Re: Suggestions for rm [WAS: Re: Feature request: install package by passing URL to apt-get]

[Joel Roth <joelz@pobox.com>]

On Sat, Jun 25, 2022 at 09:45:58AM -0400, Greg Wooledge wrote:
> On Fri, Jun 24, 2022 at 07:42:25PM -1000, Joel Roth wrote:
> > I list the files first:
> > 
> > ls some-pattern
> > 
> > then add a pipe to rm:
> > 
> > ls some-pattern | rm 
> > 
> > or
> > 
> > ls some-pattern | rm -rf
> 
> Those commands do not work.  rm does not read a list of files from stdin.
> 
> Even if you were to add xargs, those commands still would not work in
> all cases.  They would only work in the simplest cases, where none of
> the filenames contain whitespace, single-quote characters, or double-quote
> characters.
> 
> That's because xargs does not split its input on newlines.  It splits
> its input on "quoted words".  Like this:
> 
> unicorn:~$ echo 'a list of "quoted words"' | xargs printf '<%s>\n'
> <a>
> <list>
> <of>
> <quoted words>
> 
> Any unbalanced single or double quote will cause an error:
> 
> unicorn:~$ echo "I don't know.mp3" | xargs printf '<%s>\n'
> xargs: unmatched single quote; by default quotes are special to xargs unless you use the -0 option
> <I>
> 
> And even if xargs *did* have some option to split its input only on
> newlines, a filename that *contains* a newline would still break it.
> 
> Finally, ls does not always reproduce filenames exactly.  There are
> some systems (I'm not sure about all versions of Debian, but definitely
> some Unix systems) where certain characters will be printed as
> question marks by ls.  That means any file containing one of those
> characters would make the ls|xargs rm construct fail.
> 
> If you want to use ls as a preview for what will be removed, that's
> perfectly fine.  You just can't use "up arrow | xargs rm" as your
> follow-up command.  Instead, use "up arrow" and then use command editing
> to replace the ls with rm.

I was actually using 'xargs rm' in an alias. Thanks for
pointing out the limitations. 

-- 
Joel Roth