perl 3.0 patch #14 patch #13, continued

[p5sagit/p5-mst-13.2.git] / perl.man.2

''' Beginning of part 2
''' $Header: perl.man.2,v 3.0.1.4 90/03/12 16:46:02 lwall Locked $
'''
''' $Log:       perl.man.2,v $
''' Revision 3.0.1.4  90/03/12  16:46:02  lwall
''' patch13: documented behavior of @array = /noparens/
''' 
''' Revision 3.0.1.3  90/02/28  17:55:58  lwall
''' patch9: grep now returns number of items matched in scalar context
''' patch9: documented in-place modification capabilites of grep
''' 
''' Revision 3.0.1.2  89/11/17  15:30:16  lwall
''' patch5: fixed some manual typos and indent problems
''' 
''' Revision 3.0.1.1  89/11/11  04:43:10  lwall
''' patch2: made some line breaks depend on troff vs. nroff
''' patch2: example of unshift had args backwards
''' 
''' Revision 3.0  89/10/18  15:21:37  lwall
''' 3.0 baseline
''' 
'''
.PP
Along with the literals and variables mentioned earlier,
the operations in the following section can serve as terms in an expression.
Some of these operations take a LIST as an argument.
Such a list can consist of any combination of scalar arguments or array values;
the array values will be included in the list as if each individual element were
interpolated at that point in the list, forming a longer single-dimensional
array value.
Elements of the LIST should be separated by commas.
If an operation is listed both with and without parentheses around its
arguments, it means you can either use it as a unary operator or
as a function call.
To use it as a function call, the next token on the same line must
be a left parenthesis.
(There may be intervening white space.)
Such a function then has highest precedence, as you would expect from
a function.
If any token other than a left parenthesis follows, then it is a
unary operator, with a precedence depending only on whether it is a LIST
operator or not.
LIST operators have lowest precedence.
All other unary operators have a precedence greater than relational operators
but less than arithmetic operators.
See the section on Precedence.
.Ip "/PATTERN/" 8 4
See m/PATTERN/.
.Ip "?PATTERN?" 8 4
This is just like the /pattern/ search, except that it matches only once between
calls to the
.I reset
operator.
This is a useful optimization when you only want to see the first occurrence of
something in each file of a set of files, for instance.
Only ?? patterns local to the current package are reset.
.Ip "accept(NEWSOCKET,GENERICSOCKET)" 8 2
Does the same thing that the accept system call does.
Returns true if it succeeded, false otherwise.
See example in section on Interprocess Communication.
.Ip "atan2(X,Y)" 8 2
Returns the arctangent of X/Y in the range
.if t \-\(*p to \(*p.
.if n \-PI to PI.
.Ip "bind(SOCKET,NAME)" 8 2
Does the same thing that the bind system call does.
Returns true if it succeeded, false otherwise.
NAME should be a packed address of the proper type for the socket.
See example in section on Interprocess Communication.
.Ip "chdir(EXPR)" 8 2
.Ip "chdir EXPR" 8 2
Changes the working directory to EXPR, if possible.
If EXPR is omitted, changes to home directory.
Returns 1 upon success, 0 otherwise.
See example under
.IR die .
.Ip "chmod(LIST)" 8 2
.Ip "chmod LIST" 8 2
Changes the permissions of a list of files.
The first element of the list must be the numerical mode.
Returns the number of files successfully changed.
.nf

.ne 2
        $cnt = chmod 0755, \'foo\', \'bar\';
        chmod 0755, @executables;

.fi
.Ip "chop(LIST)" 8 7
.Ip "chop(VARIABLE)" 8
.Ip "chop VARIABLE" 8
.Ip "chop" 8
Chops off the last character of a string and returns the character chopped.
It's used primarily to remove the newline from the end of an input record,
but is much more efficient than s/\en// because it neither scans nor copies
the string.
If VARIABLE is omitted, chops $_.
Example:
.nf

.ne 5
        while (<>) {
                chop;   # avoid \en on last field
                @array = split(/:/);
                .\|.\|.
        }

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

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

.fi
If you chop a list, each element is chopped.
Only the value of the last chop is returned.
.Ip "chown(LIST)" 8 2
.Ip "chown LIST" 8 2
Changes the owner (and group) of a list of files.
The first two elements of the list must be the NUMERICAL uid and gid,
in that order.
Returns the number of files successfully changed.
.nf

.ne 2
        $cnt = chown $uid, $gid, \'foo\', \'bar\';
        chown $uid, $gid, @filenames;

