Is there a better way to run a command N times in bash

Question

I occasionally run a bash command line like this   n 0  while     n -lt 10     do some command  n    n 1    done   To run some command a number of times in a row -- 10 times in this case   Often some command is really a chain of commands or a pipeline   Is there a more concise way to do this

User · Answer

A little bit naive but this is what I usually remember off the top of my head:

for i in 1 2 3; do
  some commands
done

Very similar to @joe-koberg's answer. His is better especially if you need many repetitions, just harder for me to remember other syntax because in last years I'm not using bash a lot. I mean not for scripting at least.

User · Answer

xargs is fast      usr bin bash echo  while loop   n 0  time while    n    lt  10000     do  usr bin true   done  echo -e   nfor loop   time for   n 0 n lt 10000 n      do  usr bin true   done  echo -e   nseq xargs   time seq 10000   xargs -I   -P1 -n1  usr bin true  echo -e   nyes xargs   time yes x   head -n10000    xargs -I   -P1 -n1  usr bin true  echo -e   nparallel   time parallel --will-cite -j1 -N0  usr bin true      1  10000    On a modern 64-bit Linux  gives   while loop   real    0m2 282s user    0m0 177s sys     0m0 413s  for loop   real    0m2 559s user    0m0 393s sys     0m0 500s  seq xargs   real    0m1 728s user    0m0 013s sys     0m0 217s  yes xargs   real    0m1 723s user    0m0 013s sys     0m0 223s  parallel   real    0m26 271s user    0m4 943s sys     0m3 533s   This makes sense  as the xargs command is a single native process that spawns the  usr bin true command multiple time  instead of the for and while loops that are all interpreted in Bash  Of course this only works for a single command  if you need to do multiple commands in each iteration the loop  it will be just as fast  or maybe faster  than passing sh -c  command1  command2       to xargs  The -P1 could also be changed to  say  -P8 to spawn 8 processes in parallel to get another big boost in speed   I don t know why GNU parallel is so slow  I would have thought it would be comparable to xargs

User · Answer

If you are OK doing it periodically  you could run the following command to run it every 1 sec indefinitely  You can put other custom checks in place to run it n number of times   watch -n 1 some command  If you wish to have visual confirmation of changes  append --differences prior to the ls command   According to the OSX man page  there s also     The --cumulative option makes highlighting  sticky   presenting a   running display of  all  positions  that  have  ever changed   The -t   or --no-title option turns off the header showing the interval    command  and current time at the top of the display  as well as the   following blank line    Linux Unix man page can be found here

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The script file   bash-3 2  cat test sh     bin bash  echo  The argument is  arg   1   for   n 0 n lt  1 n      do   echo  Hi  done   and the output below  bash-3 2     test sh 3 The argument is  arg  3 Hi Hi Hi bash-3 2

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How about the alternate form of for mentioned in  bashref Looping Constructs

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If you re using the zsh shell   repeat 10   echo  Hello      Where 10 is the number of times the command will be repeated

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You can use this command to repeat your command 10 times or more for i in  1  10   do   your command    done  for example for i in  1  10   do   speedtest    done

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I solved with this loop  where repeat is an integer that represents the loops s number  repeat 10 for n in   seq  repeat        do         command1         command2     done

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For one  you can wrap it up in a function   function manytimes       n 0     times  1     shift     while     n -lt  times     do                    n    n 1       done     Call it like     manytimes 3 echo  test    tr  e   E  tEst tEst tEst

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Using a constant  for   n 0 n lt 10 n      do     some command   done  Using a variable  can include math expressions   x 10  for   n 0  n  lt   x   2   n      do some command  done

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All of the existing answers appear to require bash  and don t work with a standard BSD UNIX  bin sh  e g   ksh on OpenBSD    The below code should work on any BSD     echo  1  4   1  4    seq 4 sh  seq  not found   for i in   jot 4   do echo e i  done e1 e2 e3 e4

User · Answer

for run in  1  10   do   command done  Or as a one-liner for those that want to copy and paste easily  for run in  1  10   do command  done  If your ranage has variable use this syntax ref count 10 for i in   seq  count   do     command done

User · Answer

Another simple way to hack it   seq 20   xargs -Iz echo  Hi there    run echo 20 times     Notice that seq 20   xargs -Iz echo  Hi there z  would output      Hi there 1   Hi there 2

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A simple function in the bash config file     bashrc often  could work well   function runx       for   n 0 n lt  1 n         do     2    done     Call it like this     runx 3 echo  Hello world  Hello world Hello world Hello world

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Another form of your example   n 0  while    n    lt  10     do some command  done

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Yet another answer  Use parameter expansion on empty parameters      calls curl 4 times  curl -s -w   n  -X GET  http        www google com    Tested on Centos 7 and MacOS

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xargs and seq will help  function   run times   seq 1  1    shift  xargs -i --             the view    abon abon      run times 3  echo hello world hello world hello world hello world

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for   in  1  10   do command  done      Note the underscore instead of using a variable

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Using GNU Parallel you can do   parallel some command      1  1000    If you do not want the number as argument and only run a single job at a time   parallel -j1 -N0 some command      1  1000    Watch the intro video for a quick introduction  https   www youtube com playlist list PL284C9FF2488BC6D1  Walk through the tutorial  http   www gnu org software parallel parallel tutorial html   You command line with love you for it

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For loops are probably the right way to do it  but here is a fun alternative   echo -e  1  10   n   xargs -n1 some command  If you need the iteration number as a parameter for your invocation  use   echo -e  1  10   n   xargs -I  echo now I am running iteration    Edit  It was rightly commented that the solution given above would work smoothly only with simple command runs  no pipes  etc    you can always use a sh -c to do more complicated stuff  but not worth it    Another method I use typically is the following function   rep     s  1 shift e  1 shift  for x in  seq  s  e   do c         x  sh -c   c   done    now you can call it as   rep 3 10 echo iteration    The first two numbers give the range  The   will get translated to the iteration number  Now you can use this with pipes too   rep 1 10  ls R   wc -l   with give you the number of files in directories R1    R10

[bash] Is there a better way to run a command N times in bash?

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