sub tan { sin($_[0]) / cos($_[0]) }
-Note that atan2(0, 0) is not well-defined, however the Perl
-implmentation returns C<0> for this value.
+The return value for C<atan2(0,0)> is implementation-defined; consult
+your atan2(3) manpage for more information.
=item bind SOCKET,NAME
X<bind>
If LAYER is present it is a single string, but may contain multiple
directives. The directives alter the behaviour of the file handle.
-When LAYER is present using binmode on text file makes sense.
+When LAYER is present using binmode on a text file makes sense.
If LAYER is omitted or specified as C<:raw> the filehandle is made
suitable for passing binary data. This includes turning off possible CRLF
Creates a digest string exactly like the crypt(3) function in the C
library (assuming that you actually have a version there that has not
-been extirpated as a potential munitions).
+been extirpated as a potential munition).
crypt() is a one-way hash function. The PLAINTEXT and SALT is turned
into a short string, called a digest, which is returned. The same
Traditionally the result is a string of 13 bytes: two first bytes of
the salt, followed by 11 bytes from the set C<[./0-9A-Za-z]>, and only
-the first eight bytes of the digest string mattered, but alternative
+the first eight bytes of PLAINTEXT mattered. But alternative
hashing schemes (like MD5), higher level security schemes (like C2),
and implementations on non-UNIX platforms may produce different
strings.
delete $ref->[$x][$y][$index];
delete @{$ref->[$x][$y]}[$index1, $index2, @moreindices];
+The C<delete local EXPR> construct can also be used to localize the deletion
+of array/hash elements to the current block.
+See L<perlsub/"Localized deletion of elements of composite types">.
+
=item die LIST
X<die> X<throw> X<exception> X<raise> X<$@> X<abort>
determined.
If there is a syntax error or runtime error, or a C<die> statement is
-executed, an undefined value is returned by C<eval>, and C<$@> is set to the
+executed, C<eval> returns an undefined value in scalar context
+or an empty list in list context, and C<$@> is set to the
error message. If there was no error, C<$@> is guaranteed to be a null
string. Beware that using C<eval> neither silences perl from printing
warnings to STDERR, nor does it stuff the text of warning messages into C<$@>.
is implemented. It is also Perl's exception trapping mechanism, where
the die operator is used to raise exceptions.
+If you want to trap errors when loading an XS module, some problems with
+the binary interface (such as Perl version skew) may be fatal even with
+C<eval> unless C<$ENV{PERL_DL_NONLAZY}> is set. See L<perlrun>.
+
If the code to be executed doesn't vary, you may use the eval-BLOCK
form to trap run-time errors without incurring the penalty of
recompiling each time. The error, if any, is still returned in C<$@>.
Given an expression that specifies a hash element or array element,
returns true if the specified element in the hash or array has ever
-been initialized, even if the corresponding value is undefined. The
-element is not autovivified if it doesn't exist.
+been initialized, even if the corresponding value is undefined.
print "Exists\n" if exists $hash{$key};
print "Defined\n" if defined $hash{$key};
Here's a mailbox appender for BSD systems.
- use Fcntl ':flock'; # import LOCK_* constants
+ use Fcntl qw(:flock SEEK_END); # import LOCK_* and SEEK_END constants
sub lock {
- flock(MBOX,LOCK_EX);
- # and, in case someone appended
- # while we were waiting...
- seek(MBOX, 0, 2);
+ my ($fh) = @_;
+ flock($fh, LOCK_EX) or die "Cannot lock mailbox - $!\n";
+
+ # and, in case someone appended while we were waiting...
+ seek($fh, 0, SEEK_END) or die "Cannot seek - $!\n";
}
sub unlock {
- flock(MBOX,LOCK_UN);
+ my ($fh) = @_;
+ flock($fh, LOCK_UN) or die "Cannot unlock mailbox - $!\n";
}
open(my $mbox, ">>", "/usr/spool/mail/$ENV{'USER'}")
or die "Can't open mailbox: $!";
- lock();
+ lock($mbox);
print $mbox $msg,"\n\n";
- unlock();
+ unlock($mbox);
On systems that support a real flock(), locks are inherited across fork()
calls, whereas those that must resort to the more capricious fcntl()
X<getpriority> X<priority> X<nice>
Returns the current priority for a process, a process group, or a user.
