Syntax for a single-line Bash infinite while loop

Question

I am having trouble coming up with the right combination of semicolons and or braces  I d like to do this  but as a one-liner from the command line   while   1   do     foo     sleep 2 done

User · Answer

A very simple infinite loop       while true   do continue   done   Fr your question it would be   while true  do foo   sleep 2   done

User · Answer

For simple process watching use watch instead

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It s also possible to use sleep command in while s condition  Making one-liner looking more clean imho   while sleep 2  do echo thinking  done

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If I can give two practical examples  with a bit of  emotion     This writes the name of all files ended with   jpg  in the folder  img    for f in    do if      f          jpg     then echo  f  fi  done   This deletes them   for f in    do if      f          jpg     then rm -r  f  fi  done   Just trying to contribute

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If you want the while loop to stop after some condition  and your foo command returns non-zero when this condition is met then you can get the loop to break like this   while foo  do echo  sleeping      sleep 5  done    For example  if the foo command is deleting things in batches  and it returns 1 when there is nothing left to delete    This works well if you have a custom script that needs to run a command many times until some condition  You write the script to exit with 1 when the condition is met and exit with 0 when it should be run again   For example  say you have a python script batch update py which updates 100 rows in a database and returns 0 if there are more to update and 1 if there are no more  The the following command will allow you to update rows 100 at a time with sleeping for 5 seconds between updates   while batch update py  do echo  sleeping      sleep 5  done

User · Answer

Using while    while true  do echo  while   sleep 2s  done   Using for Loop   for         do echo  forloop   sleep 2  done   Using Recursion   a little bit different than above  keyboard interrupt won t stop it    list    echo  recursion   sleep 2  list     amp  amp  list

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You can try this too  WARNING  this you should not do but since the question is asking for infinite loop with no end   this is how you could do it   while    0 -ne 1     do echo  it s looping     sleep 2  done

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Colon is always  true    while    do foo  sleep 2  done

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I like to use the semicolons only for the WHILE statement  and the  amp  amp  operator to make the loop do more than one thing     So I always do it like this  while true   do echo Launching Spaceship into orbit  amp  amp  sleep 5s  amp  amp   usr bin launch-mechanism  amp  amp  echo Launching in T-5  amp  amp  sleep 1s  amp  amp  echo T-4  amp  amp  sleep 1s  amp  amp  echo T-3  amp  amp  sleep 1s  amp  amp  echo T-2  amp  amp  sleep 1s  amp  amp  echo T-1  amp  amp  sleep 1s  amp  amp  echo liftoff   done

User · Answer

You can also make use of until command   until   0    do foo  sleep 2  done   Note that in contrast to while  until would execute the commands inside the loop as long as the test condition has an exit status which is not zero     Using a while loop   while read i  do foo  sleep 2  done  lt   dev urandom     Using a for loop   for         do foo  sleep 2  done     Another way using until   until      do foo  sleep 2  done

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while true  do foo  sleep 2  done   By the way  if you type it as a multiline  as you are showing  at the command prompt and then call the history with arrow up  you will get it on a single line  correctly punctuated     while true  gt  do  gt     echo  hello   gt     sleep 2  gt  done hello hello hello  C    lt arrow up gt  while true  do    echo  hello      sleep 2  done

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You can use semicolons to separate statements     while   1    do foo  sleep 2  done

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You don t even need to use do and done  For infinite loops I find it more readable to use for with curly brackets  For example  for          date   sleep 1      This works in bash and zsh  Doesn t work in sh

[bash] Syntax for a single-line Bash infinite while loop

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