operator. A unary operator generally provides a scalar context to its
argument, while a list operator may provide either scalar and 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 only
-ever be one list argument.) For instance, splice() has three scalar
+be first, and the list argument will follow. (Note that there can ever
+be only one list argument.) For instance, splice() has three scalar
arguments followed by a list.
In the syntax descriptions that follow, list operators that expect a
Any function in the list below may be used either with or without
parentheses around its arguments. (The syntax descriptions omit the
-parens.) If you use the parens, the simple (but occasionally
+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
read, write or execute the file. Also note that, for the superuser,
C<-r>, C<-R>, C<-w> and C<-W> always return 1, and C<-x> and C<-X> return
1 if any execute bit is set in the mode. Scripts run by the superuser may
-thus need to do a stat() in order to determine the actual mode of the
+thus need to do a stat() to determine the actual mode of the
file, or temporarily set the uid to something else.
Example:
The C<-T> and C<-B> switches work as follows. The first block or so of the
file is examined for odd characters such as strange control codes or
-characters with the high bit set. If too many odd characters (>30%)
+characters with the high bit set. If too many odd characters (E<gt>30%)
are found, it's a C<-B> file, otherwise it's a C<-T> file. Also, any file
containing null in the first block is considered a binary file. If C<-T>
or C<-B> is used on a filehandle, the current stdio buffer is examined
=item abs VALUE
+=item abs
+
Returns the absolute value of its argument.
+If VALUE is omitted, uses $_.
=item accept NEWSOCKET,GENERICSOCKET
=item alarm SECONDS
+=item alarm
+
Arranges to have a SIGALRM delivered to this process after the
-specified number of seconds have elapsed. (On some machines,
+specified number of seconds have elapsed. If SECONDS is not specified,
+the value stored in $_ is used. (On some machines,
unfortunately, the elapsed time may be up to one second less than you
specified because of how seconds are counted.) Only one timer may be
counting at once. Each call disables the previous timer, and an
or else see L</select()> below. It is not advised to intermix alarm()
and sleep() calls.
+If you want to use alarm() to time out a system call you need to use an
+eval/die pair. You can't rely on the alarm causing the system call to
+fail with $! set to EINTR because Perl sets up signal handlers to
+restart system calls on some systems. Using eval/die always works.
+
+ eval {
+ local $SIG{ALRM} = sub { die "alarm\n" }; # NB \n required
+ alarm $timeout;
+ $nread = sysread SOCKET, $buffer, $size;
+ alarm 0;
+ };
+ die if $@ && $@ ne "alarm\n"; # propagate errors
+ if ($@) {
+ # timed out
+ }
+ else {
+ # didn't
+ }
+
=item atan2 Y,X
Returns the arctangent of Y/X in the range -PI to PI.
This function tells the referenced object (passed as REF) that it is now
an object in the CLASSNAME package--or the current package if no CLASSNAME
is specified, which is often the case. It returns the reference for
-convenience, since a bless() is often the last thing in a constructor.
+convenience, because a bless() is often the last thing in a constructor.
Always use the two-argument version if the function doing the blessing
might be inherited by a derived class. See L<perlobj> for more about the
blessing (and blessings) of objects.
=item chr NUMBER
+=item chr
+
Returns the character represented by that NUMBER in the character set.
For example, C<chr(65)> is "A" in ASCII.
+If NUMBER is omitted, uses $_.
+
=item chroot FILENAME
+=item chroot
+
This function works as the system call by the same name: it makes the
named directory the new root directory for all further pathnames that
begin with a "/" by your process and all of its children. (It doesn't
Closes the file or pipe associated with the file handle, returning TRUE
only if stdio successfully flushes buffers and closes the system file
descriptor. You don't have to close FILEHANDLE if you are immediately
-going to do another open() on it, since open() will close it for you. (See
+going to do another open() on it, because open() will close it for you. (See
open().) However, an explicit close on an input file resets the line
counter ($.), while the implicit close done by open() does not. Also,
closing a pipe will wait for the process executing on the pipe to
print "ok\n";
}
-Of course, typing in your own password to whoever asks you
+Of course, typing in your own password to whomever asks you
for it is unwise.
=item dbmclose ASSOC_ARRAY
looks like one). DBNAME is the name of the database (without the F<.dir>
or F<.pag> extension if any). If the database does not exist, it is
created with protection specified by MODE (as modified by the umask()).
-If your system only supports the older DBM functions, you may perform only
+If your system supports only the older DBM functions, you may perform only
one dbmopen() in your program. In older versions of Perl, if your system
had neither DBM nor ndbm, calling dbmopen() produced a fatal error; it now
falls back to sdbm(3).
dbmclose(%HIST);
See also L<AnyDBM_File> for a more general description of the pros and
-cons of the various dbm apparoches, as well as L<DB_File> for a particularly
+cons of the various dbm approaches, as well as L<DB_File> for a particularly
rich implementation.
