zsh: add watch_file command

uses inotifywait to watch writes on a file and executes a specific
action whenever this is changed (killing the previous process)

functions/misc.zsh

@@ -278,15 +278,43 @@ function mangrep() {
 
 # watches the given file and executes the given action whenever the file is changed. Usage: watch_file <file> <command>
 function watch_file() {
-  if ! which inotifywait &>/dev/null ; then echo "$0 requires inotifywait"; return 1; fi
-  [[ -z "$1" ]] && "Usage: $0 <file> <action>" && return 1
-  local file
-  file="$1"
+  if ! which inotifywait 2>&1 &>/dev/null ; then echo "$0 requires inotifywait"; return 1; fi
+
+  [[ -z "$1" ]] && echo "Usage: $0 <file> <action>" && return 1
+  local file=$1
   shift
 
-  [[ -z "$@" ]] && "Usage: $0 <file> <action>" && return 1
+  [[ -z "$@" ]] && echo "Usage: $0 <file> <action>" && return 1
 
-  local action
-  action="$@"
-  while inotifywait -e close_write "$file"; do zsh -c "$action"; done
+  local action="$@"
+  local _bg_job_pid
+
+  local TRAPINT(){
+
+    if [[ -n ${_bg_job_pid} ]]; then
+        kill -9 ${_bg_job_pid}
+    fi
+    yellow '\nQuitting.'
+    break;
+  }
+
+  {
+      set +m # disable job control messages
+      while true; do
+          zsh -c "$action" &
+          _bg_job_pid=$!
+          disown
+          echo -e "$Cyan ==> Running \"$action\" with pid=${_bg_job_pid}$CLEAR"
+
+          # block until the file has been written to
+          inotifywait -e close_write "$file" &>/dev/null
+
+          # the job might have failed, ignore errors
+          kill -9 ${_bg_job_pid} &>/dev/null || true
+      done
+  } always {
+    # remove ctrl-c trap
+    unset -f TRAPINT
+    set -m # restore job control messages
+  }
 }