.fi
.ne 23
Here's an example of looking up non-numeric uids:
.nf

        print "User: ";
        $user = <STDIN>;
        chop($user);
        print "Files: "
        $pattern = <STDIN>;
        chop($pattern);
.ie t \{\
        open(pass, \'/etc/passwd\') || die "Can't open passwd: $!\en";
'br\}
.el \{\
        open(pass, \'/etc/passwd\')
                || die "Can't open passwd: $!\en";
'br\}
        while (<pass>) {
                ($login,$pass,$uid,$gid) = split(/:/);
                $uid{$login} = $uid;
                $gid{$login} = $gid;
        }
        @ary = <${pattern}>;    # get filenames
        if ($uid{$user} eq \'\') {
                die "$user not in passwd file";
        }
        else {
                chown $uid{$user}, $gid{$user}, @ary;
        }

.fi
.Ip "chroot(FILENAME)" 8 5
.Ip "chroot FILENAME" 8
Does the same as the system call of that name.
If you don't know what it does, don't worry about it.
If FILENAME is omitted, does chroot to $_.
.Ip "close(FILEHANDLE)" 8 5
.Ip "close FILEHANDLE" 8
Closes the file or pipe associated with the file handle.
You don't have to close FILEHANDLE if you are immediately going to
do another open on it, since open will close it for you.
(See
.IR open .)
However, an explicit close on an input file resets the line counter ($.), while
the implicit close done by
.I open
does not.
Also, closing a pipe will wait for the process executing on the pipe to complete,
in case you want to look at the output of the pipe afterwards.
Closing a pipe explicitly also puts the status value of the command into $?.
Example:
.nf

.ne 4
        open(OUTPUT, \'|sort >foo\');   # pipe to sort
        .\|.\|. # print stuff to output
        close OUTPUT;           # wait for sort to finish
        open(INPUT, \'foo\');   # get sort's results

.fi
FILEHANDLE may be an expression whose value gives the real filehandle name.
.Ip "closedir(DIRHANDLE)" 8 5
.Ip "closedir DIRHANDLE" 8
Closes a directory opened by opendir().
.Ip "connect(SOCKET,NAME)" 8 2
Does the same thing that the connect system call does.
Returns true if it succeeded, false otherwise.
NAME should be a package address of the proper type for the socket.
See example in section on Interprocess Communication.
.Ip "cos(EXPR)" 8 6
.Ip "cos EXPR" 8 6
Returns the cosine of EXPR (expressed in radians).
If EXPR is omitted takes cosine of $_.
.Ip "crypt(PLAINTEXT,SALT)" 8 6
Encrypts a string exactly like the crypt() function in the C library.
Useful for checking the password file for lousy passwords.
Only the guys wearing white hats should do this.
.Ip "dbmclose(ASSOC_ARRAY)" 8 6
.Ip "dbmclose ASSOC_ARRAY" 8
Breaks the binding between a dbm file and an associative array.
The values remaining in the associative array are meaningless unless
you happen to want to know what was in the cache for the dbm file.
This function is only useful if you have ndbm.
.Ip "dbmopen(ASSOC,DBNAME,MODE)" 8 6
This binds a dbm or ndbm file to an associative array.
ASSOC is the name of the associative array.
(Unlike normal open, the first argument is NOT a filehandle, even though
it looks like one).
DBNAME is the name of the database (without the .dir or .pag extension).
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 only have one
dbmopen in your program.
If your system has neither dbm nor ndbm, calling dbmopen produces a fatal
error.
.Sp
Values assigned to the associative array prior to the dbmopen are lost.
A certain number of values from the dbm file are cached in memory.
By default this number is 64, but you can increase it by preallocating
that number of garbage entries in the associative array before the dbmopen.
You can flush the cache if necessary with the reset command.
.Sp
If you don't have write access to the dbm file, you can only read
associative array variables, not set them.
If you want to test whether you can write, either use file tests or
try setting a dummy array entry inside an eval, which will trap the error.
.Sp
Note that functions such as keys() and values() may return huge array values
when used on large dbm files.
You may prefer to use the each() function to iterate over large dbm files.
Example:
.nf

.ne 6
        # print out history file offsets
        dbmopen(HIST,'/usr/lib/news/history',0666);
        while (($key,$val) = each %HIST) {
                print $key, ' = ', unpack('L',$val), "\en";
        }
        dbmclose(HIST);