-(See L<getpriority(2)>.) Will raise a fatal exception if used on a
+(See C<getpriority(2)>.) Will raise a fatal exception if used on a
machine that doesn't implement getpriority(2).
=item getpwnam NAME
EXPR is omitted, C<$_> is used. The C<< <*.c> >> operator is discussed in
more detail in L<perlop/"I/O Operators">.
+Note that C<glob> will split its arguments on whitespace, treating
+each segment as separate pattern. As such, C<glob('*.c *.h')> would
+match all files with a F<.c> or F<.h> extension. The expression
+C<glob('.* *')> would match all files in the current working directory.
+
Beginning with v5.6.0, this operator is implemented using the standard
-C<File::Glob> extension. See L<File::Glob> for details.
+C<File::Glob> extension. See L<File::Glob> for details, including
+C<bsd_glob> which does not treat whitespace as a pattern separator.
=item gmtime EXPR
X<gmtime> X<UTC> X<Greenwich>
alive (even if only as a zombie) and hasn't changed its UID. See
L<perlport> for notes on the portability of this construct.
-Unlike in the shell, if SIGNAL is negative, it kills
-process groups instead of processes. (On System V, a negative I<PROCESS>
-number will also kill process groups, but that's not portable.) That
-means you usually want to use positive not negative signals. You may also
-use a signal name in quotes.
+Unlike in the shell, if SIGNAL is negative, it kills process groups instead
+of processes. That means you usually want to use positive not negative signals.
+You may also use a signal name in quotes.
+
+The behavior of kill when a I<PROCESS> number is zero or negative depends on
+the operating system. For example, on POSIX-conforming systems, zero will
+signal the current process group and -1 will signal all processes.
See L<perlipc/"Signals"> for more details.
be placed in parentheses. See L<perlsub/"Temporary Values via local()">
for details, including issues with tied arrays and hashes.
+The C<delete local EXPR> construct can also be used to localize the deletion
+of array/hash elements to the current block.
+See L<perlsub/"Localized deletion of elements of composite types">.
+
=item localtime EXPR
X<localtime> X<ctime>
=item m//
-The match operator. See L<perlop>.
+The match operator. See L<perlop/"Regexp Quote-Like Operators">.
=item map BLOCK LIST
X<map>
You may also, in the Bourne shell tradition, specify an EXPR beginning
with C<< '>&' >>, in which case the rest of the string is interpreted
as the name of a filehandle (or file descriptor, if numeric) to be
-duped (as L<dup(2)>) and opened. You may use C<&> after C<< > >>,
+duped (as C<dup(2)>) and opened. You may use C<&> after C<< > >>,
C<<< >> >>>, C<< < >>, C<< +> >>, C<<< +>> >>>, and C<< +< >>.
The mode you specify should match the mode of the original filehandle.
(Duping a filehandle does not take into account any existing contents
If you specify C<< '<&=X' >>, where C<X> is a file descriptor number
or a filehandle, then Perl will do an equivalent of C's C<fdopen> of
-that file descriptor (and not call L<dup(2)>); this is more
+that file descriptor (and not call C<dup(2)>); this is more
parsimonious of file descriptors. For example:
# open for input, reusing the fileno of $fd
will have exactly the opposite restrictions.
-If you want a "real" C C<open> (see L<open(2)> on your system), then you
+If you want a "real" C C<open> (see C<open(2)> on your system), then you
should use the C<sysopen> function, which involves no such magic (but
may use subtly different filemodes than Perl open(), which is mapped
to C fopen()). This is
=item package NAMESPACE
X<package> X<module> X<namespace>
-=item package
-
Declares the compilation unit as being in the given namespace. The scope
of the package declaration is from the declaration itself through the end
of the enclosing block, file, or eval (the same as the C<my> operator).
=item qq/STRING/
-=item qr/STRING/
-
=item qx/STRING/
=item qw/STRING/
-Generalized quotes. See L<perlop/"Regexp Quote-Like Operators">.
+Generalized quotes. See L<perlop/"Quote-Like Operators">.
+
+=item qr/STRING/
+
+Regexp-like quote. See L<perlop/"Regexp Quote-Like Operators">.
