/

regexp/

 

 

See m/regexp/.

?regexp?

Like m/regexp/ search, but match only once between calls to the reset operator.

Execute the accept(2) system call. Return the packed address upon success, the undefined value otherwise. See also socket, listen.

Deliver a SIGALRM after seconds-1 seconds, or cancel scheduled delivery if seconds is 0. Return the number of seconds remaining on the previously scheduled timer. See also kill, %SIG.

Execute the bind(2) system call. name must be a packed address of the proper type for the socket. Return non-zero if successful, the undefined value otherwise. See also socket, pack.

Return current subroutine's context as ($package, $filename, $line). With expr, return additional info (used by the debugger).

Change permissions of the given list of files to mode (an integer). Return the number of files successfully changed. See also stat, chown, utime, rename.

Remove the last character from a string (default: $_ ) or from each of a list of strings. Return the last character removed.

Set the owner and group ID's of the given list of files to uid and gid, respectively. Return the number of files changed. See also stat, chmod, utime, rename.

Return a string containing the character in the character set represented by the integer-valued expr. See also ord.

Cause dirName (default $_ ) to become the root directory of the filesystem, as perceived by the current process. A dirName of "/" refers to the system root. See also chdir.

Close the given file or pipe, reset the line counter ($. ), and, if fileHandle refers to a pipe, wait for the process to terminate and place the exit status of the child process into $?. Return non-zero if successful and the undefined value otherwise. See also open, pipe.

Close a directory opened by opendir.

Call connect(2). name must be a packed address of the proper type for the socket. See also socket .

Return the cosine of expr (default $_), expressed in radians.

Remove the binding between a dbm file and the associative array, assocArray. DEPRECATED: use untie .

Bind a dbm or ndbm database, dbName, to the associative array, assocArray. Create it with the protections specified by mode (as modified by the current umask) if the database does not already exist. DEPRECATED: use tie.

Return true iff the lvalue expr is currently defined. See also undef.

Print the string value of list to STDERR, appending " at script line line \n" if list does not end in a newline, and exit with value: ($! ? $! : ($?>>8) ? ($?>>8) : 255). Inside an eval, assign the string to $@ rather than printing it, and return the undefined value from the eval. See also exit, print, warn.

Execute block, returning the value of the last command executed in it. When modified by a loop modifier, execute block once before testing the loop condition. See also eval, while, unless.

Execute the perl commands contained in the file, fileName. If fileName is a relative pathname and cannot be found from the current directory, then search for it from each directory in @INC. See also require.

Cause perl to dump core. If label is given, arrange to execute the command "goto label" if restarted after an undump(l), rather than restarting the script.

Iterate over an associative array. Each time executed, return another element of associative array, assocArray, as a 2-element array consisting of the element's key and value, or the null array if all elements have been returned. Subsequent execution will restart the iteration. See also keys , values, foreach.

Call endgrent(3). See also setgrent, getgrent.

Call endhostent(3). See also sethostent, gethostent.

Call endnetent(3). See also setnetent, getnetent.

Call endprotoent(3). See also setprotoent, getprotoent.

Call endpwent(3). See also setpwent, getpwent.

Call endservent(3). See also setservent, getservent.

For the first form, return 1 if fileHandle is at end-of-file, or unopened, otherwise return 0. If no arguments are specified, default to the last file read. If the null list is given, default to the last file in the command-line series (<>). See also open, close.

Parse and execute the perl code given by expr (default $_ ), or within the block, in the current program context. Upon success, set $@ to the null string and return the value of the last expression evaluated. Fatal errors or execution of the die command cause the undefined value to be returned and $@ to be set to the error message. See also do.

Execute the execve(2) system call, transforming the current process into a new one. The full pathname of the command to be executed may be given by progVar, a scalar variable (the first element of argv is used by default), and the elements of the list, argv, form its command line. If given a single argument containing Bourne shell metacharacters, then execute the command "/bin/sh -c argv" instead. This command does not return if successful. See also fork, system.

Exit immediately with the integer value of expr (0 by default). See also die.

Return e^x (x defaults to $_). See also die.

Execute the fcntl(2) system call, if available. This command requires the fcntl.ph perl library module. The scalar argument may be used and/or set, depending on function. Return the undefined value if the ioctl (2) system call returns -1, the string "0 but true" if it returns 0, and the return value itself otherwise. See also ioctl, flock , syscall.

