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<gethostent>,
-C<getlogin>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>,
+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<getprgp>, C<getpriority>, C<getprotobynumber>,
C<getprotoent>, C<getpwent>, C<getpwnam>, C<getpwuid>,
C<getservbyport>, C<getservent>, C<getsockopt>, C<glob>, C<ioctl>,
=over 8
-=item I<-X> FILEHANDLE
+=item -X FILEHANDLE
-=item I<-X> EXPR
+=item -X EXPR
-=item I<-X>
+=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
# didn't
}
+For more information see L<perlipc>.
+
=item atan2 Y,X
Returns the arctangent of Y/X in the range -PI to PI.
Closes a directory opened by C<opendir> and returns the success of that
system call.
-DIRHANDLE may be an expression whose value can be used as an indirect
-dirhandle, usually the real dirhandle name.
-
=item connect SOCKET,NAME
Attempts to connect to a remote socket, just as the connect system call
When verifying an existing encrypted string you should use the
encrypted text as the salt (like C<crypt($plain, $crypted) eq
-$crypted>). This allows your code to work with the standard L<crypt|\crypt>
+$crypted>). This allows your code to work with the standard L<crypt|/crypt>
and with more exotic implementations. In other words, do not assume
anything about the returned string itself, or how many bytes in
the encrypted string matter.
Of course, typing in your own password to whoever asks you
for it is unwise.
-The L<crypt|\crypt> function is unsuitable for encrypting large quantities
+The L<crypt|/crypt> function is unsuitable for encrypting large quantities
of data, not least of all because you can't get the information
back. Look at the F<by-module/Crypt> and F<by-module/PGP> directories
on your favorite CPAN mirror for a slew of potentially useful
(The following is a comprehensive reference to open(): for a gentler
introduction you may consider L<perlopentut>.)
-If FILEHANDLE is an undefined lexical (C<my>) variable the variable is
-assigned a reference to a new anonymous filehandle, otherwise if
-FILEHANDLE is an expression, its value is used as the name of the real
-filehandle wanted. (This is considered a symbolic reference, so C<use
-strict 'refs'> should I<not> be in effect.)
+If FILEHANDLE is an undefined scalar variable (or array or hash element)
+the variable is assigned a reference to a new anonymous filehandle,
+otherwise if FILEHANDLE is an expression, its value is used as the name of
+the real filehandle wanted. (This is considered a symbolic reference, so
+C<use strict 'refs'> should I<not> be in effect.)
If EXPR is omitted, the scalar variable of the same name as the
FILEHANDLE contains the filename. (Note that lexical variables--those
Opens a directory named EXPR for processing by C<readdir>, C<telldir>,
C<seekdir>, C<rewinddir>, and C<closedir>. Returns true if successful.
+DIRHANDLE may be an expression whose value can be used as an indirect
+dirhandle, usually the real dirhandle name. If DIRHANDLE is an undefined
+scalar variable (or array or hash element), the variable is assigned a
+reference to a new anonymous dirhandle.
DIRHANDLEs have their own namespace separate from FILEHANDLEs.
=item ord EXPR
x A null byte.
X Back up a byte.
- @ Null fill to absolute position.
+ @ Null fill to absolute position, counted from the start of
+ the innermost ()-group.
( Start of a ()-group.
The following rules apply:
integer-packing ones like C<n> (for Java strings), C<w> (for ASN.1 or
SNMP) and C<N> (for Sun XDR).
-The I<string-item> must, at present, be C<"A*">, C<"a*"> or C<"Z*">.
-For C<unpack> the length of the string is obtained from the I<length-item>,
-but if you put in the '*' it will be ignored.
+For C<pack>, the I<string-item> must, at present, be C<"A*">, C<"a*"> or
+C<"Z*">. For C<unpack> the length of the string is obtained from the
+I<length-item>, but if you put in the '*' it will be ignored. For all other
+codes, C<unpack> applies the length value to the next item, which must not
+have a repeat count.
unpack 'C/a', "\04Gurusamy"; gives 'Guru'
unpack 'a3/A* A*', '007 Bond J '; gives (' Bond','J')
print $Config{longsize}, "\n";
print $Config{longlongsize}, "\n";
-(The C<$Config{longlongsize}> will be undefine if your system does
+(The C<$Config{longlongsize}> will be undefined if your system does
not support long longs.)
