x xor These operators are documented in perlop.

write FILEHANDLE write EXPR write Writes a formatted record (possibly multi-line) to the specified FILEHANDLE, using the format associated with that file. By default the format for a file is the one having the same name as the filehandle, but the format for the current output channel (see the select function) may be set explicitly by assigning the name of the format to the $~ variable. Top of form processing is handled automatically: if there is insufficient room on the current page for the for

while These flow-control keywords are documented in Compound Statements in perlsyn.

when These flow-control keywords related to the experimental switch feature are documented in Switch Statements in perlsyn.

NAME SYNOPSIS DESCRIPTION NAME warnings::register - warnings import function SYNOPSIS use warnings::register; DESCRIPTION Creates a warnings category with the same name as the current package. See warnings for more information on this module's usage.

SYNOPSIS DESCRIPTIONDefault Warnings and Optional Warnings What's wrong with *-w* and $^W Controlling Warnings from the Command Line Backward Compatibility Category Hierarchy Fatal Warnings Reporting Warnings from a Module FUNCTIONS SYNOPSIS use warnings; no warnings; use warnings "all"; no warnings "all"; use warnings::register; if (warnings::enabled()) { warnings::warn("some warning"); } if (warnings::enabled("void")) { warnings::warn("void", "some warning"); } if (warnings

warn LIST Prints the value of LIST to STDERR. If the last element of LIST does not end in a newline, it appends the same file/line number text as die does. If the output is empty and $@ already contains a value (typically from a previous eval) that value is used after appending "\t...caught" to $@ . This is useful for staying almost, but not entirely similar to die. If $@ is empty then the string "Warning: Something's wrong" is used. No message is printed if there is a $SIG{__WARN__} handler in

wantarray Returns true if the context of the currently executing subroutine or eval is looking for a list value. Returns false if the context is looking for a scalar. Returns the undefined value if the context is looking for no value (void context). return unless defined wantarray; # don't bother doing more my @a = complex_calculation(); return wantarray ? @a : "@a"; wantarray()'s result is unspecified in the top level of a file, in a BEGIN , UNITCHECK , CHECK , INIT or END block, or in a DEST

waitpid PID,FLAGS Waits for a particular child process to terminate and returns the pid of the deceased process, or -1 if there is no such child process. On some systems, a value of 0 indicates that there are processes still running. The status is returned in $? and ${^CHILD_ERROR_NATIVE} . If you say use POSIX ":sys_wait_h"; #... do { $kid = waitpid(-1, WNOHANG); } while $kid > 0; then you can do a non-blocking wait for all pending zombie processes. Non-blocking wait is available on ma

wait Behaves like wait(2) on your system: it waits for a child process to terminate and returns the pid of the deceased process, or -1 if there are no child processes. The status is returned in $? and ${^CHILD_ERROR_NATIVE} . Note that a return value of -1 could mean that child processes are being automatically reaped, as described in perlipc. If you use wait in your handler for $SIG{CHLD}, it may accidentally wait for the child created by qx() or system(). See perlipc for details. Portability