On Sat, 6 Jul 2019 at 01:31, Eric Blake <ebl...@redhat.com> wrote: > > On 7/5/19 11:16 PM, Geyslan G. Bem wrote: > >>From 99ed9353c43fc8682f99a70d8a0b97d75f78f3f8 Mon Sep 17 00:00:00 2001 > > From: "Geyslan G. Bem" <geys...@gmail.com> > > Date: Sat, 6 Jul 2019 01:04:40 -0300 > > Subject: [PATCH] cat: open any file name after "--" > > > > * src/cat.c (main): Treat "-" after "--" as file, not as stdin. > > Sorry, but this patch violates POSIX.
I see. 12.2 Utility Syntax Guidelines, Guideline 10 says: "The first -- argument that is not an option-argument should be accepted as a delimiter indicating the end of options. Any following arguments should be treated as operands, even if they begin with the '-' character." And Guideline 13 stands out with "For utilities that use operands to represent files to be opened for either reading or writing, the '-' operand should be used to mean only standard input (or standard output when it is clear from context that an output file is being specified) or a file named -." I think Guideline 13 makes clear that '-' is either stdin or a file named '-' (xor). Thus, my patch embarrassingly violates POSIX. Thank you for point it out. :) > > https://pubs.opengroup.org/onlinepubs/9699919799/toc.htm > > "If a file is '-', the cat utility shall read from the standard input at > that point in the sequence." > > Note that [file...] per the SYNOPSIS is NOT an option, but an argument. > The '--' argument is an end-of-option marker, required only when you > want the next command line word (or all subsequent command line words > when you are not using POSIXLY_CORRECT to suppress GNU getopt argument > permutation) to be recognized as an argument rather than an option. But > since there is no such thing as an empty-string option, '-' is not > recognized as an option in the first place, regardless of whether or not > '--' was present. POSIX sometimes pinches our heels; see, for instance, sh man RATIONALE: "Thus, this volume of POSIX.1‐2008 allows the single <hyphen> to mark the end of the options, in addition to the use of the regular "--" argument, because it was considered that the older practice was so pervasive." When it comes to that piece of software POSIX agrees with a non-standard utility syntax considering '-' as the same as "--". But that's crystal due historical usage. > > If you wish to cat a file named '-' in the current directory, spell it > './-' or use an absolute path to that file. That's true of all command > line utilities that treat '-' as stdin (not just cat). > > -- > Eric Blake, Principal Software Engineer > Red Hat, Inc. +1-919-301-3226 > Virtualization: qemu.org | libvirt.org > -- Regards, Geyslan G. Bem