8 ms·
GNU Parallel – The command line power tool
- rcthompson 13y agoi use GNU parallel exclusively in place of xargs simply because it has --dry-run.
- _ZeD_ 13y agowouldn't an "echo" just do the same? $ mkdir a $ cd a $ touch b c d e $ find -type f | xargs echo rm rm ./b ./d ./e ./c $ ls b c d e $ find -type f | xargs rm $ ls $
- jasomill 13y agoOne advantage of "parallel --dry-run" over "xargs echo" is that the former quotes its output: $ touch 'Ham Jam Spam' $ touch 'J.R. "Bob" Dobbs' $ find . -type f -print0 | parallel -n1 -0 --dry-run echo echo ./Ham' 'Jam' 'Spam echo ./J.R.\ \"Bob\"\ Dobbs $ find . -type f -print0 | xargs -n1 -0 echo echo echo ./Ham Jam Spam echo ./J.R. "Bob" Dobbs For my own "dry runs", though, I've always preferred passing the command line to #include <stdio.h> int main(int argc, char* argv[]) { char** argp; int i; printf("argc = %d\n", argc); for (i = 0, argp = argv; *argp != 0; ++argp, ++i) { printf("argv[%d] = %s\n", i, *argp); } return 0; } to remove all reasonable doubt.
- lotsofcows 13y agoQuoting is nice. That's better than bash -x debug mode too.
- peterwwillis 13y agoWhy does the parallel example look weird? It put the single quotes in all the wrong places, and completely around Jam. It should have printed echo './Ham Jam Spam' but your output looks different. As an example of how it should look, try this: $ find . -type f -print0 | xargs -n1 -0 perl -e'print "\"$_\" " for (@ARGV)' "./Ham Jam Spam"
- seryoiupfurds 13y agoIt looks like it's only single-quoting the characters that need it, in his example the newlines.
- davvolun 13y agoHaving never used parallel, I still believe parallel was correct. ./Ham' 'Jam' 'Spam would be identical to ./Ham\nJam\nSpam (if \n were the correct translation to the newline in this case) or './Ham Jam Spam' This would be identical to what you wrote, but only punts to quotes when it doesn't have a canonical method of representing the character otherwise. The fact that you don't need to explicitly concatenate two strings in the shell may be what's throwing you off? Interestingly enough, 'Ham\n\nJam\nSpam' becomes ./Ham' '' 'Jam' 'Spam So parallel is just literally outputting all newlines using quotes. I believe this would be identical, if you analyzed it and saw that two newlines are next to each other: ./Ham' 'Spam' 'Jam
- rcthompson 13y agoWhat if your command has a pipe in it? Then putting echo in front won't work, because the command after the pipe is still executed. The dry run option always works, and doesn't require editing the command itself.
- dredmorbius 13y agoNice. I just had to check to see if xargs has a similar feature. It doesn't, though the --no-run-if-empty and --verbose options are both handy. I believe I've used xargs with "echo <commandlist>" to proof output before committing it. You can simply re-run that piped to bash (or your shell of choice) to execute commands if you wish (say, if parallel isn't available). E.g., echo foo bar baz | xargs -n1 -t echo ls | bash ... will execute 'ls foo; ls bar; ls baz', while showing the expanded command.
- rcthompson 13y agoYes, you can use echo, but that won't work if the command is something like "ls DIR | wc -l".
- dredmorbius 13y agoDepending on how you want to do your counts or piping, you could run that after the xargs / parallel execution, which would be much more efficient (fewer processes and execs) anyhow.
- oofabz 13y agoI use GNU Parallel. I like it because its interface is simple - input is piping filenames to it, just like xargs, and output is nicely collated to the screen. I used to use ppss, which does the core task just as well, but the interface is more complex. I mostly use these tools to optimize large numbers of PNGs before deployment, using optipng, pngout, and/or my own lossypng. These programs take a while to run so using all my cores gets the job done a lot quicker.
- shrike 13y agoI use GNU Parallel with s3cmd to move big data sets in and out of S3. I can easily saturate any network connection. I was able to GET ~2TB from S3 onto a Gluster cluster in a little more than an hour by using GNU Parallel to spread the GETs across 8 instances. Incredibly powerful, easy to use tool.
- ealloc 13y agoI use parallel all the time for embarrasingly parallel scientific computations on a cluster. It is very easy to use and elegant, and it's one of the programs I'm most grateful for. Recently the developers fixed a major bug for me, that child jobs on other nodes would not be killed when parallel was killed. This was the only thing stopping me from recommending it to my labmates, now there's no reason not to use it!
- ole_tange 13y agoRemember to show them 'parallel --bibtex'
- ck2 13y agoI love pssh for simplicity but I guess I better look at fancier stuff too.
- adrianN 13y agoWow, I must have reinvented this particular wheel at least five times.
- mineo 13y agoThis is exactly what I feel like every time I see an article/presentation about (maybe even really small) tools that just get the job done but I didn't know about and didn't even think about looking for although I can think of so many cases where they would've been incredibly useful.
- ole_tange 13y agoA lot of the users of GNU Parallel have felt exactly the same way.
- zurn 13y agoAnybody have a link to a version viewable without proprietary plugins? "Flash Player 9 (or above) is needed to view presentations"
- dreen 13y agoThis looks very similar but is actually a year newer than the slides on slideshare: http://www.luga.de/Angebote/Vortraege/GNU_Parallel_LIT_2011/GNU_Parallel_LIT_2011.pdf http://www.luga.de/Angebote/Vortraege/GNU_Parallel_LIT_2011/...
- felixr 13y agoThe documentation of GNU parallel (https://www.gnu.org/software/parallel/man.html https://www.gnu.org/software/parallel/man.html) also contains a lot of nice examples on how to use parallel.
- gnoe 13y agoIs parallel buggy or is it just me? For example if i have a list of ip addresses: $ cat ips.txt | sort | uniq -c | sort -rn 3 127.0.0.1 2 192.168.1.1 1 192.168.1.2 Now i want to reformat the output of uniq -c, i want the count to the last column: $ cat ips.txt | sort | uniq -c | sort -rn | parallel --colsep ' ' echo {2} {1} But gives empty output.. what gives? It only works if I double pipe it thru parallel like this: $ cat ips.txt | sort | uniq -c | sort -rn | \ parallel --trim lr echo | parallel --colsep ' ' echo {2} {1} 127.0.0.1 3 192.168.1.1 2 192.168.1.2 1
- jftuga 13y agoI wrote a similar program for windows. https://github.com/jftuga/Windows/tree/master/mp https://github.com/jftuga/Windows/tree/master/mp The only file you need to download is mp.exe. Source code is mp.au3.
- RachelF 13y agonifty tool!
- guangnan 13y agoLoad test with parallel: cat urls | parallel --jobs 4 --load 6 'curl -s -w "%{time_total}\n" -o /dev/null {}'