.fi
.Ip "defined(EXPR)" 8 6
.Ip "defined EXPR" 8
Returns a boolean value saying whether the lvalue 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 null string
and a defined null string with operations that might return a real null
string, in particular referencing elements of an array.
You may also check to see if arrays or subroutines exist.
Use on predefined variables is not guaranteed to produce intuitive results.
Examples:
.nf

.ne 7
        print if defined $switch{'D'};
        print "$val\en" while defined($val = pop(@ary));
        die "Can't readlink $sym: $!"
                unless defined($value = readlink $sym);
        eval '@foo = ()' if defined(@foo);
        die "No XYZ package defined" unless defined %_XYZ;
        sub foo { defined &bar ? &bar(@_) : die "No bar"; }

.fi
See also undef.
.Ip "delete $ASSOC{KEY}" 8 6
Deletes the specified value from the specified associative array.
Returns the deleted value, or the undefined value if nothing was deleted.
Deleting from $ENV{} modifies the environment.
Deleting from an array bound to a dbm file deletes the entry from the dbm
file.
.Sp
The following deletes all the values of an associative array:
.nf

.ne 3
        foreach $key (keys %ARRAY) {
                delete $ARRAY{$key};
        }

.fi
(But it would be faster to use the
.I reset
command.
Saying undef %ARRAY is faster yet.)
.Ip "die(LIST)" 8
.Ip "die LIST" 8
Prints the value of LIST to
.I STDERR
and exits with the current value of $!
(errno).
If $! is 0, exits with the value of ($? >> 8) (\`command\` status).
If ($? >> 8) is 0, exits with 255.
Equivalent examples:
.nf

.ne 3
.ie t \{\
        die "Can't cd to spool: $!\en" unless chdir \'/usr/spool/news\';
'br\}
.el \{\
        die "Can't cd to spool: $!\en"
                unless chdir \'/usr/spool/news\';
'br\}

        chdir \'/usr/spool/news\' || die "Can't cd to spool: $!\en" 

.fi
.Sp
If the value of EXPR does not end in a newline, the current script line
number and input line number (if any) are also printed, and a newline is
supplied.
Hint: sometimes appending \*(L", stopped\*(R" to your message will cause it to make
better sense when the string \*(L"at foo line 123\*(R" is appended.
Suppose you are running script \*(L"canasta\*(R".
.nf

.ne 7
        die "/etc/games is no good";
        die "/etc/games is no good, stopped";

produce, respectively

        /etc/games is no good at canasta line 123.
        /etc/games is no good, stopped at canasta line 123.

.fi
See also
.IR exit .
.Ip "do BLOCK" 8 4
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.)
.Ip "do SUBROUTINE (LIST)" 8 3
Executes a SUBROUTINE declared by a
.I sub
declaration, and returns the value
of the last expression evaluated in SUBROUTINE.
If there is no subroutine by that name, produces a fatal error.
(You may use the \*(L"defined\*(R" operator to determine if a subroutine
exists.)
If you pass arrays as part of LIST you may wish to pass the length
of the array in front of each array.
(See the section on subroutines later on.)
SUBROUTINE may be a scalar variable, in which case the variable contains
the name of the subroutine to execute.
The parentheses are required to avoid confusion with the \*(L"do EXPR\*(R"
form.
.Sp
As an alternate form, you may call a subroutine by prefixing the name with
an ampersand: &foo(@args).
If you aren't passing any arguments, you don't have to use parentheses.
If you omit the parentheses, no @_ array is passed to the subroutine.
The & form is also used to specify subroutines to the defined and undef
operators.
.Ip "do EXPR" 8 3
Uses the value of EXPR as a filename and executes the contents of the file
as a
.I perl
script.
Its primary use is to include subroutines from a
.I perl
subroutine library.
.nf

        do \'stat.pl\';

is just like

        eval \`cat stat.pl\`;

.fi
except that it's more efficient, more concise, keeps track of the 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 Predefined Names).
It's the same, however, in that it does reparse the file every time you
call it, so if you are going to use the file inside a loop you might prefer
to use \-P and #include, at the expense of a little more startup time.
(The main problem with #include is that cpp doesn't grok # comments\*(--a
workaround is to use \*(L";#\*(R" for standalone comments.)
Note that the following are NOT equivalent:
.nf

.ne 2
        do $foo;        # eval a file
        do $foo();      # call a subroutine

.fi
.Ip "dump LABEL" 8 6
This causes an immediate core dump.
Primarily this is so that you can use the undump program to turn your
core dump into an executable binary after having initialized all your
variables at the beginning of the program.
When the new binary is executed it will begin by executing a "goto LABEL"
(with all the restrictions that goto suffers).
Think of it as a goto with an intervening core dump and reincarnation.
If LABEL is omitted, restarts the program from the top.
WARNING: any files opened at the time of the dump will NOT be open any more
when the program is reincarnated, with possible resulting confusion on the part
of perl.
See also \-u.
.Sp
Example:
.nf

