[ILUG] Re: script handling filenames with spaces

[Ian Spillane]

Yikes! ;-)

On 8/19/07, Brian Foster <blf at utvinternet.ie> wrote:
>
>   | From: "Ian Spillane" <iantheteacher at gmail.com>
>   | Date: Sun, 19 Aug 2007 11:28:43 +0100
>   |
>   | Piping FIND into WHILE looks elegant. Like that solution
>   | myself; but for the sake of argument I did once rely on
>   | this inelegant solution with temporarily replacing spaces
>   | in filenames (to "{}") before looping:
>   |
>   |     for file in $(find -name whatever | sed s/[\ ]/{}/g)
>   |     do
>   |         f=$(echo $file | sed s/{}/\ /g ) # return spaces
>   |         cat "$f"
>   |     done
>   |
>   | If you have to use FOR then it's a solution - but wouldn't
>   | recommend. WHILE is nicely reliable for filenames.
>
> yea, I pipe stuff all the time into "while" loops
> (including, at least once, the output of another
> "while" loop!).  it's a powerful trick, and if yer
> careful, only(?) fouls up on newlines-in-filenames.
>
> anyways, with respect to the above sed(1) example,
> I see three worries off the top of my head (and I'm
> ignoring the newline issue):
>
> 1st, a filename containing "{}" will go wrong.
>      hence, I'd either use something find(1) should
>      never output, such as "//" or "/../", albeit
>      those can go wrong in a weird(?) case (left as
>      an exercise to the reader).  or, I'd somehow
>      "escape" any contained "{}".
>
> 2nd, as written, tabs-in-filenames are not handled,
>      albeit those can clearly be handled by a similar
>      trick.  but then you've probably got two instances
>      of the 1st problem ....  ;-(
>
> 3rd, echo(1) doesn't always print its arguments
>      literally, even after fixing the bug in the
>      above — adding the missing double-quotes:
>
>         f=$(echo "$file" | sed ... )
>
>      exactly what sorts of 'echo' arguments can
>      foul up depends on yer system and settings,
>      but examples include "-n" and "foo\123bar".
>      to avoid those gotchas, and when using GNU
>      bash(1)'s built-in echo(1), I often use "-E":
>
>         f=$(echo -E "$file" | sed ... )
>
>      albeit printf(1) is perhaps the best solution,
>      but on older systems it's not a shell built-in.
>
> another possible bug in the above is if the filename
> happens to be something like "--help" then the cat(1)
> may foul up?  (actually, the shown find(1) tends to
> prefix all names with "./" so this isn't a problem.)
>
> of course, filenames containing newlines, or "{}",
> or which are "--help", and so on, are all rather
> (extremely!) rare — spaces in filenames are much
> more common — and so most of the time can simply
> be ignored, treated as errors, whatever.   but,
> if yer writing a script that should be robust,
> (e.g., when you don't have precise control over,
> or knowledge of, the input) these sort of odd
> cases need to be worried about.
>
> cheers!
>         -blf-
>
> p.s.  incidently, is there any reason for using
>      the RE "[ ]" rather than " "?  that is, why
>      bother with the character class?  (I'm ignoring
>      that "[" and "]" are _also_ unquoted shell
>      metacharacters (which does not, in this case,
>      matter?).)  the use of an RE character class
>      doesn't hurt (AFAIK), but (IM(H?)O) makes the
>      RE a tad harder to read, esp. if yer trying
>      to untangle whether the square-brackets (and
>      curly braces) really are supposed to be shell
>      globbing or not ....
>
> --
> ▶ ▶  I AM CURRENTLY LOOKING FOR A JOB!  ◀ ◀ | Brian Foster
> Experienced (>25 yrs) software engineer:    |        Montpellier, FRANCE
> • Unix, Linux, embedded, design-for-test;  | Stop E$$o (ExxonMobile)!
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Ian Spillane
Cork College of Commerce
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http://www.corkcollegeofcommerce.ie
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