Question

I’m trying write simple notify app in bash. I want to read output from mplayer, parse it and display through notify-send.

I can get desired info from mplayer using this:

mplayer <url> | grep ICY

and then parse in using sed.

I create named pipe, tell mplayer to write it and then I’m reading from it. Unfortunately, it doesn’t work. Here’s my script:

$fifo=~/.rp/fifo
mkfifo $fifo

mplayer <url> 2>/dev/null | grep ICY 1> $fifo &

while read line < $fifo; do
    echo $line
done

wait

Program keeps waiting to input from $fifo. I tried following in other terminal, while this script is running:

1. Run

   echo "Test" > .rp/fifo
   

   Terminal with running script shows “Test”

2. Run

   echo "ICY" | grep ICY > .rp/fifo
   

   also works.

3. Run

   mplayer <url> | grep ICY > .rp/fifo
   

   and it doesn’t work.

Is I said above, the combination of mplayer | grep works fine. grep > $fifo works fine. I don’t understand why mplayer | grep > $fifo doesn’t work.

Answer 1

You could do unbuffered grep with:

$ mplayer ...  2>&1 | grep --line-buffered "ICY"

or better:

$ mplayer ...  2>&1 | sed -une 's/^.*ICY[^:]*: //p'

or even, why not (sed is very nice for grep and formatting),
this will grep ICY lines and even split line containing - in a first field of 30 chars length separed by a : from a second field:

$ mplayer ...  2>&1 |
    sed -une "
        /ICY/{
            s/^.*ICY[^:]*:.*'\([^']*\)';/\1/;
            s/^\(.*\) - /\1                              - /;
            s/^\(.\{30\}\) *- /\1: /;
            p;
    }"

could give something like:

Artist name                  : Song title
Other artist                 : Other song
Unsplited line
Artist                       : Title