Emulating 'find's print0...

Emulating 'find's print0...

[Meino.Cramer]

Hi,

cat-ting a list of file like so

    cat files.txt | xargs md5sum | sort | .........

fails, if a files name contains blanks.

The tool find circumvent this by using print0
and xargs understands this via -0.

But I dont want to use find in this case, since the 
list of files (files.txt) are hand made and a manual
selection of files.

Is there any way to emulate "-print0" efficiently
(that is: without accessing the drive again) ?

Thank you very much in advance for any help!
Cheers
Meino

Re: Emulating 'find's print0...

[Andreas Perstinger]

On 2016-11-23 08:24, Meino.Cramer@gmx.de wrote:
> cat-ting a list of file like so
>
>     cat files.txt | xargs md5sum | sort | .........
>
> fails, if a files name contains blanks.
>
> The tool find circumvent this by using print0
> and xargs understands this via -0.
>
> But I dont want to use find in this case, since the
> list of files (files.txt) are hand made and a manual
> selection of files.
>
> Is there any way to emulate "-print0" efficiently
> (that is: without accessing the drive again) ?

You could use the -I option of xargs:

$ cat files.txt
test 1
test2
test with more blanks
$ cat files.txt | xargs -I @ md5sum @ | sort
26ab0db90d72e28ad0ba1e22ee510510  test2
6d7fce9fee471194aa8b5b6e47267f03  test with more blanks
b026324c6904b2a9cb4b88d6d61c81d1  test 1

With "-I replstr", xargs always takes a full line and replaces every 
occurence of "replstr" in the argument list of the utility with that line.

The GNU version of xargs also has the -a option which eliminates the cating:

$ xargs -a files.txt -I @ md5sum @ | sort
26ab0db90d72e28ad0ba1e22ee510510  test2
6d7fce9fee471194aa8b5b6e47267f03  test with more blanks
b026324c6904b2a9cb4b88d6d61c81d1  test 1

Bye, Andreas

Re: Emulating 'find's print0...

[Mikael Magnusson]

On Wed, Nov 23, 2016 at 8:24 AM,  <Meino.Cramer@gmx.de> wrote:
> Hi,
>
> cat-ting a list of file like so
>
>     cat files.txt | xargs md5sum | sort | .........
>
> fails, if a files name contains blanks.
>
> The tool find circumvent this by using print0
> and xargs understands this via -0.
>
> But I dont want to use find in this case, since the
> list of files (files.txt) are hand made and a manual
> selection of files.
>
> Is there any way to emulate "-print0" efficiently
> (that is: without accessing the drive again) ?

If you use a reasonable version of xargs, you can specify -d\\n to
only split on newlines. (POSIX xargs doesn't have it, but then again,
POSIX xargs is almost impossible to use safely).

Some examples:
% print -l "one line" "another line" | xargs printf %s\\n
one
line
another
line

% print -l "one'line" "another line" | xargs printf %s\\n
xargs: unmatched single quote; by default quotes are special to xargs
unless you use the -0 option

% print -l "one'line" "another line" | xargs -d\\n printf %s\\n
one'line
another line


-- 
Mikael Magnusson

Re: Emulating 'find's print0...

[Bart Schaefer]

On Wed, Nov 23, 2016 at 8:39 AM, Mikael Magnusson <mikachu@gmail.com> wrote:
> On Wed, Nov 23, 2016 at 8:24 AM,  <Meino.Cramer@gmx.de> wrote:
>> Hi,
>>
>> cat-ting a list of file like so
>>
>>     cat files.txt | xargs md5sum | sort | .........
>>
>> fails, if a files name contains blanks.

I'm surprised no one has yet mentioned zargs.

autoload -Uz zargs

zargs -- "${(@f)$(<files.txt)}" -- md5sum | ...