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 [         


        

Answer 1

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

Answer 2

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.

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Using a while loop:

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

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Using a for loop:

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

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Another way using until:

until [ ]; do foo; sleep 2; done

Answer 3

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

Answer 4

For simple process watching use watch instead

Answer 5

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.

Answer 6

You can use semicolons to separate statements:

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