.ne 16
        #!/usr/bin/perl
        do 'getopt.pl';
        do 'stat.pl';
        %days = (
            'Sun',1,
            'Mon',2,
            'Tue',3,
            'Wed',4,
            'Thu',5,
            'Fri',6,
            'Sat',7);

        dump QUICKSTART if $ARGV[0] eq '-d';

    QUICKSTART:
        do Getopt('f');

.fi
.Ip "each(ASSOC_ARRAY)" 8 6
.Ip "each ASSOC_ARRAY" 8
Returns a 2 element array consisting of the key and value for the next
value of an associative array, so that you can iterate over it.
Entries are returned in an apparently random order.
When the array is entirely read, a null array is returned (which when
assigned produces a FALSE (0) value).
The next call to each() after that will start iterating again.
The iterator can be reset only by reading all the elements from the array.
You must not modify the array while iterating over it.
There is a single iterator for each associative array, shared by all
each(), keys() and values() function calls in the program.
The following prints out your environment like the printenv program, only
in a different order:
.nf

.ne 3
        while (($key,$value) = each %ENV) {
                print "$key=$value\en";
        }

.fi
See also keys() and values().
.Ip "eof(FILEHANDLE)" 8 8
.Ip "eof()" 8
.Ip "eof" 8
Returns 1 if the next read on FILEHANDLE will return end of file, or if
FILEHANDLE is not open.
FILEHANDLE may be an expression whose value gives the real filehandle name.
An eof without an argument returns the eof status for the last file read.
Empty parentheses () may be used to indicate the pseudo file formed of the
files listed on the command line, i.e. eof() is reasonable to use inside
a while (<>) loop to detect the end of only the last file.
Use eof(ARGV) or eof without the parentheses to test EACH file in a while (<>) loop.
Examples:
.nf

.ne 7
        # insert dashes just before last line of last file
        while (<>) {
                if (eof()) {
                        print "\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\en";
                }
                print;
        }

.ne 7
        # reset line numbering on each input file
        while (<>) {
                print "$.\et$_";
                if (eof) {      # Not eof().
                        close(ARGV);
                }
        }

.fi
.Ip "eval(EXPR)" 8 6
.Ip "eval EXPR" 8 6
EXPR is parsed and executed as if it were a little
.I perl
program.
It is executed in the context of the current
.I perl
program, so that
any variable settings, subroutine or format definitions remain afterwards.
The value returned is the value of the last expression evaluated, just
as with subroutines.
If there is a syntax error or runtime error, a null string is returned by
eval, and $@ is set to the error message.
If there was no error, $@ is null.
If EXPR is omitted, evaluates $_.
The final semicolon, if any, may be omitted from the expression.
.Sp
Note that, since eval traps otherwise-fatal errors, it is useful for
determining whether a particular feature
(such as dbmopen or symlink) is implemented.
.Ip "exec(LIST)" 8 8
.Ip "exec LIST" 8 6
If there is more than one argument in LIST, or if LIST is an array with
more than one value,
calls execvp() with the arguments in LIST.
If there is only one scalar argument, the argument is checked for shell metacharacters.
If there are any, the entire argument is passed to \*(L"/bin/sh \-c\*(R" for parsing.
If there are none, the argument is split into words and passed directly to
execvp(), which is more efficient.
Note: exec (and system) do not flush your output buffer, so you may need to
set $| to avoid lost output.
Examples:
.nf

        exec \'/bin/echo\', \'Your arguments are: \', @ARGV;
        exec "sort $outfile | uniq";

.fi
.Sp
If you don't really want to execute the first argument, but want to lie
to the program you are executing about its own name, you can specify
the program you actually want to run by assigning that to a variable and
putting the name of the variable in front of the LIST without a comma.
(This always forces interpretation of the LIST as a multi-valued list, even
if there is only a single scalar in the list.)
Example:
.nf

.ne 2
        $shell = '/bin/csh';
        exec $shell '-sh';              # pretend it's a login shell

.fi
.Ip "exit(EXPR)" 8 6
.Ip "exit EXPR" 8
Evaluates EXPR and exits immediately with that value.
Example:
.nf

.ne 2
        $ans = <STDIN>;
        exit 0 \|if \|$ans \|=~ \|/\|^[Xx]\|/\|;