Return the file descriptor for fileHandle. See also $!, open.

Execute the flock(2) system call, if available. See also fcntl, syscall.

Execute the fork(2) system call. Return the child PID in the parent process and 0 in the child process. Return the undefined value if unsuccessful. See also exec, pipe, shell.

Return the next character from the file referenced by fileHandle (STDIN by default), or the null string upon end-of-file. See also read.

Return the current login name, as given in /etc/utmp . If none found, return the null string. See also getpwuid, getpwent, @ENV.

Return the packed sockaddr address of the other end of the connection, socket. See also getsockname , socket, accept, bind, unpack.

Return the current process group of the process identified by pid (or the current process if pid is 0 or unspecified). See also setpgrp, getppid, $$.

Returns the process id of the parent process. See also $$.

Call getpriority(2) to return the current priority of a process, process group, or user. See also setpriority, $$, $<, getpgrp.

Call the C library routine of the same name. If an appropriate group entry is found, return the list ($name, $passwd, $gid, $members) in an array context or the group name (GID for getgrnam) in a scalar context. $members is a space-separated list of the login names belonging to the group. Otherwise, return the null list or the undefined value, depending on context. See also setgrent, endgrent.

Call the C library routine of the same name. If an appropriate host entry is found, return the list ($name, $aliases, $addrtype, $length, @addrs) in an array context or the host name (address for gethostbyname) in a scalar context. where the @addrs value is the list of addresses in raw form. In the Internet domain, unpack them with "($a,$b,$c,$d) = unpack('C4',$addr[0]); " Upon failure, return the null list or the undefined value, depending on context, and return the value of the h_errno variable in $? , if supported. See also sethostent , endhostent.

Call the C library routine of the same name. If an appropriate network entry is found, return the list ($name, $aliases, $addrtype, $net) in an array context or the network name (network address for getnetbyname ) in a scalar context. Otherwise, return the null list or the undefined value, depending on context. See also setnetent , endnetent, gethostbyaddr, upack.

getprotobynumber(number)
getprotoent

Call the C library routine of the same name. If an appropriate protocol entry is found, return the list ($name, $aliases, $proto) in an array context or the protocol name (protocol number for getprotobyname ) in a scalar context. Otherwise, return the null list or the undefined value, depending on context. See also setprotoent , endprotoent.

Call the C library routine of the same name. If an appropriate login entry is found, return the list ($name,$passwd,$uid,$gid,$quota,$comment,$gcos,$dir,$shell) in an array context or the login name (UID for getpwnam) in a scalar context. Otherwise, return the null list or the undefined value, depending on context. See also setpwent, endpwent, getlogin.

Call the C library routine of the same name. If an appropriate service entry is found, return the list ($name,$aliases,$port,$proto) in an array context or the service name (service port for getservbyname ) in a scalar context. Otherwise, return the null list or the undefined value, depending on context. See also setservent , endservent.

Return the packed sockaddr address of the local end of the connection, socket. See also getpeername , socket, unpack.

Return the socket option requested or undefined if an error occurs. See also setsockopt, socket.

Convert the time as returned by time (or expr, if given) to an array of the form: ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) . $mon has the range [0..11] and $wday has the range [0..6] (Sunday = 0). The values are computed with respect to Greenwich Mean Time. See also localtime .

Resume execution at the statement labeled label. The labelled statement cannot be nested inside a do () construct. See also if, unless, while, until, for, "Goto Statement Considered Harmful," by Edsker Djkstra, CACM.

For each element of list, evaluate expr in a context in which $_ references the element, and return either an array consisting of those elements for which the expression evaluated to true, or the number of times the expression was true, depending on context. See also map, foreach.

Return the decimal value of expr (default $_ ) interpreted as a number in hexadecimal notation. See also int, oct.

Return x+$[, where x is the number of characters in str preceeding the first occurrence, if any, of substr, beginning at or after its (position - $[ - 1)'th character, and $[ - 1 otherwise. The default value of position is 0. See also m/regexp/ .

Return the value of expr ($_ by default) interpreted as a decimal integer. See also hex.

Execute the ioctl(2) system call. This command requires the ioctl.ph perl library module. The scalar argument may be used and/or set, depending on function. Return the undefined value if the ioctl (2) system call returns -1, the string "0 but true" if it returns 0, and the return value itself otherwise. See also fcntl, pack, unpack, require.