=item quotemeta EXPR
X<quotemeta> X<metacharacter>
for (;;) {
undef $!;
unless (defined( $line = <> )) {
+ last if eof;
die $! if $!;
- last; # reached EOF
}
# ...
}
then this subroutine is expected to generate one line of source code per
call, writing the line into C<$_> and returning 1, then returning 0 at
"end of file". If there is a filehandle, then the subroutine will be
-called to act a simple source filter, with the line as read in C<$_>.
+called to act as a simple source filter, with the line as read in C<$_>.
Again, return 1 for each valid line, and 0 after all lines have been
returned.
}
# In the main program
- push @INC, new Foo(...);
+ push @INC, Foo->new(...);
Note that these hooks are also permitted to set the %INC entry
corresponding to the files they have loaded. See L<perlvar/%INC>.
elements of LIST and returns a string value with all characters
in the opposite order.
- print reverse <>; # line tac, last line first
+ print join(", ", reverse "world", "Hello"); # Hello, world
- undef $/; # for efficiency of <>
- print scalar reverse <>; # character tac, last line tsrif
+ print scalar reverse "dlrow ,", "olleH"; # Hello, world
Used without arguments in scalar context, reverse() reverses C<$_>.
+ $_ = "dlrow ,olleH";
+ print reverse; # No output, list context
+ print scalar reverse; # Hello, world
+
This operator is also handy for inverting a hash, although there are some
caveats. If a value is duplicated in the original hash, only one of those
can be represented as a key in the inverted hash. Also, this has to
=item s///
-The substitution operator. See L<perlop>.
+The substitution operator. See L<perlop/"Regexp Quote-Like Operators">.
=item say FILEHANDLE LIST
X<say>
disables the file descriptor in any forked copies in other
processes.
+Returns C<1> for success. In the case of error, returns C<undef> if
+the first argument is not a valid filehandle, or returns C<0> and sets
+C<$!> for any other failure.
+
=item sin EXPR
X<sin> X<sine> X<asin> X<arcsine>
=item sleep
Causes the script to sleep for EXPR seconds, or forever if no EXPR.
+Returns the number of seconds actually slept.
+
May be interrupted if the process receives a signal such as C<SIGALRM>.
-Returns the number of seconds actually slept. You probably cannot
-mix C<alarm> and C<sleep> calls, because C<sleep> is often implemented
-using C<alarm>.
+
+ eval {
+ local $SIG{ALARM} = sub { die "Alarm!\n" };
+ sleep;
+ };
+ die $@ unless $@ eq "Alarm!\n";
+
+You probably cannot mix C<alarm> and C<sleep> calls, because C<sleep>
+is often implemented using C<alarm>.
On some older systems, it may sleep up to a full second less than what
you requested, depending on how it counts seconds. Most modern systems
limited control of the sort. Its rather blunt control of the
underlying algorithm may not persist into future Perls, but the
ability to characterize the input or output in implementation
-independent ways quite probably will. See L<sort>.
+independent ways quite probably will. See L<the sort pragma|sort>.
Examples:
use sort '_mergesort'; # note discouraging _
@new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;
+Warning: syntactical care is required when sorting the list returned from
+a function. If you want to sort the list returned by the function call
+C<find_records(@key)>, you can use:
+
+ @contact = sort { $a cmp $b } find_records @key;
+ @contact = sort +find_records(@key);
+ @contact = sort &find_records(@key);
+ @contact = sort(find_records(@key));
+
+If instead you want to sort the array @key with the comparison routine
+C<find_records()> then you can use:
+
+ @contact = sort { find_records() } @key;
+ @contact = sort find_records(@key);
+ @contact = sort(find_records @key);
+ @contact = sort(find_records (@key));
+
If you're using strict, you I<must not> declare $a
and $b as lexicals. They are package globals. That means
-if you're in the C<main> package and type
+that if you're in the C<main> package and type
@articles = sort {$b <=> $a} @files;
default, empty leading fields are preserved, and empty trailing ones are
deleted. (If all fields are empty, they are considered to be trailing.)
-In scalar context, returns the number of fields found and splits into
-the C<@_> array. Use of split in scalar context is deprecated, however,
-because it clobbers your subroutine arguments.
