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> do>    echo "hello">    sleep 2> donehellohellohello^C$ <arrow up> while true; do    echo "hello";    sleep 2; done

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

Colon is always "true":

while :; do foo; sleep 2; done

You can use semicolons to separate statements:

$ while [ 1 ]; do foo; sleep 2; done

You can also make use ofuntil command:

until ((0)); do foo; sleep 2; done

Note that in contrast towhile,until would execute the commands inside the loop as long as the test condition has an exit status which is not zero.

Using awhile loop:

while read i; do foo; sleep 2; done < /dev/urandom

Using afor loop:

for ((;;)); do foo; sleep 2; done

Another way usinguntil:

until [ ]; do foo; sleep 2; done

Usingwhile:

while true; do echo 'while'; sleep 2s; done

Usingfor Loop:

for ((;;)); do echo 'forloop'; sleep 2; done

UsingRecursion, (a little bit different than above, keyboard interrupt won't stop it)

list(){ echo 'recursion'; sleep 2; list; } && list;

A very simple infinite loop.. :)

while true ; do continue ; done

Fr your question it would be:

while true; do foo ; sleep 2 ; done

For simple process watching usewatch instead

I like to use the semicolons only for the WHILE statement,and the && 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 && sleep 5s && /usr/bin/launch-mechanism && echo Launching in T-5 && sleep 1s && echo T-4 && sleep 1s && echo T-3 && sleep 1s && echo T-2 && sleep 1s && echo T-1 && sleep 1s && echo liftoff ; done

If you want the while loop to stop after some condition, and yourfoo 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 thefoo 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 with1 when the condition is met and exit with0 when it should be run again.

For example, say you have a python scriptbatch_update.py which updates 100 rows in a database and returns0 if there are more to update and1 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;

You don't even need to usedo anddone. For infinite loops I find it more readable to usefor with curly brackets. For example:

for ((;;)) { date ; sleep 1 ; }

This works inbash andzsh. Doesn't work insh.

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

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.

You can also put that loop in the background (e.g. when you need to disconnect from a remote machine)

nohup bash -c "while true; do aws s3 sync xml s3://bucket-name/xml --profile=s3-profile-name; sleep 3600; done &"

inbash 5 (or perhaps even earlier), you can also reverse the role of the: by running everything in the loop criteria but using: in the loop body instead :

while ( gdate +"%c ( %s.%-N )" && sleep 0.71  ) do :; done  # discards side-effects      while { gdate +"%c ( %s.%-N )" && sleep 0.71; } do :; done  # no sub-shell needed

+ gdate '+%c ( %s.%-N )'Sun Apr 30 12:38:25 2023 ( 1682872705.498728 )+ sleep 0.71+ :+ gdate '+%c ( %s.%-N )'Sun Apr 30 12:38:26 2023 ( 1682872706.218152 )+ sleep 0.71...

meanwhilezsh is even more forgiving, and willing to loop even without the:

while; do gdate +'%c ( %s.%-N )' && sleep 0.31 ; doneSun Apr 30 12:46:09 2023 ( 1682873169.469092 )Sun Apr 30 12:46:09 2023 ( 1682873169.789560 )Sun Apr 30 12:46:10 2023 ( 1682873170.105635 )Sun Apr 30 12:46:10 2023 ( 1682873170.424766 )

• bash
• loops
• while-loop