Return the string formed by the concatenation of the elements of listOrArray, separated by the string expr. See also split.

Return an array containing all the keys of the associative array, assocArray, or the number of keys, depending on context. See also values, each.

Send signal sig (either an integer or a quoted signal name) to each of the processes (or process groups, if sig has a "-" prefix) whose ID's are given in list. Return the number of processes successfully signalled. See also %SIG.

immediately terminate the innermost enclosing loop, or the loop labelled by label, if specified. Any continue block associated with the loop is not executed. See also next, while, until, for, foreach.

Return the number of characters in expr ($_ by default).

Create a new name, newFile, for the file referred to by oldFile. Return 1 upon success, 0 otherwise. See also symlink, unlink, rename.

Execute the listen(2) system call. See also socket.

Create new instantiations of the lvalues in list, to be used by the innermost enclosing block, subroutine, eval, or do command, and all subroutines called within it, and return the list. The instantiations are destroyed upon exit from it. See also my.

Convert the time as returned by time (or expr, if given) to an array of the form: ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) . $mon has the range [0..11] and $wday has the range [0..6] (Sunday = 0). The values are computed with respect to the local timezone. See also gmtime.

Return log_e(x). The value x defaults to $_. See also exp.

Equivalent to the stat command unless file (a filehandle or a file name) references a symbolic link. In that case, provide values for the symbolic link itself, rather than for the object to which it refers. See also readlink.

In a scalar context, return 1 and set $1, $2, etc., and $`, $', $&, and $+ (see the descriptions for these variables) iff the variable-interpolated regexp matches the target string, otherwise return the undefined value. In an array context, return the array of substrings matched by subexpressions in regexp (or (1), if none) iff the variable-interpolated regexp matches the target string (no variables are set), otherwise the null array.

The default regexp is the last successfully marched regexp. The target string is $_ unless otherwise specified using the =~ or !~ operator. The initial "m" allows any non-alphanumeric character to be the pattern delimiter instead of "/". The "i" option causes case-insensitive matching; the "o" option forces variable-interpolation to be performed only once; and the "g" option, in a scalar context, causes iteration through the string on each successful evaluation, or, in an array context, it causes the array returned to contain all substrings matched by the subexpressions in regexp for all possible matches in the target string (or all matches if no subexpressions). See also s/regexp/replacement/, grep.

Create directory dirname with permissions "mode & umask". If successful return 1, otherwise return 0 and set $!. See also rmdir, opendir.

Execute the msgctl(2) system call, Return the undefined value if the system call returns -1, the string "0 but true" if it returns 0, and the return value itself otherwise. See also msgget, msgsnd, msgrcv, pack, unpack.

Execute the msgget(2) system call. Return the message queue ID, or the undefined value on error. See also msgctl, msgsnd, msgrcv, pack, unpack.

Execute the msgsnd(2) system call to send message msg to message queue id. msg must begin with a packed, long integer message type. See also msgctl, msgget, msgrcv, pack, unpack.

Execute the msgrcv(2) system call to receive a message from message queue id into scalar variable var of maximum size size. If a message is received, the packed, long integer message type is the first thing in var, and the maximum length of var is size plus the size of the message type. See also msgctl, msgget, msgsnd, pack, unpack.

Execute the continue block, if any, associated with the innermost enclosing loop, or the loop labelled by label, if specified, and begin a new iteration of the loop. See also last, continue.

Return the decimal value of expr (default $_ ) interpreted as a number in octal notation, or in hexadecimal notation if it begins with "0x". See also hex, int.

Open a file whose name is given by expr, or a pipe to a new process whose command line is given by expr, and associate it with fileHandle. expr defaults to $fileHandle. Return non-zero upon success (the PID of the subprocess, in the case of a pipe), or the undefined value otherwise.

If expr begins with one of "< ", ">", ">> ", or "+>", then open the file given by the remainder of expr with read-only, write-only, append, or read/write access, respectively ("<" by default). An "& " appearing immediately after each of these indicates the remainder of expr is a file descriptor (if numeric) or a file handle. In that case, dup it and associate fileHandle with the duped file descriptor.

For a pipe, expr either starts with a "| " or ends with one, to produce a pipe to the subprocess or a pipe frrom it, respectively. See also read, write, close, pipe.

