I have encountered this in the syntax for case after calling help case and getting case WORD in [PATTERN [| PATTERN]...) COMMANDS ;;]... esac.
There was a question, whether "in" is a bash operator, but answers were answering the script problem of the person rather than saying clearly whether there is or it is an operator at all. I tried to find it in Bash documentation, but since in is a natural language preposition, the search provides lots of hits. Trying to find it as an operator, I was not successful.
fooin Bash?" by invokingtype fooin Bash (ortype -a fooif you want). This works for manyfoos, includingin; trytype in. – Kamil Maciorowski Apr 18 '23 at 14:49