.fi
See also
.IR die .
If EXPR is omitted, exits with 0 status.
.Ip "exp(EXPR)" 8 3
.Ip "exp EXPR" 8
Returns
.I e
to the power of EXPR.
If EXPR is omitted, gives exp($_).
.Ip "fcntl(FILEHANDLE,FUNCTION,SCALAR)" 8 4
Implements the fcntl(2) function.
You'll probably have to say
.nf

        do "fcntl.h";   # probably /usr/local/lib/perl/fcntl.h

.fi
first to get the correct function definitions.
If fcntl.h doesn't exist or doesn't have the correct definitions
you'll have to roll
your own, based on your C header files such as <sys/fcntl.h>.
(There is a perl script called makelib that comes with the perl kit
which may help you in this.)
Argument processing and value return works just like ioctl below.
Note that fcntl will produce a fatal error if used on a machine that doesn't implement
fcntl(2).
.Ip "fileno(FILEHANDLE)" 8 4
.Ip "fileno FILEHANDLE" 8 4
Returns the file descriptor for a filehandle.
Useful for constructing bitmaps for select().
If FILEHANDLE is an expression, the value is taken as the name of
the filehandle.
.Ip "flock(FILEHANDLE,OPERATION)" 8 4
Calls flock(2) on FILEHANDLE.
See manual page for flock(2) for definition of OPERATION.
Will produce a fatal error if used on a machine that doesn't implement
flock(2).
Here's a mailbox appender for BSD systems.
.nf

.ne 20
        $LOCK_SH = 1;
        $LOCK_EX = 2;
        $LOCK_NB = 4;
        $LOCK_UN = 8;

        sub lock {
            flock(MBOX,$LOCK_EX);
            # and, in case someone appended
            # while we were waiting...
            seek(MBOX, 0, 2);
        }

        sub unlock {
            flock(MBOX,$LOCK_UN);
        }

        open(MBOX, ">>/usr/spool/mail/$USER")
                || die "Can't open mailbox: $!";

        do lock();
        print MBOX $msg,"\en\en";
        do unlock();

.fi
.Ip "fork" 8 4
Does a fork() call.
Returns the child pid to the parent process and 0 to the child process.
Note: unflushed buffers remain unflushed in both processes, which means
you may need to set $| to avoid duplicate output.
.Ip "getc(FILEHANDLE)" 8 4
.Ip "getc FILEHANDLE" 8
.Ip "getc" 8
Returns the next character from the input file attached to FILEHANDLE, or
a null string at EOF.
If FILEHANDLE is omitted, reads from STDIN.
.Ip "getlogin" 8 3
Returns the current login from /etc/utmp, if any.
If null, use getpwuid.

        ($login = getlogin) || (($login) = getpwuid($<));

.Ip "getpeername(SOCKET)" 8 3
Returns the packed sockaddr address of other end of the SOCKET connection.
.nf

.ne 4
        # An internet sockaddr
        $sockaddr = 'S n a4 x8';
        $hersockaddr = getpeername(S);
.ie t \{\
        ($family, $port, $heraddr) = unpack($sockaddr,$hersockaddr);
'br\}
.el \{\
        ($family, $port, $heraddr) =
                        unpack($sockaddr,$hersockaddr);
'br\}

.fi
.Ip "getpgrp(PID)" 8 4
.Ip "getpgrp PID" 8
Returns 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
getpgrp(2).
If EXPR is omitted, returns process group of current process.
.Ip "getppid" 8 4
Returns the process id of the parent process.
.Ip "getpriority(WHICH,WHO)" 8 4
Returns the current priority for a process, a process group, or a user.
(See getpriority(2).)
Will produce a fatal error if used on a machine that doesn't implement
getpriority(2).
.Ip "getpwnam(NAME)" 8
.Ip "getgrnam(NAME)" 8
.Ip "gethostbyname(NAME)" 8
.Ip "getnetbyname(NAME)" 8
.Ip "getprotobyname(NAME)" 8
.Ip "getpwuid(UID)" 8
.Ip "getgrgid(GID)" 8
.Ip "getservbyname(NAME,PROTO)" 8
.Ip "gethostbyaddr(ADDR,ADDRTYPE)" 8
.Ip "getnetbyaddr(ADDR,ADDRTYPE)" 8
.Ip "getprotobynumber(NUMBER)" 8
.Ip "getservbyport(PORT,PROTO)" 8
.Ip "getpwent" 8
.Ip "getgrent" 8
.Ip "gethostent" 8
.Ip "getnetent" 8
.Ip "getprotoent" 8
.Ip "getservent" 8
.Ip "setpwent" 8
.Ip "setgrent" 8
.Ip "sethostent(STAYOPEN)" 8
.Ip "setnetent(STAYOPEN)" 8
.Ip "setprotoent(STAYOPEN)" 8
.Ip "setservent(STAYOPEN)" 8
.Ip "endpwent" 8
.Ip "endgrent" 8
.Ip "endhostent" 8
.Ip "endnetent" 8
.Ip "endprotoent" 8
.Ip "endservent" 8
These routines perform the same functions as their counterparts in the
system library.
The return values from the various get routines are as follows:
.nf

