OS X Bash watch command

Question

I m looking for the best way to duplicate the Linux  watch  command on Mac  OS  X  I d like to run a command every few seconds to pattern match on the contents of an output file using  tail  and  sed   What s my best option on a Mac  and can it be done without downloading software

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If watch doesn t want to install via   brew install watch   There is another similar copy version that installed and worked perfectly for me  brew install visionmedia-watch   https   github com tj watch

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Use the Nix package manager  Install Nix  and then do nix-env -iA nixpkgs watch and it should be available for use after the completing the install instructions  including sourcing    quot  HOME  nix-profile etc profile d nix sh quot  in your shell

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To prevent flickering when your main command takes perceivable time to complete  you can capture the output and only clear screen when it s done  function watch  while    do a        clear  echo  quot   date  n n a quot   sleep 1   done   Then use it by  watch istats

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I had a similar problem  When I googled  I came across the blog post Install Watch Command on Mac OS X recently  This is not exactly  installing software   but simply getting the binary for the  watch  command

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The shells above will do the trick  and you could even convert them to an alias  you may need to wrap in a function to handle parameters   alias myWatch        while    do clear   2  sleep  1  done        Examples  myWatch 1 ls    Self-explanatory myWatch 5  quot ls -lF  HOME quot     Every 5 seconds  list out home directory  double-quotes around command to keep its arguments together  Alternately  Homebrew can install the watch from http   procps sourceforge net   brew install watch

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Or  in your    bashrc file  function watch       while    do clear  date  echo      sleep 2  done

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Use MacPorts    sudo port install watch

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With Homebrew installed   brew install watch

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You can emulate the basic functionality with the shell loop   while    do clear  your command  sleep 2  done   That will loop forever  clear the screen  run your command  and wait two seconds - the basic watch your command implementation   You can take this a step further and create a watch sh script that can accept your command and sleep duration as parameters      bin bash   usage  watch sh  lt your command gt   lt sleep duration gt   while       do    clear   date    1   sleep  2 done

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Here s a slightly changed version of this answer that    checks for valid args shows a date and duration title at the top moves the  duration  argument to be the 1st argument  so complex commands can be easily passed as the remaining arguments    To use it    Save this to   bin watch execute chmod 700   bin watch in a terminal to make it executable  try it by running watch 1 echo  hi there      bin watch     bin bash  function show help       echo      echo  usage  watch  sleep duration in seconds   command     echo      echo  e g  To cat a file every second  run the following    echo      echo       watch 1 cat  tmp it txt     exit     function show help if required       if     1      help      then       show help   fi   if   -z   1        then       show help   fi    function require numeric value       REG EX    0-9       if       1     REG EX      then     show help   fi    show help if required  1 require numeric value  1  DURATION  1 shift  while    do    clear   echo  Updating every  DURATION seconds  Last updated   date     bash -c        sleep  DURATION done

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It may be that  watch  is not what you want   You probably want to ask for help in solving your problem  not in implementing your solution       If your real goal is to trigger actions based on what s seen from the tail command  then you can do that as part of the tail itself   Instead of running  periodically   which is what watch does  you can run your code on demand      bin sh  tail -F  var log somelogfile   while read line  do   if echo   line    grep -q   Ss ome regex   then       do your stuff   fi done   Note that tail -F will continue to follow a log file even if it gets rotated by newsyslog or logrotate   You want to use this instead of the lower-case tail -f   Check man tail for details   That said  if you really do want to run a command periodically  the other answers provided can be turned into a short shell script      bin sh if   -z   2     then   echo  Usage   0 SECONDS COMMAND   gt  amp 2   exit 1 fi  SECONDS  1 shift 1 while sleep  SECONDS  do   clear      done

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Try this      bin bash   usage  watch  -n integer  COMMAND  case    in     0          echo  Usage  0  -n int  COMMAND                                  sleep 2             esac      if     1      -n     then     sleep  2     shift  shift fi   while         do      clear       echo    date  every   sleep s      echo               sleep  sleep   done

User · Answer

I am going with the answer from here  bash -c  while   0    do  lt your command gt   sleep 5  done   But you re really better off installing watch as this isn t very clean

[macos] OS X Bash, 'watch' command

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