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Re: Backslash mysteriously disappears in command expansion when unescapi


From: Robert Elz
Subject: Re: Backslash mysteriously disappears in command expansion when unescaping would reference an existing file
Date: Thu, 23 May 2019 05:10:00 +0700

    Date:        Wed, 22 May 2019 17:34:22 +0000
    From:        Charles-Henri Gros <address@hidden>
    Message-ID:  <address@hidden>

  | The problem I'm trying to solve is to iterate over regex-escaped file
  | names obtained from a "find" command. I don't know how to make this
  | work. It works with other versions of bash and with other shells.

You were relying upon a common bug, which has been fixed in bash, but
your technique is all wrong, you don't need any kind of loop at all, not
a for loop, and not the while read loop that Greg suggested.

find -print produces a list of names, one per line.   Those are simple
strings, which fgrep (or grep -F as Andreas suggested) can handle finding.

What I'd do is

        fgrep "$(find .... -print)" wherever

(You can use grep -F if you have an aversion to using its traditional name,
but fgrep was once a different program to grep / egrep).

This version will have a problem with filenames with embedded newlines,
but so did your original, so I am simply assuming that you have none of
those (using any variant of grep to search for strings containing newlines
tends to be "difficult" as grep is a line at a time tool).

If you version of grep cannot handle the pattern list not having a
terminating \n (the $() removes it) then you can add it back

        fgrep "$(find ... -print)"$'\n' wherever.

You're probably still going to need a | into sed inside the command
substitution, as I doubt that you actually want to look for filenames
in the format that find prints them (you have never shown your actual
command) and I suspect that you want to delete the pathname component
(a leading "./" or whatever) and it isn't clear what you want to
happen with filenames in subdirectories.  But none of those manipulations
will affect anything.

The other difference between this method and the one that you were
using, is that this one will mix up the output for all of the different
file names (it reads the target files just once, looking for all of the
filenames simultaneously) whereas your original scheme looked for each
file name in the target sequentially (re-reading the target file(s) over
and over again for each new file name).   That would group output lines
for each file name together, whereas the technique above does not.

kre




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