Open a directory named expr. Returns non-zero if successful, or the undefined value if not. See also readdir, telldir, seekdir, rewinddir, closedir.

Return the numeric ASCII value of the first character of expr (default: $_). See also chr, int.

Pack an array or list into a binary structure. Return a string containing the structure. template is a string consisting of packing code letters and optional repeat or length specifiers. See also unpack.

Open a pair of buffered, connected pipes like the corresponding system call. See also open, $|.

Return the last value of array, after removing it from the array, or the undefined value if array is empty. See also push.

Print the comma-separated list of strings to the file referenced by fileHandle (the default is the currently selected output channel). If list is also omitted, print $_. Return non-zero if successful. See also printf , write.

Equivalent to "print fileHandle sprintf(list)''. See also sprintf, write.

Push the values of list onto the end of the array array, increasing the length of array by the length of list. See also pop.

Return a random fractional number between 0 and the value of expr (expr should be positive, and defaults to 1). See also srand.

Read length bytes from fileHandle. Place the bytes into scalar, beginning at offset (0 by default). Return the number of bytes read, or the undefined value upon error. scalar will be resized to exactly contain the bytes read. See also write, sysread.

Return the next directory entry (all of the rest of the entries, in an array context) from the directory referred to by dirHandle. If there are no more entries, return the undefined value (or the null list). See also opendir.

Return the value of a symbolic link named by expr ($_ by default). On error, return the undefined value (setting $! (ERRNO)). See also lstat, symlink.

Receive a len-byte message on socket filehandle socket, placing the message into scalar, which will be resized to exactly contain the message. Return the address of the sender, or the undefined value if there's an error. Takes the same flags as recv(2). See also socket, send.

Restart the enclosing loop block labelled with label (the default is the innermost enclosing loop) without evaluating the conditional again or the continue block, if any. See also next, last.

Change the name of file oldName to newName, returning 1 if successful, 0 otherwise. This command cannot rename a file in such a way that would require the file to change filesystems. See also link.

Execute the file specified by expr ($_ by default) at this point in the current script, if it hasn't already appeared in a previous require statement (using this name). The last statement evaluated in the file must return non-zero, or a fatal error is raised. See also use.

Clear all variables in the current package that begin with the letters referred to by expr, or reset ?regexp? search expressions, if expr is omitted. expr is interpreted as a list of single characters and character ranges (indicated with hyphens). Only reset variables or searches in the current package. Always returns 1.

Return list from the current subroutine. See also sub.

In an array context, return an array value consisting of the elements of list in the opposite order. In a scalar context, return a string value consisting of the bytes of the first element of list reversed. See also map.

Set the current position to the beginning of the directory for readdir on dirHandle. See also seekdir, opendir.

Return the position of the last occurrence of substr at or before position in str. See also index, m/regexp/.

Delete the directory dirName (default: $_ ), which must be empty. Return 1 if successful. Return 0 and set $! (ERRNO) otherwise. See also unlink, mkdir.

Replace the string matching regexp (by default the most recent successfully matched regular expression) with replacement in the operand specified by a =~ or !~ operator, or in $_ by default. Return the number of substitutions made. flags can be zero or more of: g, indicating that all occurrences of the pattern are to be replaced; i, indicating that matching is case-insensitive; e, to evaluate replacement as an expression rather than just a double-quoted string; and o, to cause evaluation of replacement to occur only once. Any non-alphanumeric delimiter may replace the slashes. If single quotes are used, no interpretation is done on the replacement string (the e modifier overrides this, however). If backquotes are used, the actual replacement text is the output of the command given by replacement. If regexp is delimited by bracketing quotes, then replacement has its own pair of quotes. See also m/regexp/.

Force expr to be interpreted in a scalar context and return the resulting value. See also int, join, wantarray.

Position the file pointer for fileHandle to the position'th byte from the beginning of the file if whence is 0, from the current file pointer position if whence is 1, and from the end of the file if whence is 2. Return 1 if successful, 0 otherwise. See also tell, open, seekdir.

Set the current position for the readdir routine on dirHandle to pos. pos must be a value returned by telldir. See also opendir, seek.

Set the current default output fileHandle to fileHandle, and return the previously selected fileHandle. See also write, print, $" , $|.

