Bash console progress dialog with command output

for i in 10 20 30; do echo $i; sleep 1; done | dialog --title "My Gauge" --gauge "Hi, this is a gauge widget" 20 70

works fine, so @Shadur is right and there is buffering at play.

Adding the sed stripper into the mix shows it is the culprit (only shows 0 and 30):

for i in 10 20 30; do echo $i; sleep 1; done | sed 's/\([0-9]*\).*/\1/' | dialog --title "My Gauge" --gauge "Hi, this is a gauge widget" 20 70

Now that the problem is known, you have multiple options. The cleanest would be to round/cut the percentage in awk with either math or string manipulation, but since you have GNU sed, just adding -u or --unbuffered should do the trick.

However for completeness' sake, a simple test case shows awk also does buffering:

for i in 10 20 30; do echo $i; sleep 1; done | awk '{print $0}' | sed -u 's/\([0-9]*\).*/\1/' | dialog --title "My Gauge" --gauge "Hi, this is a gauge widget" 20 70 

But you already handle that with fflush, so I don't expect problems.

Try adding something like the following to your ~/.xinitrc (or ~/.xsession if you use a login manager):

while true; do
    if [[ -a ~/.messages ]]; then
        zenity --info --text="$(printf "%q" $(cat ~/.messages))"
        rm ~/.messages
    fi
    sleep 10
done &

I haven't tested this with zenity as I don't have it and I'm assuming that .xsession works as expected - I've never used a login manager.

The while/done block will execute indefinitely with a ten second delay between checks (the sleep 10 part). Each time there's a check, the if guard succeeds if there's a non-empty file called .messages in the user's homedir. On success, the contents of the file are read into zenity and the file is removed.

I'm not thrilled with the printf vomit, but it should be fine.

The content that gets put into ~/.messages should be redirected from cron and you'll need to make sure you change the owner and group of the file appropriately. Perhaps something like:

10 * * * * /usr/bin/mything && echo "mything completed" > /home/username/.messages && chown username:groupname /home/username/.messages