while

Simple shell loop that repeats while the return value remains zero. More information: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_09_04_09.

• Read stdin and perform an action on every line:

while read line; do echo "$line"; done

• Execute a command forever once every second:

while :; do command; sleep 1; done

• Execute a command until it fails:

while command; do :; done