Date: Tue, 22 Sep 2020 19:30:19 +0200 From: Polytropon <freebsd@edvax.de> To: Kurt Hackenberg <kh@panix.com> Cc: freebsd-questions@freebsd.org Subject: Re: Error message output Message-ID: <20200922193019.9ddd63f7.freebsd@edvax.de> In-Reply-To: <25dc8a18-e276-6f6b-685b-377bdf0ffa73@panix.com> References: <20200920191108.22864e5c.freebsd@edvax.de> <528b2c90-18c4-9e95-a150-67344154c66c@holgerdanske.com> <20200921132139.286b5bda.freebsd@edvax.de> <8b426d6f-6ebe-d1a7-13af-69cffbcb6222@holgerdanske.com> <20200922005552.4df3c123.freebsd@edvax.de> <0dc8a3a4-85d9-7168-f118-b456aafd3910@holgerdanske.com> <25dc8a18-e276-6f6b-685b-377bdf0ffa73@panix.com>
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On Tue, 22 Sep 2020 12:53:19 -0400, Kurt Hackenberg wrote: > On 2020-09-22 02:33, David Christensen wrote: >=20 > > Providing a fractional base file name as an argument and computing inpu= t=20 > > and output file names is unconventional.=A0 The FreeBSD convention seem= s=20 > > to be to use complete file names for arguments.=A0 This allows the user= to=20 > > use shell globbing, find(1) and xargs(1), etc., or to wrap this script= =20 > > in another script that computes the arguments. > ... > > When given no options or arguments, the FreeBSD convention seems to be= =20 > > to run the program with a default argument.=A0 If no default makes sens= e,=20 > > then to print the usage message. >=20 >=20 > All true, except these are conventions for all Unixes, not just FreeBSD,= =20 > from sometime early in Unix history. An early example is the program=20 > "cat" (which is easy to write in C). Arguments are input filenames; with= =20 > no arguments it reads stdin. >=20 > The convention that the user supplies file base names, and the program=20 > adds extensions, is strong in some other OSes, including those from=20 > Microsoft and Digital Equipment Corporation. This is tied to the idea,=20 > more or less built into those systems, that the file extension is=20 > separate and special, and has meaning. In fact, in those filesystems,=20 > the file extension is stored separately from the base name, and the '.'=20 > is not stored at all. (Well, I don't know that about NTFS.) >=20 > In Unix, the opposite convention is equally strong: a filename is just a= =20 > single string, and is not parsed; the user supplies complete filenames.=20 > In a Unix filename, '.' is stored as part of the name, and has no=20 > special meaning. A filename can include zero or more suffixes that start= =20 > with '.'. Executable programs usually have zero; "foo.tar.gz" has two. >=20 > Yes, there are mild exceptions -- compilers, make, ls (by default=20 > ignores names that start with '.') -- but this is the origin. Exactly. That's why I should add further development time to the little script; not just that it makes assumptions about file names which _may_ be true, but don't always apply ("base_nnn.png" needs to be resolved where nnn, the counter, is replaced by * and then evaluated by the scripting shell). More flexibility is always better, be it different base names, names not following the format expected, or input file lists generated by a different tool or step. In UNIX, a file can have generally any name, the extension(s) have a meaning usually only to the user; "blah" could be a PDF file, and "xpdf blah" would work, and a C compiler would happily compile a source file named "perry_the_platypus". The interpretation of special cases, such as leading "." by ls, is program-specific. The filesystem adds special interpretation for entries "." and "..", as well as for the character "/", but anything else, non-printable characters, tabs and spaces, special characters, even linebreaks could probably make a truly valid (!) filename. Not all valid filenames are useful, though... ;-) In systems where all parts interpret filenames as a concept of "base.extension", and decide for actions according to extension, the flexibility of UNIX filenames can cause confusion. If you accidentally remove the ".pdf" from a PDF filename, the file can no longer easily be opened (except maybe by "Open with...") until the ".pdf" is added back again; adding ".mp3" instead causes much more confusion for the system and the user. Imagine what stops working if you add a VMS-like ";version". :-) --=20 Polytropon Magdeburg, Germany Happy FreeBSD user since 4.0 Andra moi ennepe, Mousa, ...
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