+In scalar context, returns the number of fields found.
If EXPR is omitted, splits the C<$_> string. If PATTERN is also omitted,
splits on whitespace (after skipping any leading whitespace). Anything
matching a null string) will split the value of EXPR into separate
characters at each point it matches that way. For example:
- print join(':', split(/ */, 'hi there'));
+ print join(':', split(/ */, 'hi there')), "\n";
produces the output 'h:i:t:h:e:r:e'.
of C<//> to mean "the last successful pattern match". So, for C<split>,
the following:
- print join(':', split(//, 'hi there'));
+ print join(':', split(//, 'hi there')), "\n";
produces the output 'h:i: :t:h:e:r:e'.
when LIMIT is given and is not 0), regardless of the length of the match.
For example:
- print join(':', split(//, 'hi there!', -1));
- print join(':', split(/\W/, 'hi there!', -1));
+ print join(':', split(//, 'hi there!', -1)), "\n";
+ print join(':', split(/\W/, 'hi there!', -1)), "\n";
produce the output 'h:i: :t:h:e:r:e:!:' and 'hi:there:', respectively,
both with an empty trailing field.
If you had the entire header of a normal Unix email message in $header,
you could split it up into fields and their values this way:
- $header =~ s/\n\s+/ /g; # fix continuation lines
+ $header =~ s/\n(?=\s)//g; # fix continuation lines
%hdrs = (UNIX_FROM => split /^(\S*?):\s*/m, $header);
The pattern C</PATTERN/> may be replaced with an expression to specify
Returns a string formatted by the usual C<printf> conventions of the C
library function C<sprintf>. See below for more details
-and see
L<sprintf(3)> or L<printf(3)> on your system for an explanation of
+and see
C<sprintf(3)> or C<printf(3)> on your system for an explanation of
the general principles.
For example:
indicates a failure to start the program or an error of the wait(2) system
call (inspect $! for the reason).
+If you'd like to make C<system> (and many other bits of Perl) die on error,
+have a look at the L<autodie> pragma.
+
Like C<exec>, C<system> allows you to lie to a program about its name if
you use the C<system PROGRAM LIST> syntax. Again, see L</exec>.
system(@args) == 0
or die "system @args failed: $?"
-You can check all the failure possibilities by inspecting
-C<$?> like this:
+If you'd like to manually inspect C<system>'s failure, you can check all
+possible failure modes by inspecting C<$?> like this:
if ($? == -1) {
print "failed to execute: $!\n";
=item tr///
-The transliteration operator. Same as C<y///>. See L<perlop>.
+The transliteration operator. Same as C<y///>. See
+L<perlop/"Quote and Quote-like Operators">.
=item truncate FILEHANDLE,LENGTH
X<truncate>
Also, if the specified perl version is greater than or equal to 5.9.5,
C<use VERSION> will also load the C<feature> pragma and enable all
features available in the requested version. See L<feature>.
+Similarly, if the specified perl version is greater than or equal to
+5.11.0, strictures are enabled lexically as with C<use strict> (except
+that the F<strict.pm> file is not actually loaded).
The C<BEGIN> forces the C<require> and C<import> to happen at compile time. The
C<require> makes sure the module is loaded into memory if it hasn't been
Behaves like the wait(2) system call on your system: it waits for a child
process to terminate and returns the pid of the deceased process, or
C<-1> if there are no child processes. The status is returned in C<$?>
-and C<{^CHILD_ERROR_NATIVE}>.
+and C<${^CHILD_ERROR_NATIVE}>.
Note that a return value of C<-1> could mean that child processes are
being automatically reaped, as described in L<perlipc>.
Waits for a particular child process to terminate and returns the pid of
the deceased process, or C<-1> if there is no such child process. On some
systems, a value of 0 indicates that there are processes still running.
-The status is returned in C<$?> and C<{^CHILD_ERROR_NATIVE}>. If you say
+The status is returned in C<$?> and C<${^CHILD_ERROR_NATIVE}>. If you say
use POSIX ":sys_wait_h";
#...
=item y///
-The transliteration operator. Same as C<tr///>. See L<perlop>.
+The transliteration operator. Same as C<tr///>. See
+L<perlop/"Quote and Quote-like Operators">.
=back
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