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by ggm 8 days ago

  find -print0 | xargs -0 -I {} "the {} iterated command"
3 comments

Xargs is fine, but openbsd has a -J option and every time I read the man page to figure out how to use it I read the -I and -J options and my brain glazes over.

https://man.openbsd.org/xargs

Other brain glazing obsd wierdness is it's two argument cd command, a cryptid I am unable to wrap my head around.

https://man.openbsd.org/ksh#cd~2

The two arg cd is pretty useful (and, zsh implements it too because cd is a shell feature): if you have parallel directory structure (e.g. the way rails does tests) you can switch from app/b/c/d to spec/b/c/f by doing `cd app spec`
I highly recommend memorizing the POSIX version of every *NIX command and sticking to them. 60% of the time, they work every time. (https://pubs.opengroup.org/onlinepubs/9799919799/idx/utiliti...)
I highly recommend using whatever capabilities are convenient of any utility you're running, and not caring about what other systems do unless you're actually trying to write a portable shell script.
In a world with nix and where nearly every system has zsh, restricting yourself to the POSIX version of these tools is masochistic.
BSD vs linux with a standards committee inbetween.
And for most of those commands add a dash dash so that nothing with a dash prefix turns into options.
why would you ever pipe find into xargs instead of calling -exec?

    find -exec the '{}' iterated command ';'
Because xargs is faster. Exec will invoke the command once per matching file (which is sometimes what you want, of course)!

While xargs will accumulate a bunch of file names, then when it as n names will invoke the command with those names, while continuing to accumulate names until n is reached or the pipe closes.

The size of n depends on the system, but is usually at least a thousand.

the example as given does not accumulate, so that is what i worked with.

    find -exec command '{}' '+' 
accumulates file arguments too. the only advantage of xargs is that you can tell it how many arguments to accumulate,̶ ̶t̶h̶e̶ ̶d̶o̶w̶n̶s̶i̶d̶e̶ ̶o̶f̶ ̶x̶a̶r̶g̶s̶ ̶i̶s̶ ̶t̶h̶a̶t̶ ̶y̶o̶u̶ ̶h̶a̶v̶e̶ ̶t̶o̶ ̶s̶p̶e̶c̶i̶f̶y̶ ̶t̶h̶e̶ ̶n̶u̶m̶b̶e̶r̶,̶ ̶w̶h̶e̶r̶e̶a̶s̶ ̶f̶i̶n̶d̶ ̶j̶u̶s̶t̶ ̶f̶i̶t̶s̶ ̶a̶s̶ ̶m̶a̶n̶y̶ ̶a̶s̶ ̶i̶t̶ ̶c̶a̶n̶.̶
The problem with find is that you can't specify the maximum tolerated command line lengths, and find hasn't historically been very smart about it (it just had a compiled-in value). Apparently this is fixed in GNU find, but for older systems and other platforms that may still be an issue.

Another feature missing in find that xargs has is the maximum processes to start at a time. find will run the commands in sequence, but in many situations you really want to run a bunch in parallel.

good points that i wasn't aware of, thank you. though personally i rarely start huge operations that need to be parallelized so i prefer simplicity over speed.
xargs will fit as many as it can in 128 KiB or the system limit, which is smaller, so in practice, it's almost always pretty similar default packing
you are right, i forgot to check the default. fixed my comment.
The prior has a point because 98.89% of the time I type xargs -n 1 -0 and we are deep in the useless pipe argument which Rob Pike amongst others has rehearsed well.

I do it because I do it, just like why I use egrep and sed in pipes along with awk.

Leah Neukirchen's lr and xe are very nice as a find and xargs replacement (although lr's test flag is way too complex). lr *.file | xe -s ' ... ' is a really great pattern for iterative scripting and hard to get wrong.