=item defined EXPR
+=item defined
+
Returns a boolean value saying whether EXPR has a real value
-or not. Many operations return the undefined value under exceptional
-conditions, such as end of file, uninitialized variable, system error
-and such. This function allows you to distinguish between an undefined
+or not. If EXPR is not present, $_ will be checked. Many operations
+return the undefined value under exceptional conditions, such as end of
+file, uninitialized variable, system error and such. This function
+allows you to distinguish between an undefined
null scalar and a defined null scalar with operations that might return
a real null string, such as referencing elements of an array. You may
also check to see if arrays or subroutines exist. Use of defined on
matched something that happened to be 0 characters long. This is all
very above-board and honest. When a function returns an undefined value,
it's an admission that it couldn't give you an honest answer. So
-you should only use defined() when you're questioning the integrity
+you should use defined() only when you're questioning the integrity
of what you're trying to do. At other times, a simple comparison to
0 or "" is what you want.
=item die LIST
Outside of an eval(), prints the value of LIST to C<STDERR> and exits with
-the current value of $! (errno). If $! is 0, exits with the value of
-C<($? E<gt>E<gt> 8)> (backtick `command` status). If C<($? E<gt>E<gt> 8)> is 0,
+the current value of C<$!> (errno). If C<$!> is 0, exits with the value of
+C<($? E<gt>E<gt> 8)> (back-tick `command` status). If C<($? E<gt>E<gt> 8)> is 0,
exits with 255. Inside an eval(), the error message is stuffed into C<$@>,
and the eval() is terminated with the undefined value; this makes die()
the way to raise an exception.
current filename for error messages, and searches all the B<-I>
libraries if the file isn't in the current directory (see also the @INC
array in L<perlvar/Predefined Names>). It's the same, however, in that it does
-reparse the file every time you call it, so you probably don't want to
+re-parse the file every time you call it, so you probably don't want to
do this inside a loop.
Note that inclusion of library modules is better done with the
When called in a list context, returns a 2-element array consisting
of the key and value for the next element of an associative array,
so that you can iterate over it. When called in a scalar context,
-returns the key only for the next element in the associative array.
+returns the key for only the next element in the associative array.
Entries are returned in an apparently random order. When the array is
entirely read, a null array is returned in list context (which when
assigned produces a FALSE (0) value), and C<undef> is returned in a
An C<eof> without an argument uses the last file read as argument.
Empty parentheses () may be used to indicate
-the pseudofile formed of the files listed on the command line, i.e.
+the pseudo file formed of the files listed on the command line, i.e.,
C<eof()> is reasonable to use inside a while (E<lt>E<gt>) loop to detect the end
of only the last file. Use C<eof(ARGV)> or eof without the parentheses to
test I<EACH> file in a while (E<lt>E<gt>) loop. Examples:
is executed in the context of the current Perl program, so that any
variable settings, subroutine or format definitions remain afterwards.
The value returned is the value of the last expression evaluated, or a
-return statement may be used, just as with subroutines.
+return statement may be used, just as with subroutines. The last
+expression is evaluated in scalar or array context, depending on the
+context of the eval.
If there is a syntax error or runtime error, or a die() statement is
executed, an undefined value is returned by eval(), and C<$@> is set to the
string. If EXPR is omitted, evaluates $_. The final semicolon, if
any, may be omitted from the expression.
-Note that, since eval() traps otherwise-fatal errors, it is useful for
+Note that, because eval() traps otherwise-fatal errors, it is useful for
determining whether a particular feature (such as socket() or symlink())
is implemented. It is also Perl's exception trapping mechanism, where
the die operator is used to raise exceptions.
Cases 1 and 2 above behave identically: they run the code contained in the
variable $x. (Although case 2 has misleading double quotes making the
reader wonder what else might be happening (nothing is).) Cases 3 and 4
-likewise behave in the same way: they run the code <$x>, which does
+likewise behave in the same way: they run the code E<lt>$xE<gt>, which does
nothing at all. (Case 4 is preferred for purely visual reasons.) Case 5
is a place where normally you I<WOULD> like to use double quotes, except
that in that particular situation, you can just use symbolic references
=item exec LIST
-The exec() function executes a system command I<AND NEVER RETURNS>. Use
-the system() function if you want it to return.
+The exec() function executes a system command I<AND NEVER RETURNS>,
+unless the command does not exist and is executed directly instead of
+via C</bin/sh -c> (see below). Use system() instead of exec() if you
+want it to return.
If there is more than one argument in LIST, or if LIST is an array with
more than one value, calls execvp(3) with the arguments in LIST. If
print "Defined\n" if defined $array{$key};
print "True\n" if $array{$key};
-A hash element can only be TRUE if it's defined, and defined if
+A hash element can be TRUE only if it's defined, and defined if
it exists, but the reverse doesn't necessarily hold true.
Note that the EXPR can be arbitrarily complicated as long as the final
=item exp EXPR
+=item exp
+
Returns I<e> (the natural logarithm base) to the power of EXPR.
If EXPR is omitted, gives C<exp($_)>.
fatal error if used on a machine that doesn't implement either flock(2) or
fcntl(2). The fcntl(2) system call will be automatically used if flock(2)
is missing from your system. This makes flock() the portable file locking
-strategy, although it will only lock entire files, not records. Note also
+strategy, although it will lock only entire files, not records. Note also
that some versions of flock() cannot lock things over the network; you
would need to use the more system-specific fcntl() for that.
.
$str = "widget";
- $num = $cost/$quantiy;
+ $num = $cost/$quantity;
$~ = 'Something';
write;
You may therefore need to use multiple formlines to implement a single
record format, just like the format compiler.
-Be careful if you put double quotes around the picture, since an "C<@>"
+Be careful if you put double quotes around the picture, because an "C<@>"
character may be taken to mean the beginning of an array name.
formline() always returns TRUE. See L<perlform> for other examples.
system "stty -cbreak </dev/tty >/dev/tty 2>&1";
}
else {
- system "stty", 'icanon', 'eol', '^@'; # ascii null
+ system "stty", 'icanon', 'eol', '^@'; # ASCII null
}
print "\n";
=item glob EXPR
Returns the value of EXPR with filename expansions such as a shell
-would do. This is the internal function implementing the <*.*>
+would do. This is the internal function implementing the E<lt>*.*E<gt>
operator, except it's easier to use.
=item gmtime EXPR
Converts a time as returned by the time function to a 9-element array
-with the time localized for the standard Greenwich timezone.
+with the time localized for the standard Greenwich time zone.
Typically used as follows:
@foo = grep {!/^#/} @bar; # weed out comments
-Note that, since $_ is a reference into the list value, it can be used
+Note that, because $_ is a reference into the list value, it can be used
to modify the elements of the array. While this is useful and
supported, it can cause bizarre results if the LIST is not a named
array.
=item hex EXPR
+=item hex
+
Interprets EXPR as a hex string and returns the corresponding decimal
value. (To convert strings that might start with 0 or 0x see
oct().) If EXPR is omitted, uses $_.
Returns the position of the first occurrence of SUBSTR in STR at or after
POSITION. If POSITION is omitted, starts searching from the beginning of
-the string. The return value is based at 0 (or whatever you've set the $[
+the string. The return value is based at 0 (or whatever you've set the C<$[>
variable to--but don't do that). If the substring is not found, returns
one less than the base, ordinarily -1.
=item int EXPR
+=item int
+
Returns the integer portion of EXPR. If EXPR is omitted, uses $_.
=item ioctl FILEHANDLE,FUNCTION,SCALAR
printf "%4d %s\n", $hash{$key}, $key;
}
+As an lvalue C<keys> allows you to increase the number of hash buckets
+allocated for the given associative array. This can gain you a measure
+of efficiency if you know the hash is going to get big. (This is
+similar to pre-extending an array by assigning a larger number to
+$#array.) If you say
+
+ keys %hash = 200;
+
+then C<%hash> will have at least 200 buckets allocated for it. These
+buckets will be retained even if you do C<%hash = ()>, use C<undef
+%hash> if you want to free the storage while C<%hash> is still in scope.
+You can't shrink the number of buckets allocated for the hash using
+C<keys> in this way (but you needn't worry about doing this by accident,
+as trying has no effect).
+
=item kill LIST
Sends a signal to a list of processes. The first element of
=item lc EXPR
+=item lc
+
Returns an lowercased version of EXPR. This is the internal function
implementing the \L escape in double-quoted strings.
Should respect any POSIX setlocale() settings.
+If EXPR is omitted, uses $_.
+
=item lcfirst EXPR
+=item lcfirst
+
Returns the value of EXPR with the first character lowercased. This is
the internal function implementing the \l escape in double-quoted strings.
Should respect any POSIX setlocale() settings.
+If EXPR is omitted, uses $_.
+
=item length EXPR
+=item length
+
Returns the length in characters of the value of EXPR. If EXPR is
omitted, returns length of $_.
A local modifies the listed variables to be local to the enclosing block,
subroutine, C<eval{}> or C<do>. If more than one value is listed, the
-list must be placed in parens. See L<perlsub/"Temporary Values via
+list must be placed in parentheses. See L<perlsub/"Temporary Values via
local()"> for details.
But you really probably want to be using my() instead, because local() isn't
=item localtime EXPR
Converts a time as returned by the time function to a 9-element array
-with the time analyzed for the local timezone. Typically used as
+with the time analyzed for the local time zone. Typically used as
follows:
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
In a scalar context, prints out the ctime(3) value:
- $now_string = localtime; # e.g. "Thu Oct 13 04:54:34 1994"
+ $now_string = localtime; # e.g., "Thu Oct 13 04:54:34 1994"
Also see the F<timelocal.pl> library, and the strftime(3) function available
via the POSIX module.
=item log EXPR
+=item log
+
Returns logarithm (base I<e>) of EXPR. If EXPR is omitted, returns log
of $_.
=item lstat EXPR
+=item lstat
+
Does the same thing as the stat() function, but stats a symbolic link
instead of the file the symbolic link points to. If symbolic links are
unimplemented on your system, a normal stat() is done.
+If EXPR is omitted, stats $_.
+
=item m//
The match operator. See L<perlop>.
Creates the directory specified by FILENAME, with permissions specified
by MODE (as modified by umask). If it succeeds it returns 1, otherwise
-it returns 0 and sets $! (errno).
+it returns 0 and sets C<$!> (errno).
=item msgctl ID,CMD,ARG
A "my" declares the listed variables to be local (lexically) to the
enclosing block, subroutine, C<eval>, or C<do/require/use>'d file. If
-more than one value is listed, the list must be placed in parens. See
+more than one value is listed, the list must be placed in parentheses. See
L<perlsub/"Private Variables via my()"> for details.
=item next LABEL
=item oct EXPR
+=item oct
+
Interprets EXPR as an octal string and returns the corresponding
decimal value. (If EXPR happens to start off with 0x, interprets it as
a hex string instead.) The following will handle decimal, octal, and
FILEHANDLE. If FILEHANDLE is an expression, its value is used as the name
of the real filehandle wanted. If EXPR is omitted, the scalar variable of
the same name as the FILEHANDLE contains the filename. If the filename
-begins with "<" or nothing, the file is opened for input. If the filename
-begins with ">", the file is opened for output. If the filename begins
-with ">>", the file is opened for appending. You can put a '+' in front
-of the '>' or '<' to indicate that you want both read and write access to
-the file; thus '+<' is usually preferred for read/write updates--the '+>'
-mode would clobber the file first. These correspond to the fopen(3) modes
-of 'r', 'r+', 'w', 'w+', 'a', and 'a+'.
+begins with "E<lt>" or nothing, the file is opened for input. If the filename
+begins with "E<gt>", the file is opened for output. If the filename begins
+with "E<gt>E<gt>", the file is opened for appending. You can put a '+' in
+front of the 'E<gt>' or 'E<lt>' to indicate that you want both read and write
+access to the file; thus '+E<lt>' is usually preferred for read/write
+updates--the '+E<gt>' mode would clobber the file first. These correspond to
+the fopen(3) modes of 'r', 'r+', 'w', 'w+', 'a', and 'a+'.
If the filename begins with "|", the filename is interpreted
as a command to which output is to be piped, and if the filename ends with
not have a raw open() to a command that pipes both in I<and> out, but see L<open2>,
L<open3>, and L<perlipc/"Bidirectional Communication"> for alternatives.)
-Opening '-' opens STDIN and opening '>-' opens STDOUT. Open returns
+Opening '-' opens STDIN and opening 'E<gt>-' opens STDOUT. Open returns
non-zero upon success, the undefined value otherwise. If the open
involved a pipe, the return value happens to be the pid of the
subprocess.
}
You may also, in the Bourne shell tradition, specify an EXPR beginning
-with ">&", in which case the rest of the string is interpreted as the
+with "E<gt>&", in which case the rest of the string is interpreted as the
name of a filehandle (or file descriptor, if numeric) which is to be
-duped and opened. You may use & after >, >>, <, +>, +>> and +<. The
+duped and opened. You may use & after E<gt>, E<gt>E<gt>, E<lt>, +E<gt>,
++E<gt>E<gt> and +E<lt>. The
mode you specify should match the mode of the original filehandle.
-(Duping a filehandle does not take into acount any existing contents of
+(Duping a filehandle does not take into account any existing contents of
stdio buffers.)
Here is a script that saves, redirects, and restores STDOUT and
STDERR:
print STDERR "stderr 2\n";
-If you specify "<&=N", where N is a number, then Perl will do an
+If you specify "E<lt>&=N", where N is a number, then Perl will do an
equivalent of C's fdopen() of that file descriptor; this is more
parsimonious of file descriptors. For example:
open(FILEHANDLE, "<&=$fd")
-If you open a pipe on the command "-", i.e. either "|-" or "-|", then
+If you open a pipe on the command "-", i.e., either "|-" or "-|", then
there is an implicit fork done, and the return value of open is the pid
of the child within the parent process, and 0 within the child
-process. (Use defined($pid) to determine whether the open was successful.)
+process. (Use C<defined($pid)> to determine whether the open was successful.)
The filehandle behaves normally for the parent, but i/o to that
filehandle is piped from/to the STDOUT/STDIN of the child process.
In the child process the filehandle isn't opened--i/o happens from/to
See L<perlipc/"Safe Pipe Opens"> for more examples of this.
Explicitly closing any piped filehandle causes the parent process to
-wait for the child to finish, and returns the status value in $?.
+wait for the child to finish, and returns the status value in C<$?>.
Note: on any operation which may do a fork, unflushed buffers remain
-unflushed in both processes, which means you may need to set $| to
+unflushed in both processes, which means you may need to set C<$|> to
avoid duplicate output.
Using the FileHandle constructor from the FileHandle package,
}
The filename that is passed to open will have leading and trailing
-whitespace deleted. In order to open a file with arbitrary weird
+whitespace deleted. To open a file with arbitrary weird
characters in it, it's necessary to protect any leading and trailing
whitespace thusly:
=item ord EXPR
+=item ord
+
Returns the numeric ascii value of the first character of EXPR. If
EXPR is omitted, uses $_.
u A uuencoded string.
+ w A BER compressed integer. Bytes give an unsigned integer base
+ 128, most significant digit first, with as few digits as
+ possible, and with the bit 8 of each byte except the last set
+ to "1."
+
x A null byte.
X Back up a byte.
@ Null fill to absolute position.
both use IEEE floating point arithmetic (as the endian-ness of the memory
representation is not part of the IEEE spec). Note that Perl uses doubles
internally for all numeric calculation, and converting from double into
-float and thence back to double again will lose precision (i.e.
+float and thence back to double again will lose precision (i.e.,
C<unpack("f", pack("f", $foo)>) will not in general equal $foo).
Examples:
of the package declaration is from the declaration itself through the end of
the enclosing block (the same scope as the local() operator). All further
unqualified dynamic identifiers will be in this namespace. A package
-statement only affects dynamic variables--including those you've used
+statement affects only dynamic variables--including those you've used
local() on--but I<not> lexical variables created with my(). Typically it
would be the first declaration in a file to be included by the C<require>
or C<use> operator. You can switch into a package in more than one place;
-it merely influences which symbol table is used by the compiler for the
+it influences merely which symbol table is used by the compiler for the
rest of that block. You can refer to variables and filehandles in other
packages by prefixing the identifier with the package name and a double
colon: C<$Package::Variable>. If the package name is null, the C<main>
Opens a pair of connected pipes like the corresponding system call.
Note that if you set up a loop of piped processes, deadlock can occur
unless you are very careful. In addition, note that Perl's pipes use
-stdio buffering, so you may need to set $| to flush your WRITEHANDLE
+stdio buffering, so you may need to set C<$|> to flush your WRITEHANDLE
after each command, depending on the application.
See L<open2>, L<open3>, and L<perlipc/"Bidirectional Communication">
=item pos SCALAR
+=item pos
+
Returns the offset of where the last C<m//g> search left off for the variable
-in question. May be modified to change that offset.
+is in question ($_ is used when the variable is not specified). May be
+modified to change that offset.
=item print FILEHANDLE LIST
the variable contains the name of or a reference to the filehandle, thus introducing one
level of indirection. (NOTE: If FILEHANDLE is a variable and the next
token is a term, it may be misinterpreted as an operator unless you
-interpose a + or put parens around the arguments.) If FILEHANDLE is
+interpose a + or put parentheses around the arguments.) If FILEHANDLE is
omitted, prints by default to standard output (or to the last selected
output channel--see L</select>). If LIST is also omitted, prints $_ to
STDOUT. To set the default output channel to something other than
evaluated in a list context. Also be careful not to follow the print
keyword with a left parenthesis unless you want the corresponding right
parenthesis to terminate the arguments to the print--interpose a + or
-put parens around all the arguments.
+put parentheses around all the arguments.
Note that if you're storing FILEHANDLES in an array or other expression,
you will have to use a block returning its value instead:
=item prototype FUNCTION
Returns the prototype of a function as a string (or C<undef> if the
-function has no prototype). FUNCTION is a reference to the the
+function has no prototype). FUNCTION is a reference to the
function whose prototype you want to retrieve.
=item push ARRAY,LIST
=item quotemeta EXPR
+=item quotemeta
+
Returns the value of EXPR with with all regular expression
metacharacters backslashed. This is the internal function implementing
the \Q escape in double-quoted strings.
+If EXPR is omitted, uses $_.
+
=item rand EXPR
=item rand
a scalar context or a null list in a list context.
If you're planning to filetest the return values out of a readdir(), you'd
-better prepend the directory in question. Otherwise, since we didn't
+better prepend the directory in question. Otherwise, because we didn't
chdir() there, it would have been testing the wrong file.
opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!";
=item readlink EXPR
+=item readlink
+
Returns the value of a symbolic link, if symbolic links are
implemented. If not, gives a fatal error. If there is some system
-error, returns the undefined value and sets $! (errno). If EXPR is
+error, returns the undefined value and sets C<$!> (errno). If EXPR is
omitted, uses $_.
=item recv SOCKET,SCALAR,LEN,FLAGS
=item ref EXPR
-Returns a TRUE value if EXPR is a reference, FALSE otherwise. The value
-returned depends on the type of thing the reference is a reference to.
+=item ref
+
+Returns a TRUE value if EXPR is a reference, FALSE otherwise. If EXPR
+is not specified, $_ will be used. The value returned depends on the
+type of thing the reference is a reference to.
Builtin types include:
REF
=item rename OLDNAME,NEWNAME
Changes the name of a file. Returns 1 for success, 0 otherwise. Will
-not work across filesystem boundaries.
+not work across file system boundaries.
=item require EXPR
Demands some semantics specified by EXPR, or by $_ if EXPR is not
supplied. If EXPR is numeric, demands that the current version of Perl
-($] or $PERL_VERSION) be equal or greater than EXPR.
+(C<$]> or $PERL_VERSION) be equal or greater than EXPR.
Otherwise, demands that a library file be included if it hasn't already
been included. The file is included via the do-FILE mechanism, which is
expression is interpreted as a list of single characters (hyphens
allowed for ranges). All variables and arrays beginning with one of
those letters are reset to their pristine state. If the expression is
-omitted, one-match searches (?pattern?) are reset to match again. Only
-resets variables or searches in the current package. Always returns
+omitted, one-match searches (?pattern?) are reset to match again. Resets
+only variables or searches in the current package. Always returns
1. Examples:
reset 'X'; # reset all X variables
reset 'a-z'; # reset lower case variables
reset; # just reset ?? searches
-Resetting "A-Z" is not recommended since you'll wipe out your
-ARGV and ENV arrays. Only resets package variables--lexical variables
+Resetting "A-Z" is not recommended because you'll wipe out your
+ARGV and ENV arrays. Resets only package variables--lexical variables
are unaffected, but they clean themselves up on scope exit anyway,
so you'll probably want to use them instead. See L</my>.
=item rmdir FILENAME
+=item rmdir
+
Deletes the directory specified by FILENAME if it is empty. If it
-succeeds it returns 1, otherwise it returns 0 and sets $! (errno). If
+succeeds it returns 1, otherwise it returns 0 and sets C<$!> (errno). If
FILENAME is omitted, uses $_.
=item s///
seek() to reset things. First the simple trick listed above to clear the
filepointer. The seek() doesn't change the current position, but it
I<does> clear the end-of-file condition on the handle, so that the next
-C<E<lt>FILEE<gt>> makes Perl try again to read something. Hopefully.
+C<E<lt>FILEE<gt>> makes Perl try again to read something. We hope.
If that doesn't work (some stdios are particularly cantankerous), then
you may need something more like this:
=item select RBITS,WBITS,EBITS,TIMEOUT
-This calls the select(2) system call with the bitmasks specified, which
+This calls the select(2) system call with the bit masks specified, which
can be constructed using fileno() and vec(), along these lines:
$rin = $win = $ein = '';
Most systems do not both to return anything useful in $timeleft, so
calling select() in a scalar context just returns $nfound.
-Any of the bitmasks can also be undef. The timeout, if specified, is
+Any of the bit masks can also be undef. The timeout, if specified, is
in seconds, which may be fractional. Note: not all implementations are
capable of returning the $timeleft. If not, they always return
$timeleft equal to the supplied $timeout.
-You can effect a 250-millisecond sleep this way:
+You can effect a sleep of 250 milliseconds this way:
select(undef, undef, undef, 0.25);
-B<WARNING>: Do not attempt to mix buffered I/O (like read() or <FH>)
+B<WARNING>: Do not attempt to mix buffered I/O (like read() or E<lt>FHE<gt>)
with select(). You have to use sysread() instead.
=item semctl ID,SEMNUM,CMD,ARG
Sets the current process group for the specified PID, 0 for the current
process. Will produce a fatal error if used on a machine that doesn't
-implement setpgrp(2). If the arguments are ommitted, it defaults to
+implement setpgrp(2). If the arguments are omitted, it defaults to
0,0. Note that the POSIX version of setpgrp() does not accept any
arguments, so only setpgrp 0,0 is portable.
=item sin EXPR
+=item sin
+
Returns the sine of EXPR (expressed in radians). If EXPR is omitted,
returns sine of $_.
Causes the script to sleep for EXPR seconds, or forever if no EXPR.
May be interrupted by sending the process a SIGALRM. Returns the
number of seconds actually slept. You probably cannot mix alarm() and
-sleep() calls, since sleep() is often implemented using alarm().
+sleep() calls, because sleep() is often implemented using 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
in standard string comparison order. If SUBNAME is specified, it
gives the name of a subroutine that returns an integer less than, equal
to, or greater than 0, depending on how the elements of the array are
-to be ordered. (The <=> and cmp operators are extremely useful in such
+to be ordered. (The E<lt>=E<gt> and cmp operators are extremely useful in such
routines.) SUBNAME may be a scalar variable name, in which case the
value provides the name of the subroutine to use. In place of a
SUBNAME, you can provide a BLOCK as an anonymous, in-line sort
@sortedclass = sort byage @class;
# this sorts the %age associative arrays by value
- # instead of key using an inline function
+ # instead of key using an in-line function
@eldest = sort { $age{$b} <=> $age{$a} } keys %age;
sub backwards { $b cmp $a; }
$a->[2] cmp $b->[2]
} map { [$_, /=(\d+)/, uc($_)] } @old;
-If you're and using strict, you I<MUST NOT> declare $a
+If you're using strict, you I<MUST NOT> declare $a
and $b as lexicals. They are package globals. That means
if you're in the C<main> package, it's
@articles = sort {$FooPack::b <=> $FooPack::a} @files;
+The comparison function is required to behave. If it returns
+inconsistent results (sometimes saying $x[1] is less than $x[2] and
+sometimes saying the opposite, for example) the Perl interpreter will
+probably crash and dump core. This is entirely due to and dependent
+upon your system's qsort(3) library routine; this routine often avoids
+sanity checks in the interest of speed.
+
=item splice ARRAY,OFFSET,LENGTH,LIST
=item splice ARRAY,OFFSET,LENGTH
replaces them with the elements of LIST, if any. Returns the elements
removed from the array. The array grows or shrinks as necessary. If
LENGTH is omitted, removes everything from OFFSET onward. The
-following equivalencies hold (assuming $[ == 0):
+following equivalencies hold (assuming C<$[ == 0>):
push(@a,$x,$y) splice(@a,$#a+1,0,$x,$y)
pop(@a) splice(@a,-1)
produces the output 'h:i:t:h:e:r:e'.
-The LIMIT parameter can be used to partially split a line
+The LIMIT parameter can be used to split a line partially
($login, $passwd, $remainder) = split(/:/, $_, 3);
=item sqrt EXPR
+=item sqrt
+
Return the square root of EXPR. If EXPR is omitted, returns square
root of $_.
=item srand EXPR
Sets the random number seed for the C<rand> operator. If EXPR is omitted,
-uses a semirandom value based on the current time and process ID, among
+uses a semi-random value based on the current time and process ID, among
other things. Of course, you'd need something much more random than that for
-cryptographic purposes, since it's easy to guess the current time.
+cryptographic purposes, because it's easy to guess the current time.
Checksumming the compressed output of rapidly changing operating system
status programs is the usual method. Examples are posted regularly to
the comp.security.unix newsgroup.
=item stat EXPR
+=item stat
+
Returns a 13-element array giving the status info for a file, either the
-file opened via FILEHANDLE, or named by EXPR. Returns a null list if
-the stat fails. Typically used as follows:
+file opened via FILEHANDLE, or named by EXPR. If EXPR is omitted, it
+stats $_. Returns a null list if the stat fails. Typically used as
+follows:
+
($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
$atime,$mtime,$ctime,$blksize,$blocks)
mode file mode (type and permissions)
nlink number of (hard) links to the file
uid numeric user ID of file's owner
- gid numer group ID of file's owner
+ gid numeric group ID of file's owner
rdev the device identifier (special files only)
size total size of file, in bytes
atime last access time since the epoch
mtime last modify time since the epoch
ctime inode change time (NOT creation type!) since the epoch
- blksize preferred blocksize for file system I/O
+ blksize preferred block size for file system I/O
blocks actual number of blocks allocated
(The epoch was at 00:00 January 1, 1970 GMT.)
print "$file is executable NFS file\n";
}
-(This only works on machines for which the device number is negative under NFS.)
+(This works on machines only for which the device number is negative under NFS.)
=item study SCALAR
=item study
-Takes extra time to study SCALAR ($_ if unspecified) in anticipation of
+Takes extra time to study SCALAR (C<$_> if unspecified) in anticipation of
doing many pattern matches on the string before it is next modified.
This may or may not save time, depending on the nature and number of
patterns you are searching on, and on the distribution of character
frequencies in the string to be searched--you probably want to compare
-runtimes with and without it to see which runs faster. Those loops
+run times with and without it to see which runs faster. Those loops
which scan for many short constant strings (including the constant
parts of more complex patterns) will benefit most. You may have only
one study active at a time--if you study a different scalar the first
avoid recompiling all your patterns all the time. Together with
undefining $/ to input entire files as one record, this can be very
fast, often faster than specialized programs like fgrep(1). The following
-scans a list of files (@files) for a list of words (@words), and prints
+scans a list of files (C<@files>) for a list of words (C<@words>), and prints
out the names of those files that contain a match:
$search = 'while (<>) { study;';
@ARGV = @files;
undef $/;
eval $search; # this screams
- $/ = "\n"; # put back to normal input delim
+ $/ = "\n"; # put back to normal input delimiter
foreach $file (sort keys(%seen)) {
print $file, "\n";
}
require 'syscall.ph'; # may need to run h2ph
syscall(&SYS_write, fileno(STDOUT), "hi there\n", 9);
-Note that Perl only supports passing of up to 14 arguments to your system call,
+Note that Perl supports passing of up to only 14 arguments to your system call,
which in practice should usually suffice.
=item sysopen FILEHANDLE,FILENAME,MODE
specified FILEHANDLE, using the system call read(2). It bypasses
stdio, so mixing this with other kinds of reads may cause confusion.
Returns the number of bytes actually read, or undef if there was an
-error. SCALAR will be grown or shrunk to the length actually read. An
-OFFSET may be specified to place the read data at some other place than
-the beginning of the string.
+error. SCALAR will be grown or shrunk so that the last byte actually
+read is the last byte of the scalar after the read.
+
+An OFFSET may be specified to place the read data at some place in the
+string other than the beginning. A negative OFFSET specifies
+placement at that many bytes counting backwards from the end of the
+string. A positive OFFSET greater than the length of SCALAR results
+in the string being padded to the required size with "\0" bytes before
+the result of the read is appended.
=item system LIST
arguments. The return value is the exit status of the program as
returned by the wait() call. To get the actual exit value divide by
256. See also L</exec>. This is I<NOT> what you want to use to capture
-the output from a command, for that you should merely use backticks, as
+the output from a command, for that you should use merely back-ticks, as
described in L<perlop/"`STRING`">.
=item syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET
Attempts to write LENGTH bytes of data from variable SCALAR to the
specified FILEHANDLE, using the system call write(2). It bypasses
stdio, so mixing this with prints may cause confusion. Returns the
-number of bytes actually written, or undef if there was an error. An
-OFFSET may be specified to get the write data from some other place than
-the beginning of the string.
+number of bytes actually written, or undef if there was an error.
+If the length is greater than the available data, only as much data as
+is available will be written.
+
+An OFFSET may be specified to write the data from some part of the
+string other than the beginning. A negative OFFSET specifies writing
+from that many bytes counting backwards from the end of the string.
=item tell FILEHANDLE
=item uc EXPR
+=item uc
+
Returns an uppercased version of EXPR. This is the internal function
implementing the \U escape in double-quoted strings.