Suspend execution of the current process until I/O or exceptional conditions exist on the file descriptors specified by the file descriptor masks, rmask, wmask, and emask. Wait at most timeout seconds, or forever if timeout is undef. Return the time left to wait (on most implementations, otherwise timeout). See also select(2), vec, fileno, time, sleep.

Call the System V IPC function semctl(2). If cmd is &IPC_STAT or &GETALL, then arg must be a variable which will hold the returned semid_ds structure or semaphore value array. Return the undefined value for error, "0 but true" for zero, or the actual return value otherwise. See also semget,.semop.

Calls the System V IPC function semget(2). Returns the semaphore id, or the undefined value on error. See also semctl, semop.

Calls the System V IPC function semop(2) to perform semaphore operations such as signaling and waiting. optstring must be a packed array of semop structures. Return non-zero if successful, or the undefined value on error. See also semctl, semget.

Send a message an a socket. Takes the same flags as send(2). On unconnected sockets you must specify a destination to send to. Return the number of characters sent, or the undefined value on error. See also recv, socket.

Call the C library routine of the same name. See also getgrent, gethostent, getnetent.

Set the current process group for the specified pid (default: 0, for the current process). Produce a fatal error if used on a machine that doesn't implement setpgrp(2). See also setpgp.

Set the priority for a process, process group, or user. See also getpriority.

Call the C library routine of the same name. See also setprotoent(3), setpwent(3), setservent(3), getprotoent, getpwent, getservent.

Set the socket option requested. Returns undefined if there is an error. optVal may be specified as undef if you don't want to pass an argument.

Removes the first element from array (defaults to @ARGV at top-level, @_ in subroutines) and returns it, shortening the array by 1. Returns the undefined value if the array is empty. See also unshift, push, pop.

Call shmctl(2). If cmd is &IPC_STAT, then arg must be a variable which will hold the returned shmid_ds structure. Return the undefined value upon error, "0 but true " for zero, or the actual return value otherwise. See also shmget.

Call shmget(2). Return the shared memory segment id, or the undefined value upon error. See also shmread , shmwrite , shmutil.

Read size bytes into var, starting from the pos'th byte of shared memory segment id by attaching to it, copying out, and detaching from it. Return true if successful, false upon error. See also shmwrite, shmget.

Write the first size bytes of string into shared memory segment id, starting at the pos'th byte of id by attaching to it, copying in, and detaching from it. If string is too short, nulls are written to fill out size bytes. Return true if successful, false upon error. See also shmread , shmget.

Shut down a socket connection in the manner indicated by how, which has the same interpretation as shutdown(2). See also socket.

Return the sine of expr (default is $_ ), in radians. See also cos.

Sleep for expr seconds (default: until the next signal). Return the number of seconds actually slept. See also time, select.

Open a socket of the specified type and attach it to filehandle socket. domain, type, and protocol are specified the same as for socket (2). Return true if successful, false otherwise. See also accept, bind, connect, getpeername, getsockame, getsockopt, listen, recv, send, setsockopt, shutdown, socketpair.

Create an unnamed pair of sockets in the specified domain, of the specified type. domain, type, and protocol are specified the same as for the system call of the same name. Returns true if successful, false otherwise. See also pipe.

Sort list using subroutine as the comparison function (ascending lexicographic comparison, by default) and return the sorted array value. subroutine may be the name of a non-recursive subroutine that returns a negative integer if the value referenced by the predefined value, $a, is ordered before that referenced by $b, a positive integer if after, and 0 otherwise. subroutine may also be a scalar variable whose value names such a subroutine, or a block. See also <=>, cmp.

Remove the elements designated by offset and length from array, and replace them with the elements of list, if any. Return the elements removed. If length is omitted, remove everything from offset onward. See also split, join.

Split expr ($_ by default) into an array consisting of the first limit (the default is no limit) strings in expr separated by strings matching regExp (default /[ \t\n]+/). In an array context, return the array. In a scalar context, set @_ to the array and return the number of fields found. If the regExp contains parentheses, additional array elements are created from each matching substring in the delimiter. See also join.

Return a string formatted by the usual printf conventions. (The '*' character is not supported).

Return the square root of expr (default is $_).

Set the seed for the random number generator used by rand to expr (default: time).

