position is interpreted by most
systems to leave that value unchanged.  Returns the number of files
successfully changed.

    $cnt = chown $uid, $gid, 'foo', 'bar';
    chown $uid, $gid, @filenames;

On systems that support fchown, you might pass file handles among the
files.  On systems that don't support fchown, passing file handles
produces a fatal error at run time.

Here's an example that looks up nonnumeric uids in the passwd file:

    print "User: ";
    chomp($user = <STDIN>);
    print "Files: ";
    chomp($pattern = <STDIN>);

    ($login,$pass,$uid,$gid) = getpwnam($user)
	or die "$user not in passwd file";

    @ary = glob($pattern);	# expand filenames
    chown $uid, $gid, @ary;

On most systems, you are not allowed to change the ownership of the
file unless you're the superuser, although you should be able to change
the group to any of your secondary groups.  On insecure systems, these
restrictions may be relaxed, but this is not a portable assumption.
On POSIX systems, you can detect this condition this way:

    use POSIX qw(sysconf _PC_CHOWN_RESTRICTED);
    $can_chown_giveaway = not sysconf(_PC_CHOWN_RESTRICTED);

=item chr NUMBER

=item chr

Returns the character represented by that NUMBER in the character set.
For example, C<chr(65)> is C<"A"> in either ASCII or Unicode, and
chr(0x263a) is a Unicode smiley face.  Note that characters from 128
to 255 (inclusive) are by default not encoded in UTF-8 Unicode for
backward compatibility reasons (but see L<encoding>).

If NUMBER is omitted, uses C<$_>.

For the reverse, use L</ord>.

Note that under the C<bytes> pragma the NUMBER is masked to
the low eight bits.

See L<perlunicode> and L<encoding> for more about Unicode.

=item chroot FILENAME

=item chroot

This function works like the system call by the same name: it makes the
named directory the new root directory for all further pathnames that
begin with a C</> by your process and all its children.  (It doesn't
change your current working directory, which is unaffected.)  For security
reasons, this call is restricted to the superuser.  If FILENAME is
omitted, does a C<chroot> to C<$_>.

=item close FILEHANDLE

=item close

Closes the file or pipe associated with the file handle, returning
true only if IO buffers are successfully flushed and closes the system
file descriptor.  Closes the currently selected filehandle if the
argument is omitted.

You don't have to close FILEHANDLE if you are immediately going to do
another C<open> on it, because C<open> will close it for you.  (See
C<open>.)  However, an explicit C<close> on an input file resets the line
counter (C<$.>), while the implicit close done by C<open> does not.

If the file handle came from a piped open, C<close> will additionally
return false if one of the other system calls involved fails, or if the
program exits with non-zero status.  (If the only problem was that the
program exited non-zero, C<$!> will be set to C<0>.)  Closing a pipe
also waits for the process executing on the pipe to complete, in case you
want to look at the output of the pipe afterwards, and
implicitly puts the exit status value of that command into C<$?>.

Prematurely closing the read end of a pipe (i.e. before the process
writing to it at the other end has closed it) will result in a
SIGPIPE being delivered to the writer.  If the other end can't
handle that, be sure to read all the data before closing the pipe.

Example: