=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<umask>, C<unlink>, C<utime>
+C<ioctl>, C<link>, C<lstat>, C<mkdir>, C<open>, C<opendir>,
+C<readlink>, C<rename>, C<rmdir>, C<stat>, C<symlink>, 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>
+C<caller>, C<continue>, C<die>, C<do>, C<dump>, C<else>, C<elsif>,
+C<eval>, C<exit>, C<for>, C<foreach>, C<goto>, C<if>, C<last>,
+C<next>, C<redo>, C<return>, C<sub>, C<unless>, C<wantarray>,
+C<while>, C<until>
=item Keywords related to scoping
=back
+=head2 Portability
+
+Perl was born in UNIX and therefore it can access all the common UNIX
+system calls. In non-UNIX environments the functionality of many
+UNIX system calls may not be available or the details of the available
+functionality may be slightly different. 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<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>,
+C<kill>, C<link>, C<lstat>, C<msgctl>, C<msgget>, C<msgrcv>,
+C<msgsnd>, C<open>, C<pipe>, C<readlink>, 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<socketpair>, C<stat>, C<symlink>, C<syscall>,
+C<sysopen>, C<system>, C<times>, C<truncate>, C<umask>, 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
-A Same for access time.
-C Same for inode change time.
-The interpretation of the file permission operators C<-r>, C<-R>, C<-w>,
-C<-W>, C<-x>, and C<-X> is based solely on the mode of the file and the
-uids and gids of the user. There may be other reasons you can't actually
-read, write, or execute the file, such as AFS access control lists. Also note that, for the superuser,
-C<-r>, C<-R>, C<-w>, and C<-W> always return C<1>, and C<-x> and C<-X> return
-C<1> if any execute bit is set in the mode. Scripts run by the superuser may
-thus need to do a C<stat()> to determine the actual mode of the
-file, or temporarily set the uid to something else.
-
Example:
while (<>) {
#...
}
+The interpretation of the file permission operators C<-r>, C<-R>,
+C<-w>, C<-W>, C<-x>, and C<-X> is by default based solely on the mode
+of the file and the uids and gids of the user. There may be other
+reasons you can't actually read, write, or execute the file. Such
+reasons may be for example network filesystem access controls, ACLs
+(access control lists), read-only filesystems, and unrecognized
+executable formats.
+
+Also note that, for the superuser on the local filesystems, 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() to determine the actual mode of the file,
+or temporarily set the uid to something else.
+
+If you are using ACLs, there is a pragma called C<filetest> that may
+produce more accurate results than the bare stat() mode bits.
+
+When under the C<use filetest 'access'> the above-mentioned filetests
+will test whether the permission can (not) be granted using the
+access() family of system calls. Also note that the C<-x> and C<-X> may
+under this pragma return true even if there are no execute permission
+bits set (nor any extra execute permission ACLs). This strangeness is
+due to the underlying system calls' definitions. Read the
+documentation for the C<filetest> pragma for more information.
+
Note that C<-s/a/b/> does not do a negated substitution. Saying
C<-exp($foo)> still works as expected, however--only single letters
following a minus are interpreted as file tests.
might be inherited by a derived class. See L<perltoot> and L<perlobj>
for more about the blessing (and blessings) of objects.
+Creating objects in lowercased CLASSNAMEs should be avoided. Such
+namespaces should be considered reserved for Perl pragmata and objects
+that may be created to implement internal operations.
+
+See L<perlmod/"Perl Modules">.
+
=item caller EXPR
=item caller
=item continue BLOCK
Actually a flow control statement rather than a function. If there is a
-C<continue> BLOCK attached to a BLOCK (typically in a C<while> or
-C<foreach>), it is always executed just before the conditional is about to
-be evaluated again, just like the third part of a C<for> loop in C. Thus
+C<continue> BLOCK attached to a BLOCK (typically in a L</while> or
+L</foreach>), it is always executed just before the conditional is about to
+be evaluated again, just like the third part of a L</for> loop in C. Thus
it can be used to increment a loop variable, even when the loop has been
continued via the C<next> statement (which is similar to the C C<continue>
statement).
-C<last>, C<next>, or C<redo> may appear within a C<continue>
+L</last>, L</next>, or L</redo> may appear within a C<continue>
block. C<last> and C<redo> will behave as if they had been executed within
the main block. So will C<next>, but since it will execute a C<continue>
block, it may be more entertaining.
empty one, logically enough. In that case, C<next> goes directly back
to check the condition at the top of the loop.
+See also L<perlsyn>.
+
=item cos EXPR
Returns the cosine of EXPR (expressed in radians). If EXPR is omitted,
Not really a function. Returns the value of the last command in the
sequence of commands indicated by BLOCK. When modified by a loop
-modifier, executes the BLOCK once before testing the loop condition.
-(On other statements the loop modifiers test the conditional first.)
+modifier such as L</while> or L</until>, executes the BLOCK once
+before testing the loop condition. (On other statements the loop
+modifiers test the conditional first.)
C<do BLOCK> does I<not> count as a loop, so the loop control statements
-C<next>, C<last> or C<redo> cannot be used to leave or restart the block.
+L</next>, L</last> or L</redo> cannot be used to leave or restart the block.
=item do SUBROUTINE(LIST)
false; you may wish to avoid constructs like C<while ($k = each %foo) {}>
for this reason.)
-Entries are returned in an apparently random order. When the hash is
-entirely read, a null array is returned in list context (which when
-assigned produces a FALSE (C<0>) value), and C<undef> in
+Entries are returned in an apparently random order. The actual random
+order is subject to change in future versions of perl, but it is guaranteed
+to be in the same order as either the C<keys()> or C<values()> function
+would produce on the same (unmodified) hash.
+
+When the hash is entirely read, a null array is returned in list context
+(which when assigned produces a FALSE (C<0>) value), and C<undef> in
scalar context. The next call to C<each()> after that will start iterating
again. There is a single iterator for each hash, shared by all C<each()>,
C<keys()>, and C<values()> function calls in the program; it can be reset by
print "$key=$value\n";
}
-See also C<keys()> and C<values()>.
+See also C<keys()>, C<values()> and C<sort()>.
+
+=item else BLOCK
+
+=item elsif (EXPR) BLOCK
+
+See L</if>.
=item eof FILEHANDLE
See also L<DB_File> for other flock() examples.
+=item for (INITIAL; WHILE; EACH) BLOCK
+
+Do INITIAL, enter BLOCK while EXPR is true, at the end of each round
+do EACH. For example:
+
+ for ($i = 0, $j = 0; $i < 10; $i++) {
+ if ($i % 3 == 0) { $j++ }
+ print "i = $i, j = $j\n";
+ }
+
+See L<perlsyn> for more details. See also L</foreach>, a twin of
+C<for>, L</while> and L</until>, close cousins of L<for>, and
+L</last>, L</next>, and L</redo> for additional control flow.
+
+=item foreach LOOPVAR (LIST) BLOCK
+
+Enter BLOCK as LOOPVAR set in turn to each element of LIST.
+For example:
+
+ foreach $rolling (@stones) { print "rolling $stone\n" }
+
+ foreach my $file (@files) { print "file $file\n" }
+
+The LOOPVAR is optional and defaults to C<$_>. If the elements are
+modifiable (as opposed to constants or tied variables) you can modify them.
+
+ foreach (@words) { tr/abc/xyz/ }
+
+See L<perlsyn> for more details. See also L</for>, a twin of
+C<foreach>, L</while> and L</until>, close cousins of L<for>, and
+L</last>, L</next>, and L</redo> for additional control flow.
+
=item fork
Does a fork(2) system call. Returns the child pid to the parent process,
print hex '0xAf'; # prints '175'
print hex 'aF'; # same
+=item if (EXPR) BLOCK
+
+=item if (EXPR) BLOCK else BLOCK2
+
+=item if (EXPR) BLOCK elsif (EXPR2) BLOCK2
+
+Enter BLOCKs conditionally. The first EXPR to return true
+causes the corresponding BLOCK to be entered, or, in the case
+of C<else>, the fall-through default BLOCK.
+
+Take notice: Perl wants BLOCKS, expressions (like e.g. in C, C++, or
+Pascal) won't do.
+
+See L<perlsyn> for more details. See also C<unless>.
+
=item import
There is no builtin C<import()> function. It is just an ordinary
Returns a list consisting of all the keys of the named hash. (In a
scalar context, returns the number of keys.) The keys are returned in
-an apparently random order, but it is the same order as either the
-C<values()> or C<each()> function produces (given that the hash has not been
-modified). As a side effect, it resets HASH's iterator.
+an apparently random order. The actual random order is subject to
+change in future versions of perl, but it is guaranteed to be the same
+order as either the C<values()> or C<each()> function produces (given
+that the hash has not been modified). As a side effect, it resets
+HASH's iterator.
Here is yet another way to print your environment:
keys %hash = 200;
-then C<%hash> will have at least 200 buckets allocated for it--256 of them, in fact, since
-it rounds up to the next power of two. These
+then C<%hash> will have at least 200 buckets allocated for it--256 of them,
+in fact, since it rounds up to the next power of two. 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).
+See also C<each()>, C<values()> and C<sort()>.
+
=item kill LIST
Sends a signal to a list of processes. The first element of
C<last> cannot be used to exit a block which returns a value such as
C<eval {}>, C<sub {}> or C<do {}>.
-See also L</continue> for an illustration of how C<last>, C<next>, and
-C<redo> work.
+See also L</continue> for an illustration of how C<last>, L</next>, and
+L</redo> work.
+
+See also L<perlsyn>.
=item lc EXPR
=item mkdir FILENAME,MODE
-Creates the directory specified by FILENAME, with permissions specified
-by MODE (as modified by umask). If it succeeds it returns TRUE, otherwise
-it returns FALSE and sets C<$!> (errno).
+Creates the directory specified by FILENAME, with permissions
+specified by MODE (as modified by C<umask>). If it succeeds it
+returns TRUE, otherwise it returns FALSE and sets C<$!> (errno).
+
+In general, it is better to create directories with permissive MODEs,
+and let the user modify that with their C<umask>, than it is to supply
+a restrictive MODE and give the user no way to be more permissive.
+The exceptions to this rule are when the file or directory should be
+kept private (mail files, for instance). The perlfunc(1) entry on
+C<umask> discusses the choice of MODE in more detail.
=item msgctl ID,CMD,ARG
C<next> cannot be used to exit a block which returns a value such as
C<eval {}>, C<sub {}> or C<do {}>.
-See also L</continue> for an illustration of how C<last>, C<next>, and
-C<redo> work.
+See also L</continue> for an illustration of how L</last>, C<next>, and
+L</redo> work.
+
+See also L<perlsyn>.
=item no Module LIST
always preferred for read/write updates--the C<'+E<gt>'> mode would clobber the
file first. You can't usually use either read-write mode for updating
textfiles, since they have variable length records. See the B<-i>
-switch in L<perlrun> for a better approach.
+switch in L<perlrun> for a better approach. The file is created with
+permissions of C<0666> modified by the process' C<umask> value.
The prefix and the filename may be separated with spaces.
These various prefixes correspond to the fopen(3) modes of C<'r'>, C<'r+'>, C<'w'>,
NOTE: On any operation that may do a fork, any unflushed buffers remain
unflushed in both processes, which means you may need to set C<$|> to
-avoid duplicate output.
+avoid duplicate output. On systems that support a close-on-exec flag on
+files, the flag will be set for the newly opened file descriptor as
+determined by the value of $^F. See L<perlvar/$^F>.
Closing any piped filehandle causes the parent process to wait for the
child to finish, and returns the status value in C<$?>.
(These 'shorts' and 'longs' are _exactly_ 16 bits and
_exactly_ 32 bits, respectively.)
+ q A signed quad (64-bit) value.
+ Q An unsigned quad value.
+ (Available only if your system supports 64-bit integer values
+ _and_ if Perl has been compiled to support those.
+ Causes a fatal error otherwise.)
+
f A single-precision float in the native format.
d A double-precision float in the native format.
See L<IPC::Open2>, L<IPC::Open3>, and L<perlipc/"Bidirectional Communication">
for examples of such things.
+On systems that support a close-on-exec flag on files, the flag will be set
+for the newly opened file descriptors as determined by the value of $^F.
+See L<perlvar/$^F>.
+
=item pop ARRAY
=item pop
=item qw/STRING/
-Generalized quotes. See L<perlop>.
+Generalized quotes. See L<perlop/"Regexp Quote-Like Operators">.
=item quotemeta EXPR
=item redo
The C<redo> command restarts the loop block without evaluating the
-conditional again. The C<continue> block, if any, is not executed. If
+conditional again. The L</continue> block, if any, is not executed. If
the LABEL is omitted, the command refers to the innermost enclosing
loop. This command is normally used by programs that want to lie to
themselves about what was just input:
C<redo> cannot be used to retry a block which returns a value such as
C<eval {}>, C<sub {}> or C<do {}>.
-See also L</continue> for an illustration of how C<last>, C<next>, and
+See also L</continue> for an illustration of how L</last>, L</next>, and
C<redo> work.
+See also L<perlsyn>.
+
=item ref EXPR
=item ref
=item srand
Sets the random number seed for the C<rand()> operator. If EXPR is
-omitted, uses a semi-random value based on the current time and process
+omitted, uses a semi-random value supplied by the kernel (if it supports
+the F</dev/urandom> device) or based on the current time and process
ID, among other things. In versions of Perl prior to 5.004 the default
seed was just the current C<time()>. This isn't a particularly good seed,
so many old programs supply their own seed value (often C<time ^ $$> or
For historical reasons, some values work on almost every system
supported by perl: zero means read-only, one means write-only, and two
means read/write. We know that these values do I<not> work under
-OS/390 Unix and on the Macintosh; you probably don't want to use them
-in new code.
+OS/390 & VM/ESA Unix and on the Macintosh; you probably don't want to
+use them in new code.
If the file named by FILENAME does not exist and the C<open()> call creates
it (typically because MODE includes the C<O_CREAT> flag), then the value of
PERMS specifies the permissions of the newly created file. If you omit
the PERMS argument to C<sysopen()>, Perl uses the octal value C<0666>.
These permission values need to be in octal, and are modified by your
-process's current C<umask>. The C<umask> value is a number representing
-disabled permissions bits--if your C<umask> were C<027> (group can't write;
-others can't read, write, or execute), then passing C<sysopen()> C<0666> would
-create a file with mode C<0640> (C<0666 &~ 027> is C<0640>).
-
-If you find this C<umask()> talk confusing, here's some advice: supply a
-creation mode of C<0666> for regular files and one of C<0777> for directories
-(in C<mkdir()>) and executable files. This gives users the freedom of
-choice: if they want protected files, they might choose process umasks
-of C<022>, C<027>, or even the particularly antisocial mask of C<077>. Programs
-should rarely if ever make policy decisions better left to the user.
-The exception to this is when writing files that should be kept private:
-mail files, web browser cookies, I<.rhosts> files, and so on. In short,
-seldom if ever use C<0644> as argument to C<sysopen()> because that takes
-away the user's option to have a more permissive umask. Better to omit it.
+process's current C<umask>.
+
+Seldom if ever use C<0644> as argument to C<sysopen()> because that
+takes away the user's option to have a more permissive umask. Better
+to omit it. See the perlfunc(1) entry on C<umask> for more on this.
The C<IO::File> module provides a more object-oriented approach, if you're
into that kind of thing.
=item sysread FILEHANDLE,SCALAR,LENGTH
Attempts to read LENGTH bytes of data into variable SCALAR from the
-specified FILEHANDLE, using the system call read(2). It bypasses
-stdio, so mixing this with other kinds of reads, C<print()>, C<write()>,
-C<seek()>, or C<tell()> can cause confusion because stdio usually buffers
-data. Returns the number of bytes actually read, C<0> at end of file,
-or undef if there was an error. SCALAR will be grown or shrunk so that
-the last byte actually read is the last byte of the scalar after the read.
+specified FILEHANDLE, using the system call read(2). It bypasses stdio,
+so mixing this with other kinds of reads, C<print()>, C<write()>,
+C<seek()>, C<tell()>, or C<eof()> can cause confusion because stdio
+usually buffers data. Returns the number of bytes actually read, C<0>
+at end of file, or undef if there was an 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
Sets FILEHANDLE's system position using the system call lseek(2). It
bypasses stdio, so mixing this with reads (other than C<sysread()>),
-C<print()>, C<write()>, C<seek()>, or C<tell()> may cause confusion. FILEHANDLE may
-be an expression whose value gives the name of the filehandle. The
-values for WHENCE are C<0> to set the new position to POSITION, C<1> to set
-the it to the current position plus POSITION, and C<2> to set it to EOF
-plus POSITION (typically negative). For WHENCE, you may use the
-constants C<SEEK_SET>, C<SEEK_CUR>, and C<SEEK_END> from either the C<IO::Seekable>
-or the POSIX module.
+C<print()>, C<write()>, C<seek()>, C<tell()>, or C<eof()> may cause
+confusion. FILEHANDLE may be an expression whose value gives the name
+of the filehandle. The values for WHENCE are C<0> to set the new
+position to POSITION, C<1> to set the it to the current position plus
+POSITION, and C<2> to set it to EOF plus POSITION (typically negative).
+For WHENCE, you may use the constants C<SEEK_SET>, C<SEEK_CUR>, and
+C<SEEK_END> from either the C<IO::Seekable> or the POSIX module.
Returns the new position, or the undefined value on failure. A position
of zero is returned as the string "C<0> but true"; thus C<sysseek()> returns
=item syswrite FILEHANDLE,SCALAR,LENGTH
+=item syswrite FILEHANDLE,SCALAR
+
Attempts to write LENGTH bytes of data from variable SCALAR to the
-specified FILEHANDLE, using the system call write(2). It bypasses
+specified FILEHANDLE, using the system call write(2). If LENGTH is
+not specified, writes whole SCALAR. It bypasses
stdio, so mixing this with reads (other than C<sysread())>, C<print()>,
-C<write()>, C<seek()>, or C<tell()> may cause confusion because stdio usually
-buffers data. Returns the number of bytes actually written, or C<undef>
-if there was an error. If the LENGTH is greater than the available
-data in the SCALAR after the OFFSET, only as much data as is available
-will be written.
+C<write()>, C<seek()>, C<tell()>, or C<eof()> may cause confusion
+because stdio usually buffers data. Returns the number of bytes
+actually written, or C<undef> if there was an error. If the LENGTH is
+greater than the available data in the SCALAR after the OFFSET, 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
implementation for the variable. VARIABLE is the name of the variable
to be enchanted. CLASSNAME is the name of a class implementing objects
of correct type. Any additional arguments are passed to the "C<new()>"
-method of the class (meaning C<TIESCALAR>, C<TIEARRAY>, or C<TIEHASH>).
-Typically these are arguments such as might be passed to the C<dbm_open()>
-function of C. The object returned by the "C<new()>" method is also
-returned by the C<tie()> function, which would be useful if you want to
-access other methods in CLASSNAME.
+method of the class (meaning C<TIESCALAR>, C<TIEHANDLE>, C<TIEARRAY>,
+or C<TIEHASH>). Typically these are arguments such as might be passed
+to the C<dbm_open()> function of C. The object returned by the "C<new()>"
+method is also returned by the C<tie()> function, which would be useful
+if you want to access other methods in CLASSNAME.
Note that functions such as C<keys()> and C<values()> may return huge lists
when used on large objects, like DBM files. You may prefer to use the
A class implementing a hash should have the following methods:
TIEHASH classname, LIST
- DESTROY this
FETCH this, key
STORE this, key, value
DELETE this, key
+ CLEAR this
EXISTS this, key
FIRSTKEY this
NEXTKEY this, lastkey
+ DESTROY this
A class implementing an ordinary array should have the following methods:
TIEARRAY classname, LIST
- DESTROY this
FETCH this, key
STORE this, key, value
- [others TBD]
+ FETCHSIZE this
+ STORESIZE this, count
+ CLEAR this
+ PUSH this, LIST
+ POP this
+ SHIFT this
+ UNSHIFT this, LIST
+ SPLICE this, offset, length, LIST
+ EXTEND this, count
+ DESTROY this
+
+A class implementing a file handle should have the following methods:
+
+ TIEHANDLE classname, LIST
+ READ this, scalar, length, offset
+ READLINE this
+ GETC this
+ WRITE this, scalar, length, offset
+ PRINT this, LIST
+ PRINTF this, format, LIST
+ CLOSE this
+ DESTROY this
A class implementing a scalar should have the following methods:
TIESCALAR classname, LIST
- DESTROY this
FETCH this,
STORE this, value
+ DESTROY this
+
+Not all methods indicated above need be implemented. See L<perltie>,
+L<Tie::Hash>, L<Tie::Array>, L<Tie::Scalar> and L<Tie::Handle>.
Unlike C<dbmopen()>, the C<tie()> function will not use or require a module
for you--you need to do that explicitly yourself. See L<DB_File>
Sets the umask for the process to EXPR and returns the previous value.
If EXPR is omitted, merely returns the current umask.
+The Unix permission C<rwxr-x---> is represented as three sets of three
+bits, or three octal digits: C<0750> (the leading 0 indicates octal
+and isn't one of the the digits). The C<umask> value is such a number
+representing disabled permissions bits. The permission (or "mode")
+values you pass C<mkdir> or C<sysopen> are modified by your umask, so
+even if you tell C<sysopen> to create a file with permissions C<0777>,
+if your umask is C<0022> then the file will actually be created with
+permissions C<0755>. If your C<umask> were C<0027> (group can't
+write; others can't read, write, or execute), then passing
+C<sysopen()> C<0666> would create a file with mode C<0640> (C<0666 &~
+027> is C<0640>).
+
+Here's some advice: supply a creation mode of C<0666> for regular
+files (in C<sysopen()>) and one of C<0777> for directories (in
+C<mkdir()>) and executable files. This gives users the freedom of
+choice: if they want protected files, they might choose process umasks
+of C<022>, C<027>, or even the particularly antisocial mask of C<077>.
+Programs should rarely if ever make policy decisions better left to
+the user. The exception to this is when writing files that should be
+kept private: mail files, web browser cookies, I<.rhosts> files, and
+so on.
+
If umask(2) is not implemented on your system and you are trying to
restrict access for I<yourself> (i.e., (EXPR & 0700) > 0), produces a
fatal error at run time. If umask(2) is not implemented and you are
Note that this is a unary operator, not a list operator.
+=item unless (EXPR) BLOCK
+
+The negative counterpart of L</if>. If the EXPR returns false the
+BLOCK is entered.
+
+See also L<perlsyn>.
+
=item unlink LIST
=item unlink
$setbits = unpack("%32b*", $selectmask);
-=item untie VARIABLE
-
-Breaks the binding between a variable and a package. (See C<tie()>.)
-
=item unshift ARRAY,LIST
Does the opposite of a C<shift()>. Or the opposite of a C<push()>,
prepended elements stay in the same order. Use C<reverse()> to do the
reverse.
+=item until (EXPR) BLOCK
+
+=item do BLOCK until (EXPR)
+
+Enter BLOCK until EXPR returns false. The first form may avoid entering
+the BLOCK, the second form enters the BLOCK at least once.
+
+See L</do>, L</while>, and L</for>.
+
+See also L<perlsyn>.
+
+=item untie VARIABLE
+
+Breaks the binding between a variable and a package. (See C<tie()>.)
+
=item use Module LIST
=item use Module
Returns a list consisting of all the values of the named hash. (In a
scalar context, returns the number of values.) The values are
-returned in an apparently random order, but it is the same order as
-either the C<keys()> or C<each()> function would produce on the same hash.
+returned in an apparently random order. The actual random order is
+subject to change in future versions of perl, but it is guaranteed to
+be the same order as either the C<keys()> or C<each()> function would
+produce on the same (unmodified) hash.
+
As a side effect, it resets HASH's iterator. See also C<keys()>, C<each()>,
and C<sort()>.
Waits for a child process to terminate and returns the pid of the
deceased process, or C<-1> if there are no child processes. The status is
-returned in C<$?>.
+returned in C<$?>. Note that a return value of C<-1> could mean that
+child processes are being automatically reaped, as described in L<perlipc>.
=item waitpid PID,FLAGS
by remembering the status values of processes that have exited but have
not been harvested by the Perl script yet.)
-See L<perlipc> for other examples.
+Note that a return value of C<-1> could mean that child processes are being
+automatically reaped. See L<perlipc> for details, and for other examples.
=item wantarray
See L<perlvar> for details on setting C<%SIG> entries, and for more
examples.
+=item while (EXPR) BLOCK
+
+=item do BLOCK while (EXPR)
+
+Enter BLOCK while EXPR is true. The first form may avoid entering the
+BLOCK, the second form enters the BLOCK at least once.
+
+See also L<perlsyn>, L</for>, L</until>, and L</continue>.
+
=item write FILEHANDLE
=item write EXPR
https://perl5.git.perl.org / perl5.git / blobdiff