Re: [perl #108278] -T STDIN hangs

A couple of points have been missed in this discussion.  Firstly, the
willingness to read content from a non-regular file is not specific to
performing the check on an open filehandle.  Perl is perfectly willing
to read content from a non-regular file specified by name:

$ perl -lwe 'print -T "/dev/null" || 0; print -T "/dev/zero" || 0'

Secondly, there's been a bit of the mistaken idea that a non-regular
file is somehow "not a file".  Looking at the documentation of the
file test operators, it's clearly been written using Unix terminology,
in which anything in the filesystem is a file:

#                  -f  File is a plain file.
#                  -d  File is a directory.
#                  -b  File is a block special file.

Given that understanding of what "file" means in this document, we can
better interpret the documentation for -T and -B:

#                  -T  File is an ASCII or UTF-8 text file (heuristic guess).
#                  -B  File is a "binary" file (opposite of -T).
#              The "-T" and "-B" switches work as follows.  The first block or
#              so of the file is examined to see if it is valid UTF-8 that
#              includes non-ASCII characters.  If, so it's a "-T" file.

It speaks of examining the content of "the file".  Doesn't say anything
about it being a regular file.  Just like the documentation for -w et
al doesn't say anything about the file being regular.  -w, -f, and -T
are mutually orthogonal.

Clearly, reading from non-regular files is intentional behaviour,
implemented consistently, and documented.  The choice of such a predicate
for this short spelling may be a questionable language design decision,
but it's too late to change that.  There isn't any viable case for
changing the existing behaviour.  If you want a regular-text-file
predicate, by all means write your own and stick it on CPAN.

This ticket should be closed.

11/14/2017 9:41:37 PM
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