Date: Fri, 16 Oct 2020 15:19:42 +0200 From: Polytropon <freebsd@edvax.de> To: Ralf Mardorf <ralf-mardorf@riseup.net> Cc: freebsd-questions@freebsd.org Subject: Re: sh scripting question Message-ID: <20201016151942.e01600b6.freebsd@edvax.de> In-Reply-To: <20201016063211.2f8b3a74@archlinux> References: <24456.60388.135834.43951@jerusalem.litteratus.org> <20201015204226099763897@bob.proulx.com> <c6096f5d-84f5-af81-7407-9bda06c7b240@panix.com> <20201016063211.2f8b3a74@archlinux>
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On Fri, 16 Oct 2020 06:32:11 +0200, Ralf Mardorf wrote: > On Thu, 15 Oct 2020 23:14:13 -0400, Kurt Hackenberg wrote: > >On 2020-10-15 23:05, Bob Proulx wrote: > > > >> Oh you are tormenting us now. :-) There are some subtle issues > >> here. > > > > > >Maybe a shell is the wrong tool. > > Exactly! Scripts are useful to handle tasks, such as dealing with > reasonable file names. There is a significant problem with this statement (even though I can understand its intention): At what point does a filename become "not reasonable"? Stupid people do stupid things. Stupidly programmed programs do stupid things to filenames, too. Scripts usually do not care. They typically (!) are not limited to a subset of valid filenames, they work on _all_ filenames. Just imagine you want to copy or delete a file, but the program in question complains that you cannot do it with _this_ file because its name is not reasonable... that would be a really strange situation... > A script should work around reasonable tricky > file names, but at some point bothering with really freakish file names > isn't worth the effort. Depends. If your scope involves processing 1000+ files delivered by your stupid coworkers, you will surely develop a script that fights all the freakish things you will encounter by iterating over those filenames. As I mentioned in my first reply, this is absolutely possible, but not _trivial_ anymore. In my opinion, the goal defines the amount of work you will put into it. > Actually file names should be compatible with > shell, if they are intended to be used with shell scripts. There is a problem. Filenames are subject to restrictions. The first level of restrictions is imposed by the filesystem. It defines a maximum length as well as reserved characters, such as "/" for the directory separator, and "." and ".." which are handled in a specific way. The second level of restrictions comes from the shell. It includes, but is not limited to, using " " (space) as the command and options separator, "-" as the options prefix, and may contain many more, such as "*" or "?". While all of them are valid within a filename, they probably _should_ not be in a filename. If a file should have a name valid on other filesystems which are not as generous as UFS, a third level of restrictions will apply, originating from the limitations of the foreign filesystem, and can even include "forbidden filenames" such as "COM1:". :-) > To some > extent we could use shell scripts, to write little programs, that > probably better should be written in a programming language. At some > extent a programming language is required, a shell script can't do the > job at all or at best it could do the job, but not with reasonable > effort. Fully correct, but also suffers from the lack of a definition of "reasonable" that works everywhere every time. :-) -- Polytropon Magdeburg, Germany Happy FreeBSD user since 4.0 Andra moi ennepe, Mousa, ...
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