Should respect any POSIX setlocale() settings.
+If EXPR is omitted, uses $_.
+
=item ucfirst EXPR
+=item ucfirst
+
Returns the value of EXPR with the first character uppercased. This is
the internal function implementing the \u escape in double-quoted strings.
Should respect any POSIX setlocale() settings.
+If EXPR is omitted, uses $_.
+
=item umask EXPR
=item umask
Sets the umask for the process and returns the old one. If EXPR is
-omitted, merely returns current umask.
+omitted, returns merely the current umask.
=item undef EXPR
=item undef
-Undefines the value of EXPR, which must be an lvalue. Use only on a
+Undefines the value of EXPR, which must be an lvalue. Use on only a
scalar value, an entire array, or a subroutine name (using "&"). (Using undef()
will probably not do what you expect on most predefined variables or
DBM list values, so don't do that.) Always returns the undefined value. You can omit
=item unlink LIST
+=item unlink
+
Deletes a list of files. Returns the number of files successfully
deleted.
met, be warned that unlinking a directory can inflict damage on your
filesystem. Use rmdir instead.
+If LIST is omitted, uses $_.
+
=item unpack TEMPLATE,EXPR
Unpack does the reverse of pack: it takes a string representing a
structure and expands it out into a list value, returning the array
-value. (In a scalar context, it merely returns the first value
+value. (In a scalar context, it returns merely the first value
produced.) The TEMPLATE has the same format as in the pack function.
Here's a subroutine that does substring:
sub ordinal { unpack("c",$_[0]); } # same as ord()
-In addition, you may prefix a field with a %<number> to indicate that
-you want a <number>-bit checksum of the items instead of the items
+In addition, you may prefix a field with a %E<lt>numberE<gt> to indicate that
+you want a E<lt>numberE<gt>-bit checksum of the items instead of the items
themselves. Default is a 16-bit checksum. For example, the following
computes the same number as the System V sum program:
features back into the current package. The module can implement its
import method any way it likes, though most modules just choose to
derive their import method via inheritance from the Exporter class that
-is defined in the Exporter module. See L<Exporter>.
+is defined in the Exporter module. See L<Exporter>. If no import
+method can be found then the error is currently silently ignored. This
+may change to a fatal error in a future version.
If you don't want your namespace altered, explicitly supply an empty list:
use strict qw(subs vars refs);
use subs qw(afunc blurfl);
-These pseudomodules import semantics into the current block scope, unlike
+These pseudo-modules import semantics into the current block scope, unlike
ordinary modules, which import symbols into the current package (which are
effective through the end of the file).
There's a corresponding "no" command that unimports meanings imported
-by use, i.e. it calls C<unimport Module LIST> instead of C<import>.
+by use, i.e., it calls C<unimport Module LIST> instead of C<import>.
no integer;
no strict 'refs';
+If no unimport method can be found the call fails with a fatal error.
+
See L<perlmod> for a list of standard modules and pragmas.
=item utime LIST
=item vec EXPR,OFFSET,BITS
Treats the string in EXPR as a vector of unsigned integers, and
-returns the value of the bitfield specified by OFFSET. BITS specifies
+returns the value of the bit field specified by OFFSET. BITS specifies
the number of bits that are reserved for each entry in the bit
vector. This must be a power of two from 1 to 32. vec() may also be
-assigned to, in which case parens are needed to give the expression
+assigned to, in which case parentheses are needed to give the expression
the correct precedence as in
vec($image, $max_x * $x + $y, 8) = 3;
Waits for a child process to terminate and returns the pid of the
deceased process, or -1 if there are no child processes. The status is
-returned in $?.
+returned in C<$?>.
=item waitpid PID,FLAGS
Waits for a particular child process to terminate and returns the pid
of the deceased process, or -1 if there is no such child process. The
-status is returned in $?. If you say
+status is returned in C<$?>. If you say
use POSIX ":wait_h";
...
waitpid(-1,&WNOHANG);
then you can do a non-blocking wait for any process. Non-blocking wait
-is only available on machines supporting either the waitpid(2) or
+is available on machines supporting either the waitpid(2) or
wait4(2) system calls. However, waiting for a particular pid with
FLAGS of 0 is implemented everywhere. (Perl emulates the system call
by remembering the status values of processes that have exited but have
using the format associated with that file. By default the format for
a file is the one having the same name is the filehandle, but the
format for the current output channel (see the select() function) may be set
-explicitly by assigning the name of the format to the $~ variable.
+explicitly by assigning the name of the format to the C<$~> variable.
Top of form processing is handled automatically: if there is
insufficient room on the current page for the formatted record, the
is used to format the new page header, and then the record is written.
By default the top-of-page format is the name of the filehandle with
"_TOP" appended, but it may be dynamically set to the format of your
-choice by assigning the name to the $^ variable while the filehandle is
+choice by assigning the name to the C<$^> variable while the filehandle is
selected. The number of lines remaining on the current page is in
-variable $-, which can be set to 0 to force a new page.
+variable C<$->, which can be set to 0 to force a new page.
If FILEHANDLE is unspecified, output goes to the current default output
channel, which starts out as STDOUT but may be changed by the
projects / p5sagit/p5-mst-13.2.git / blobdiff