=item *
=item *
A ()-group is a sub-TEMPLATE enclosed in parentheses. A group may
-take a repeat count, both as postfix, and via the C</> template
-character.
+take a repeat count, both as postfix, and for unpack() also via the C</>
+template character. Within each repetition of a group, positioning with
+C<@> starts again at 0. Therefore, the result of
+
+ pack( '@1A((@2A)@3A)', 'a', 'b', 'c' )
+
+is the string "\0a\0\0bc".
+
=item *
=item *
A comment in a TEMPLATE starts with C<#> and goes to the end of line.
+White space may be used to separate pack codes from each other, but
+a C<!> modifier and a repeat count must follow immediately.
=item *
$line = <STDIN>;
$line = readline(*STDIN); # same thing
+If readline encounters an operating system error, C<$!> will be set with the
+corresponding error message. It can be helpful to check C<$!> when you are
+reading from filehandles you don't trust, such as a tty or a socket. The
+following example uses the operator form of C<readline>, and takes the necessary
+steps to ensure that C<readline> was successful.
+
+ for (;;) {
+ undef $!;
+ unless (defined( $line = <> )) {
+ die $! if $!;
+ last; # reached EOF
+ }
+ # ...
+ }
+
=item readlink EXPR
=item readlink
past the end of the array, perl issues a warning, and splices at the
end of the array.
-The following equivalences hold (assuming C<$[ == 0>):
+The following equivalences hold (assuming C<< $[ == 0 and $#a >= $i >> )
push(@a,$x,$y) splice(@a,@a,0,$x,$y)
pop(@a) splice(@a,-1)
shift(@a) splice(@a,0,1)
unshift(@a,$x,$y) splice(@a,0,0,$x,$y)
- $a[$x] = $y splice(@a,$x,1,$y)
+ $a[$i] = $y splice(@a,$i,1,$y)
Example, assuming array lengths are passed before arrays:
Suitable for feeding to C<gmtime> and C<localtime>.
For measuring time in better granularity than one second,
-you may use either the Time::HiRes module from CPAN, or
-if you have gettimeofday(2), you may be able to use the
-C<syscall> interface of Perl, see L<perlfaq8> for details.
+you may use either the Time::HiRes module (from CPAN, and starting from
+Perl 5.8 part of the standard distribution), or if you have
+gettimeofday(2), you may be able to use the C<syscall> interface of Perl.
+See L<perlfaq8> for details.
=item times
corresponds to a valid memory location, passing a pointer value that's
not known to be valid is likely to have disastrous consequences.
-If the repeat count of a field is larger than what the remainder of
-the input string allows, repeat count is decreased. If the input string
-is longer than one described by the TEMPLATE, the rest is ignored.
+If there are more pack codes or if the repeat count of a field or a group
+is larger than what the remainder of the input string allows, the result
+is not well defined: in some cases, the repeat count is decreased, or
+C<unpack()> will produce null strings or zeroes, or terminate with an
+error. If the input string is longer than one described by the TEMPLATE,
+the rest is ignored.
See L</pack> for more examples and notes.
files. The first two elements of the list must be the NUMERICAL access
and modification times, in that order. Returns the number of files
successfully changed. The inode change time of each file is set
-to the current time. This code has the same effect as the C<touch>
-command if the files already exist:
+to the current time. For example, this code has the same effect as the
+Unix touch(1) command when the files I<already exist>.
#!/usr/bin/perl
$now = time;
utime $now, $now, @ARGV;
-If the first two elements of the list are C<undef>, then the utime(2)
-function in the C library will be called with a null second argument.
-On most systems, this will set the file's access and modification
-times to the current time. (i.e. equivalent to the example above.)
+B<Note:> Under NFS, touch(1) uses the time of the NFS server, not
+the time of the local machine. If there is a time synchronization
+problem, the NFS server and local machine will have different times.
+
+Since perl 5.7.2, if the first two elements of the list are C<undef>, then
+the utime(2) function in the C library will be called with a null second
+argument. On most systems, this will set the file's access and
+modification times to the current time (i.e. equivalent to the example
+above.)
utime undef, undef, @ARGV;
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