This and other RFCs are available on the web at http://dev.perl.org/rfc/ =head1 TITLE Shell Style Redirection =head1 VERSION Maintainer: David Nicol <[EMAIL PROTECTED]> Date: 8 Aug 2000 Last Modified: 5 Sep 2000 Mailing List: [EMAIL PROTECTED] Version: 2 Number: 66 Status: Developing =head1 ABSTRACT The C<use redirect> pragma or a new C<redirect> keyword is introduced to allow redirection of streams of any kind into each other. The keyword may not be really needed, as when does it make any sense to do a lt or gt comparison with a file handle? =head1 SUMMARY sub callfritz{ local STDIN < $InputData; local STDOUT > PREVIOUSLY_OPENED_HANDLE; eval `cat fritz.pl`; }; is proposed as an alternative to doing the same thing with a variety of open2 calls. =head1 DESCRIPTION As an alternative to the Bourne shell style C<open> syntax described in `perldoc -f open`, this proposal overloads the less than and greater than operators in order that subsequent statements, particularly external routines that will be looking to a file descriptor table for their file handles, will get from and give to where we want them to. The redirection is affected by the scoping operators like any other variable which alters the situation. It will also provide another way to capture STDERR from within backticks. sub ToolErrorsFirst{ # place to hold the output my $tooloutput; # place to hold the errors my $errors; # use redirect: very similar to shell redirection my use redirect STDOUT > $tooloutput ; # alternately, FILE > $scalar is obviously a redirect # (if we accept the overload of >) # so no additional keywords are required my STDERR > $errors ; $tooloutput = `tool @_`; return $errors . $tooloutput; }; Currently I do this kind of thing by using the file system as temporary storage. another use of the angle brackets would be as a single-character print operator, similar to << in C++ streams. print $abc; print OUT $z; # one way to do it < $abc; OUT < $z; # another way to do it Left-angle could differ from C<print> by returning the file handle, instead of a success code, making C++ like constructions possible: < $this < "and" < $that; # same as print "${this}and$that" =head1 IMPLEMENTATION We need overloading based on type. The < operator will be like C<print> when there is a file handle on the left side, it will be like assigning from <FH> when there is a file handle on the right, and it will be like the Bourne shell duplicate C<open> when there are file handles on both sides. Setting up a way to trap the standard error from a forked process and load it into a scalar -- will that be difficult? =head1 MIGRATION Code that compares file handles, or compares file handles with scalars, will break. =head1 CHANGES discussion of C++ and use of < as a print operator =head1 REFERENCES RFC 39: Perl should have a print operator RFC 61: Interfaces for linking C objects into perlsubs
