How to use inotifywait to watch a directory for creation of files of a specific extension

how do I modify the inotifywait command to report only when a file of certain type/extension is created

Please note that this is untested code since I don't have access to inotify right now. But something akin to this ought to work:

inotifywait -m /path -e create -e moved_to |
    while read path action file; do
        if [[ "$file" =~ .*xml$ ]]; then # Does the file end with .xml?
            echo "xml file" # If so, do your thing here!
        fi
    done

Use a double negative:

inotifywait -m --exclude "[^j][^s]$" /path -e create -e moved_to |
    while read path action file; do
        echo "The file '$file' appeared in directory '$path' via '$action'"
    done

This will only include javascript files

Whilst the double-negative approach of the previous answer is a nice idea since (as TMG noted) it does indeed shift the job of filtering to inotifywait, it is not correct.

For example, if a file ends in as then it will not match [^j][^s]$ because the final letter s does not match [^s], therefore it will not be excluded.

In Boolean terms, if S is the statement:

"the final letter is s"

and J is the statement:

"the penultimate letter is j"

then the value of the --exclude parameter should semantically equate to not(J and S), which by De Morgan's laws is not(J) or not(S).

Another potential problem is that in zsh, $path is a built-in variable representing the array equivalent of $PATH, so the while read path ... line will completely mess up $PATH and cause everything to become unexecutable from the shell.

Therefore the correct approach is:

inotifywait -m --exclude "[^j].$|[^s]$" /path -e create -e moved_to |
    while read dir action file; do
        echo "The file '$file' appeared in directory '$dir' via '$action'"
    done

Note the . which is needed after [^j] to ensure that the match is applied in the penultimate position, and also that the | character (representing the boolean OR mentioned above) should not be escaped here because --exclude takes POSIX extended regular expressions.

However, please see and upvote @ericcurtin's answer which for newer versions of inotifywait is a far cleaner approach.