[bug #61009] xargs need option to immediately stop on command fail

[Bernhard Voelker]

Update of bug #61009 (project findutils):

             Assigned to:                    None => berny                  

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Follow-up Comment #1:

I have to confess that I like the idea of having an option to immediately stop
processing
when an invocation of the command exits with a non-Zero status.

POSIX [1] specifies the following conditions when xargs shall terminate
processing:
* child exits with 255,
* child was killed by a signal, or
* when reading the 'eofstr' string if the '-E eofstr' option is given, or
* when regularly reaching EOF when reading from stdin.
Still, our xargs might implement such an option as a GNU extension.
I would recommend a long-option like --stop-on-error for such an extension.
Why did you propose '-F'?  Is there any precedence in other xargs
implementations?

[1] https://pubs.opengroup.org/onlinepubs/9699919799/utilities/xargs.html

Regarding the examples - and just to be sure:
I assume that the reproducer with 'cp' was just a simplification to
demonstrate
your actual use case, right?  This is my guess because the shown use of
find/xargs
is quite excessive (one cp(1) invocation per file) and unsafe (unusual
filenames
would break the construct).
In such a case - when launching one process per file is required -, I'd maybe
better use the `find -exec ... '{}' \;' syntax without xargs, which could also
be
used in conjunction with -quit to terminate the processing when 'cp' fails:


# Create source and destination directory.
$ mkdir src dst

# Create a regular file 'dst/f' which will cause 'cp' to fail later.
$ touch dst/f

# Create test sub-directories 'a' .. 'g', and a file 'x' in each of them.
$ cd src
$ mkdir a b c d e f g
$ touch a/x b/x c/x d/x e/x f/x g/x

# Run find to copy all files to 'dst', but stopping if 'cp' hits an error.
# Note the use of the '(' ... ')' to enforce the wanted OR-precedence for
-quit
# when cp(1) fails.
$ find . -type f '(' -exec cp -fv '{}' '../dst/{}' \; -o -quit ')'
'./b/x' -> '../dst/./b/x'
cp: cannot create regular file '../dst/./b/x': No such file or directory

# Alternatively, avoid the OR-syntax with -not before -exec:
$ find . -type f -not -exec cp -fv '{}' '../dst/{}' \; -quit


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