Return the array ($dev, $ino, $mode, $nlink, $uid, $gid, $rdev, $size, $atime, $mtime, $ctime, $blksize, $blocks) for the file referenced by fileHandle, or named by expr. return the values from the last stat or filetest if fileHandle is an underline. Return the null list upon error. See also lstat, open.

Preprocess scalar ($_ by default), optimizing internal pattern-matching mechanisms for performing pattern matching on it. See also m/regExp/, s/regExp/replacement/.

Return the len-character substring of expr beginning at offset. A negative offset indicates a position relative to the end of the string. If len is omitted, return everything up to the end of the string. If expr is an lvalue, the entire substr may function as an lvalue. See also index , m/regExp/, s/regExp/replacement/.

Create a symbolic link, newFile, with contents oldFile. Return 1 upon success, 0 otherwise. See also link, open, lstat.

Call the system call whose index is the first element of the list, passing it the remaining elements as arguments. See also sysread, syswrite, stat, fork, exec, system.

Read length bytes from fileHandle using read(2). Place the data into scalar, beginning at offset. Return the number of bytes actually read, or undef upon error. See also read, syswrite, syscall, open.

Fork a child process, executing "exec list" in the child. Wait for the child process to complete, returning its exit status as returned by wait(2). See also fork.

Write length bytes from scalar, beginning at offset, to fileHandle, using write(2). Return the number of bytes actually written, or undef upon error. See also print, write, sysread, syscall, open.

Return the current file position for fileHandle (default is the file last read). See also seek , open, telldir.

Return the current directory position for dirHandle. See also seekdir, opendir, tell.

Bind variable to package packageName, which provides the implementation for the variable. Pass list to the "new" method of the package. See also untie.

Return the number of non-leap seconds since 00:00:00 UTC, January 1, 1970. See also gmtime, localtime.

Return a four-element array, ($user,$system,$cuser,$csystem), giving the user and system times, in seconds, for this process and its children. See also fork.

Translate all occurrences of the characters found in the search list with the corresponding character in the replacement list. Return the number of characters replaced or deleted. If no string is specified via the =~ or !~ operator, the $_ string is translated. Modifiers are: c - complement the character set searchList; d - delete characters in searchList not found in replacementList; s - replace sequences of characters translated to the same character to a single instance of the character. If replacementList is shorter than searchList and the d modifier is not present, the replacementList is padded with its final character to increase its length to that of searchList. replacementList may be null, in which case searchList is used as its value. See also substr, m//.

Set the umask for the process to expr (a numeric value) and return its previous value. If expr is omitted, return the current umask. See also chdir, open, mkdir.

Undefine the value of the lvalue, expr, if any, which may be a scalar value, an array, or a subroutine name (prefixed with &). Always return the undefined value. See also delete.

Delete a list of files and return the number of files successfully deleted. See also rmdir.

Expand the string expr into an array value as directed by template. Return the array, or the first value of the array in a scalar context. template has the same format as for pack. In addition, a prefix of "%< number>" (default 16) indicates a <number>-bit checksum of the items instead of the items themselves. Default is a 16-bit checksum. See also vec.

Break the binding between variable and its package. See tie.

Prepend list to the front of array, and return the number of elements in the resulting array. See also shift, push.

Change the access and modification times on each file of a list of files. The first two elements of list must be the numerical access and modification times. Return the number of files successfully changed. See also open.

Return an array containing the values in assocArray, or, in a scalar context, the number of values. See also keys, each.

Wait for a child process to terminate. Return the PID of the deceased process, or -1 if there are no child processes. The child's termination status is returned in $?. See also fork , waitpid.

Wait for a particular child process to terminate. Returns the PID of the deceased process, or -1 if there is no such child process. The child's termination status is returned in $?. Valid values for flags are system-dependent. See also fork, wait.

Return true if the current subroutine is being evaluated in an array context. Return false in a scalar context. See also scalar.

Print the string value of list to STDERR, appending "at script line line \n" if list does not end in a newline. See also die, print.

Write a formatted record to the specified file, 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 select) may be set explicitly by assigning the name of the format to the $~ variable.

Top of form processing is handled automatically: if there is insufficient room on the current page for the formatted record, the page is advanced by writing a form feed, a special top-of-page format 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 selected. The number of lines remaining on the current page is in variable $-, 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 select operator. If the is an expr, then the expression is evaluated and the resulting string is used to look up the name of the fileHandle at run time. See also print.