        ($name,$passwd,$uid,$gid,
           $quota,$comment,$gcos,$dir,$shell) = getpw.\|.\|.
        ($name,$passwd,$gid,$members) = getgr.\|.\|.
        ($name,$aliases,$addrtype,$length,@addrs) = gethost.\|.\|.
        ($name,$aliases,$addrtype,$net) = getnet.\|.\|.
        ($name,$aliases,$proto) = getproto.\|.\|.
        ($name,$aliases,$port,$proto) = getserv.\|.\|.

.fi
The $members value returned by getgr.\|.\|. is a space separated list
of the login names of the members of the group.
.Sp
The @addrs value returned by the gethost.\|.\|. functions is a list of the
raw addresses returned by the corresponding system library call.
In the Internet domain, each address is four bytes long and you can unpack
it by saying something like:
.nf

        ($a,$b,$c,$d) = unpack('C4',$addr[0]);

.fi
.Ip "getsockname(SOCKET)" 8 3
Returns the packed sockaddr address of this end of the SOCKET connection.
.nf

.ne 4
        # An internet sockaddr
        $sockaddr = 'S n a4 x8';
        $mysockaddr = getsockname(S);
.ie t \{\
        ($family, $port, $myaddr) = unpack($sockaddr,$mysockaddr);
'br\}
.el \{\
        ($family, $port, $myaddr) =
                        unpack($sockaddr,$mysockaddr);
'br\}

.fi
.Ip "getsockopt(SOCKET,LEVEL,OPTNAME)" 8 3
Returns the socket option requested, or undefined if there is an error.
.Ip "gmtime(EXPR)" 8 4
.Ip "gmtime EXPR" 8
Converts a time as returned by the time function to a 9-element array with
the time analyzed for the Greenwich timezone.
Typically used as follows:
.nf

.ne 3
.ie t \{\
    ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = gmtime(time);
'br\}
.el \{\
    ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
                                                gmtime(time);
'br\}

.fi
All array elements are numeric, and come straight out of a struct tm.
In particular this means that $mon has the range 0.\|.11 and $wday has the
range 0.\|.6.
If EXPR is omitted, does gmtime(time).
.Ip "goto LABEL" 8 6
Finds the statement labeled with LABEL and resumes execution there.
Currently you may only go to statements in the main body of the program
that are not nested inside a do {} construct.
This statement is not implemented very efficiently, and is here only to make
the
.IR sed -to- perl
translator easier.
I may change its semantics at any time, consistent with support for translated
.I sed
scripts.
Use it at your own risk.
Better yet, don't use it at all.
.Ip "grep(EXPR,LIST)" 8 4
Evaluates EXPR for each element of LIST (locally setting $_ to each element)
and returns the array value consisting of those elements for which the
expression evaluated to true.
In a scalar context, returns the number of times the expression was true.
.nf

        @foo = grep(!/^#/, @bar);    # weed out comments

.fi
Note that, since $_ is a reference into the array 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 contains literal values.
.Ip "hex(EXPR)" 8 4
.Ip "hex EXPR" 8
Returns the decimal value of EXPR interpreted as an hex string.
(To interpret strings that might start with 0 or 0x see oct().)
If EXPR is omitted, uses $_.
.Ip "ioctl(FILEHANDLE,FUNCTION,SCALAR)" 8 4
Implements the ioctl(2) function.
You'll probably have to say
.nf

        do "ioctl.h";   # probably /usr/local/lib/perl/ioctl.h

.fi
first to get the correct function definitions.
If ioctl.h doesn't exist or doesn't have the correct definitions
you'll have to roll
your own, based on your C header files such as <sys/ioctl.h>.
(There is a perl script called makelib that comes with the perl kit
which may help you in this.)
SCALAR will be read and/or written depending on the FUNCTION\*(--a pointer
to the string value of SCALAR will be passed as the third argument of
the actual ioctl call.
(If SCALAR has no string value but does have a numeric value, that value
will be passed rather than a pointer to the string value.
To guarantee this to be true, add a 0 to the scalar before using it.)
The pack() and unpack() functions are useful for manipulating the values
of structures used by ioctl().
The following example sets the erase character to DEL.
.nf

