A few months ago, when I started using Scala more seriously, I familiarised myself with sbt after seeing it touted as the recommended build tool here and there. Despite some grievances with this not-so-simple build tool, I did find one of its features rather handy: automatically executing compile or test actions whenever a file changed (quite similar to hakyll’s preview feature).

In fact, I got used to this feature so much that I decided I needed it for other projects, like automatically running LaTeX for me, or updating ikiwiki.

It turns out this was fairly simple to implement with inotify-tools doing all the heavy lifting, with regard to monitoring files for changes and generating appropriate events. All that remained was wrapping it up in a suitable script I called monitor, to only act on files that match a particular regular expression:

TARGET="$1"
PATTERN="$2"
COMMAND=("${@:3}")

[[ $# -lt 3 ]] && {
 echo "usage: $0 <watched-dir> <file-pattern> <command>"
 exit 1 }

EVENTS=(modify delete)

inotifywait -r -m -e ${(j.,.)EVENTS} --format "%w%f" $TARGET \
| egrep --line-buffered "$PATTERN" | while read file; do
  echo "event: $file"
  $COMMAND
done

I could then run the following command to continuously build my ikiwiki:

monitor path/to/wiki '\.mkdn$|\.mdwn$' ikiwiki --setup ~/wiki.setup

or generate my LaTeX reports (given a suitable Makefile):

monitor path/to/tex '\.tex$|\.bib$' make

The script is also available on github as part of a collection of scripts I have found a use for from time to time.