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.IX Title "Fatal 3perl"
.TH Fatal 3perl 2024-02-11 "perl v5.38.2" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.if n .ad l
.nh
.SH NAME
Fatal \- Replace functions with equivalents which succeed or die
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\&    use Fatal qw(open close);
\&
\&    open(my $fh, "<", $filename);  # No need to check errors!
\&
\&    use File::Copy qw(move);
\&    use Fatal qw(move);
\&
\&    move($file1, $file2); # No need to check errors!
\&
\&    sub juggle { . . . }
\&    Fatal\->import(\*(Aqjuggle\*(Aq);
.Ve
.SH "BEST PRACTICE"
.IX Header "BEST PRACTICE"
\&\fBFatal has been obsoleted by the new autodie pragma.\fR Please use
autodie in preference to \f(CW\*(C`Fatal\*(C'\fR.  autodie supports lexical scoping,
throws real exception objects, and provides much nicer error messages.
.PP
The use of \f(CW\*(C`:void\*(C'\fR with Fatal is discouraged.
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\f(CW\*(C`Fatal\*(C'\fR provides a way to conveniently replace
functions which normally return a false value when they fail with
equivalents which raise exceptions if they are not successful.  This
lets you use these functions without having to test their return
values explicitly on each call.  Exceptions can be caught using
\&\f(CW\*(C`eval{}\*(C'\fR.  See perlfunc and perlvar for details.
.PP
The do-or-die equivalents are set up simply by calling Fatal's
\&\f(CW\*(C`import\*(C'\fR routine, passing it the names of the functions to be
replaced.  You may wrap both user-defined functions and overridable
CORE operators (except \f(CW\*(C`exec\*(C'\fR, \f(CW\*(C`system\*(C'\fR, \f(CW\*(C`print\*(C'\fR, or any other
built-in that cannot be expressed via prototypes) in this way.
.PP
If the symbol \f(CW\*(C`:void\*(C'\fR appears in the import list, then functions
named later in that import list raise an exception only when
these are called in void context\-\-that is, when their return
values are ignored.  For example
.PP
.Vb 1
\&    use Fatal qw/:void open close/;
\&
\&    # properly checked, so no exception raised on error
\&    if (not open(my $fh, \*(Aq<\*(Aq, \*(Aq/bogotic\*(Aq) {
\&        warn "Can\*(Aqt open /bogotic: $!";
\&    }
\&
\&    # not checked, so error raises an exception
\&    close FH;
.Ve
.PP
The use of \f(CW\*(C`:void\*(C'\fR is discouraged, as it can result in exceptions
not being thrown if you \fIaccidentally\fR call a method without
void context.  Use autodie instead if you need to be able to
disable autodying/Fatal behaviour for a small block of code.
.SH DIAGNOSTICS
.IX Header "DIAGNOSTICS"
.ie n .IP "Bad subroutine name for Fatal: %s" 4
.el .IP "Bad subroutine name for Fatal: \f(CW%s\fR" 4
.IX Item "Bad subroutine name for Fatal: %s"
You've called \f(CW\*(C`Fatal\*(C'\fR with an argument that doesn't look like
a subroutine name, nor a switch that this version of Fatal
understands.
.ie n .IP "%s is not a Perl subroutine" 4
.el .IP "\f(CW%s\fR is not a Perl subroutine" 4
.IX Item "%s is not a Perl subroutine"
You've asked \f(CW\*(C`Fatal\*(C'\fR to try and replace a subroutine which does not
exist, or has not yet been defined.
.ie n .IP "%s is neither a builtin, nor a Perl subroutine" 4
.el .IP "\f(CW%s\fR is neither a builtin, nor a Perl subroutine" 4
.IX Item "%s is neither a builtin, nor a Perl subroutine"
You've asked \f(CW\*(C`Fatal\*(C'\fR to replace a subroutine, but it's not a Perl
built-in, and \f(CW\*(C`Fatal\*(C'\fR couldn't find it as a regular subroutine.
It either doesn't exist or has not yet been defined.
.ie n .IP "Cannot make the non-overridable %s fatal" 4
.el .IP "Cannot make the non-overridable \f(CW%s\fR fatal" 4
.IX Item "Cannot make the non-overridable %s fatal"
You've tried to use \f(CW\*(C`Fatal\*(C'\fR on a Perl built-in that can't be
overridden, such as \f(CW\*(C`print\*(C'\fR or \f(CW\*(C`system\*(C'\fR, which means that
\&\f(CW\*(C`Fatal\*(C'\fR can't help you, although some other modules might.
See the "SEE ALSO" section of this documentation.
.ie n .IP "Internal error: %s" 4
.el .IP "Internal error: \f(CW%s\fR" 4
.IX Item "Internal error: %s"
You've found a bug in \f(CW\*(C`Fatal\*(C'\fR.  Please report it using
the \f(CW\*(C`perlbug\*(C'\fR command.
.SH BUGS
.IX Header "BUGS"
\&\f(CW\*(C`Fatal\*(C'\fR clobbers the context in which a function is called and always
makes it a scalar context, except when the \f(CW\*(C`:void\*(C'\fR tag is used.
This problem does not exist in autodie.
.PP
"Used only once" warnings can be generated when \f(CW\*(C`autodie\*(C'\fR or \f(CW\*(C`Fatal\*(C'\fR
is used with package filehandles (eg, \f(CW\*(C`FILE\*(C'\fR).  It's strongly recommended
you use scalar filehandles instead.
.SH AUTHOR
.IX Header "AUTHOR"
Original module by Lionel Cons (CERN).
.PP
Prototype updates by Ilya Zakharevich <ilya@math.ohio\-state.edu>.
.PP
autodie support, bugfixes, extended diagnostics, \f(CW\*(C`system\*(C'\fR
support, and major overhauling by Paul Fenwick <pjf@perltraining.com.au>
.SH LICENSE
.IX Header "LICENSE"
This module is free software, you may distribute it under the
same terms as Perl itself.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
autodie for a nicer way to use lexical Fatal.
.PP
IPC::System::Simple for a similar idea for calls to \f(CWsystem()\fR
and backticks.