.ne 9
        do 'ioctl.h';
        $sgttyb_t = "ccccs";            # 4 chars and a short
        if (ioctl(STDIN,$TIOCGETP,$sgttyb)) {
                @ary = unpack($sgttyb_t,$sgttyb);
                $ary[2] = 127;
                $sgttyb = pack($sgttyb_t,@ary);
                ioctl(STDIN,$TIOCSETP,$sgttyb)
                        || die "Can't ioctl: $!";
        }

.fi
The return value of ioctl (and fcntl) is as follows:
.nf

.ne 4
        if OS returns:\h'|3i'perl returns:
          -1\h'|3i'  undefined value
          0\h'|3i'  string "0 but true"
          anything else\h'|3i'  that number

.fi
Thus perl returns true on success and false on failure, yet you can still
easily determine the actual value returned by the operating system:
.nf

        ($retval = ioctl(...)) || ($retval = -1);
        printf "System returned %d\en", $retval;
.fi
.Ip "index(STR,SUBSTR)" 8 4
Returns the position of the first occurrence of SUBSTR in STR, based at 0, or whatever you've
set the $[ variable to.
If the substring is not found, returns one less than the base, ordinarily \-1.
.Ip "int(EXPR)" 8 4
.Ip "int EXPR" 8
Returns the integer portion of EXPR.
If EXPR is omitted, uses $_.
.Ip "join(EXPR,LIST)" 8 8
.Ip "join(EXPR,ARRAY)" 8
Joins the separate strings of LIST or ARRAY into a single string with fields
separated by the value of EXPR, and returns the string.
Example:
.nf
    
.ie t \{\
    $_ = join(\|\':\', $login,$passwd,$uid,$gid,$gcos,$home,$shell);
'br\}
.el \{\
    $_ = join(\|\':\',
                $login,$passwd,$uid,$gid,$gcos,$home,$shell);
'br\}

.fi
See
.IR split .
.Ip "keys(ASSOC_ARRAY)" 8 6
.Ip "keys ASSOC_ARRAY" 8
Returns a normal array consisting of all the keys of the named associative
array.
The keys are returned in an apparently random order, but it is the same order
as either the values() or each() function produces (given that the associative array
has not been modified).
Here is yet another way to print your environment:
.nf

.ne 5
        @keys = keys %ENV;
        @values = values %ENV;
        while ($#keys >= 0) {
                print pop(keys), \'=\', pop(values), "\en";
        }

or how about sorted by key:

.ne 3
        foreach $key (sort(keys %ENV)) {
                print $key, \'=\', $ENV{$key}, "\en";
        }

.fi
.Ip "kill(LIST)" 8 8
.Ip "kill LIST" 8 2
Sends a signal to a list of processes.
The first element of the list must be the signal to send.
Returns the number of processes successfully signaled.
.nf

        $cnt = kill 1, $child1, $child2;
        kill 9, @goners;

.fi
If the signal is negative, kills process groups instead of processes.
(On System V, a negative \fIprocess\fR number will also kill process groups,
but that's not portable.)
You may use a signal name in quotes.
.Ip "last LABEL" 8 8
.Ip "last" 8
The
.I last
command is like the
.I break
statement in C (as used in loops); it immediately exits the loop in question.
If the LABEL is omitted, the command refers to the innermost enclosing loop.
The
.I continue
block, if any, is not executed:
.nf

.ne 4
        line: while (<STDIN>) {
                last line if /\|^$/;    # exit when done with header
                .\|.\|.
        }

.fi
.Ip "length(EXPR)" 8 4
.Ip "length EXPR" 8
Returns the length in characters of the value of EXPR.
If EXPR is omitted, returns length of $_.
.Ip "link(OLDFILE,NEWFILE)" 8 2
Creates a new filename linked to the old filename.
Returns 1 for success, 0 otherwise.
.Ip "listen(SOCKET,QUEUESIZE)" 8 2
Does the same thing that the listen system call does.
Returns true if it succeeded, false otherwise.
See example in section on Interprocess Communication.
.Ip "local(LIST)" 8 4
Declares the listed variables to be local to the enclosing block,
subroutine, eval or \*(L"do\*(R".
All the listed elements must be legal lvalues.
This operator works by saving the current values of those variables in LIST
on a hidden stack and restoring them upon exiting the block, subroutine or eval.
This means that called subroutines can also reference the local variable,
but not the global one.
The LIST may be assigned to if desired, which allows you to initialize
your local variables.
(If no initializer is given, all scalars are initialized to the null string
and all arrays and associative arrays to the null array.)
Commonly this is used to name the parameters to a subroutine.
Examples:
.nf

.ne 13
        sub RANGEVAL {
                local($min, $max, $thunk) = @_;
                local($result) = \'\';
                local($i);

                # Presumably $thunk makes reference to $i

                for ($i = $min; $i < $max; $i++) {
                        $result .= eval $thunk;
                }

                $result;
        }

.ne 6
        if ($sw eq \'-v\') {
            # init local array with global array
            local(@ARGV) = @ARGV;
            unshift(@ARGV,\'echo\');
            system @ARGV;
        }
        # @ARGV restored

.ne 6
        # temporarily add to digits associative array
        if ($base12) {
                # (NOTE: not claiming this is efficient!)
                local(%digits) = (%digits,'t',10,'e',11);
                do parse_num();
        }

.fi
Note that local() is a run-time command, and so gets executed every time
through a loop, using up more stack storage each time until it's all
released at once when the loop is exited.
.Ip "localtime(EXPR)" 8 4
.Ip "localtime EXPR" 8
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 follows:
.nf

.ne 3
.ie t \{\
    ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(time);
'br\}
.el \{\
    ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
                                                localtime(time);
'br\}

.fi
All array elements are numeric, and come straight out of a struct tm.
In particular this means that $mon has the range 0.\|.11 and $wday has the
range 0.\|.6.
If EXPR is omitted, does localtime(time).
.Ip "log(EXPR)" 8 4
.Ip "log EXPR" 8
Returns logarithm (base
.IR e )
of EXPR.
If EXPR is omitted, returns log of $_.
.Ip "lstat(FILEHANDLE)" 8 6
.Ip "lstat FILEHANDLE" 8
.Ip "lstat(EXPR)" 8
.Ip "lstat SCALARVARIABLE" 8
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.
.Ip "m/PATTERN/io" 8 4
.Ip "/PATTERN/io" 8
Searches a string for a pattern match, and returns true (1) or false (\'\').
If no string is specified via the =~ or !~ operator,
the $_ string is searched.
(The string specified with =~ need not be an lvalue\*(--it may be the result of an expression evaluation, but remember the =~ binds rather tightly.)
See also the section on regular expressions.
.Sp
If / is the delimiter then the initial \*(L'm\*(R' is optional.
With the \*(L'm\*(R' you can use any pair of characters as delimiters.
This is particularly useful for matching Unix path names that contain \*(L'/\*(R'.
If the final delimiter is followed by the optional letter \*(L'i\*(R', the matching is
done in a case-insensitive manner.
PATTERN may contain references to scalar variables, which will be interpolated
(and the pattern recompiled) every time the pattern search is evaluated.
If you want such a pattern to be compiled only once, add an \*(L"o\*(R" after
the trailing delimiter.
This avoids expensive run-time recompilations, and
is useful when the value you are interpolating won't change over the
life of the script.
.Sp
If used in a context that requires an array value, a pattern match returns an
array consisting of the subexpressions matched by the parentheses in the
pattern,
i.e. ($1, $2, $3.\|.\|.).
It does NOT actually set $1, $2, etc. in this case, nor does it set $+, $`, $&
or $'.
If the match fails, a null array is returned.
If the match succeeds, but there were no parentheses, an array value of (1)
is returned.
.Sp
Examples:
.nf

.ne 4
    open(tty, \'/dev/tty\');
    <tty> \|=~ \|/\|^y\|/i \|&& \|do foo(\|);   # do foo if desired

    if (/Version: \|*\|([0\-9.]*\|)\|/\|) { $version = $1; }

    next if m#^/usr/spool/uucp#;

.ne 5
    # poor man's grep
    $arg = shift;
    while (<>) {
            print if /$arg/o;   # compile only once
    }

    if (($F1, $F2, $Etc) = ($foo =~ /^(\eS+)\es+(\eS+)\es*(.*)/))

.fi
This last example splits $foo into the first two words and the remainder
of the line, and assigns those three fields to $F1, $F2 and $Etc.
The conditional is true if any variables were assigned, i.e. if the pattern
matched.
.Ip "mkdir(FILENAME,MODE)" 8 3
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).