Bash: replace the former output with the new one

[kiyop]

hakerdefo asked a question by private message to me as follows:

I need your help

Sent: 2015-08-05 22:02
by hakerdefo
Hi there kiyop,
I need your help regarding a bash script. I'm working on a script and in that script I need to parse 'StreamTitle' from shoutcast-icecast radio streams. I'm using mpg123 to play the streams. Now with the help of grep and sed I've been able to extract the 'StreamTitle' but here comes my problem. As the track changes in the radio stream the last played track remains on the screen and currently playing track appears below it. Like this,

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The Rolling Stones - Jumpin Jack Flash
Bruce Springsteen - Cover Me

In the above example 'The Rolling Stones - Jumpin Jack Flash' was the track last played and 'Bruce Springsteen - Cover Me' is the currently playing track. As we continue to play the radio stream the list will keep growing. Now I want only the currently playing track displayed in terminal. I don't want the previously played tracks to appear. Is it possible via pure bash solution? Any ideas?
Here is the bash one liner I'm currently using,

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mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep "StreamTitle" | sed -e 's/;.*//' -e 's/.*=//' -e "s/'//g"

Thanks in advance!
Cheers!!!

I answered as follows

Re: I need your help

Sent: 2015-08-07 18:44
by kiyop
If you want to display only the last line of standard output (stdout), add

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|tail -n1

such as

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mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep "StreamTitle" | sed -e 's/;.*//' -e 's/.*=//' -e "s/'//g"|tail -n1

Refer

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man tail

If you want to display only the 2nd line of the standard output, use sed

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|sed -n 2p

Refer

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man sed

Then, hakerdefo replied as follows:

Re: I need your help

Sent: 2015-08-08 00:41
From: hakerdefo
To: kiyop
Thanks for the idea but I already tried it! It didn't work. Adding 'tail -n1' prevents anything from appearing on stdout. Only when you stops mpg123, title of the song that was playing appears on the screen.
Did you try it? I tried it across three different distros and different terminal emulators and the result remains the same.

Thus, I replied as follows:

Re: I need your help

Sent: 2015-08-08 13:26
by kiyop
I have never used mpg123 nor http://streaming.radionomy.com/-1ClassicRock.
So I do not know how the output of the following

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mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null

comes.
It outputs the info of a song whenever it starts playing a new song, doesn't it?
I cannot understand what you want to do.
Where do you execute the command? On a terminal window on GUI? Or on a tty?
Do you want to delete the info of the former song which has been displayed on a terminal, when a new song is started to be played?
If so, you can use "clear" command to delete all the info on the terminal.
But another person may know better way.
Why not posting this question of yours on one of debian user forums directly, instead of asking to me?

Could you please help hakerdefo?

[kiyop]

How about the following?

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refreshsecond=1
mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep "StreamTitle" | sed -e 's/;.*//' -e 's/.*=//' -e "s/'//g" > temporarylogfile &
pid=$(ps|grep mpg123|tail -n1)
while [ -n "$(ps|grep "$pid")" ];do
a=$(tail -n1 temporarylogfile)
clear
echo $a
echo $a > temporarylogfile
sleep $refreshsecond
done
rm -r temporarylogfile

It will delete temporarylogfile in the current directory.

ADDED at Mon Aug 10 10:53:56 JST 2015;

The above
pid=$(ps|grep mpg123|tail -n1)
should be replaced with
pid=$(ps a|grep mpg123|tail -n1)

ADDED at Mon Aug 10 18:53:36 JST 2015;

The above
while [ -n "$(ps|grep "$pid")" ];do
should be replaced with
while [ -n "$(ps a|grep "$pid")" ];do

ADDED at Mon Aug 10 19:48:41 JST 2015;

The above
pid=$(ps|grep mpg123|tail -n1)
and
while [ -n "$(ps|grep "$pid")" ];do
should be replaced with
pid=$(ps a|grep -v grep|grep mpg123|tail -n1|sed -e "s/^ *//" -e "s/ .*//")
and
while [ -n "$(ps a|grep "^ *$pid")" ];do

[hakerdefo]

Thanks Kiyop for posting this on my behalf. To recap my question,
I'm using mpg123 to play radio streams like this one,
http://streaming.radionomy.com/-1ClassicRock
I'm running mpg123 in terminal emulator to play the stream. By default the output looks like following,

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mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null
High Performance MPEG 1.0/2.0/2.5 Audio Player for Layers 1, 2 and 3
	version 1.14.4; written and copyright by Michael Hipp and others
	free software (LGPL/GPL) without any warranty but with best wishes

Directory: http://streaming.radionomy.com/

Terminal control enabled, press 'h' for listing of keys and functions.

Playing MPEG stream 1 of 2: -1ClassicRock ...
ICY-NAME: #1ClassicRock
ICY-URL: http://-1classicrock.playtheradio.com

MPEG 1.0 layer III, 128 kbit/s, 44100 Hz stereo

ICY-META: StreamTitle='The Beatles - Back in the U.S.S.R.';

Now the thing of interest here is the track info 'ICY-META: StreamTitle='The Beatles - Back in the U.S.S.R.';'. So I used grep & sed to extract this info,

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mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep --line-buffered "StreamTitle" | sed -e 's/;.*//' -e 's/.*=//' -e "s/'//g"

Now the output looks like this,

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mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep --line-buffered "StreamTitle" | sed -e 's/;.*//' -e 's/.*=//' -e "s/'//g"
The Beatles - Back in the U.S.S.R

Now as the stream continues to play and the tracks keep changing the output in terminal emulator will keep growing. For example after three tracks change it will look something like,

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The Beatles - Back in the U.S.S.R
The Rolling Stones - Jumpin Jack Flash
Bruce Springsteen - Cover Me

Where 'Bruce Springsteen - Cover Me' is currently playing track and the other two are tracks previously played. Now I only want the currently playing track to appear in the output. I don't want the tracks previously played displayed in terminal emulator output.
Kiyop suggested following,

Code: Select all

mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep --line-buffered "StreamTitle" | sed -e 's/;.*//' -e 's/.*=//' -e "s/'//g" | tail -n1

But this doesn't work. Adding 'tail -n1' to the command prevents anything from appearing on stdout of terminal emulator.
Any idead are welcome!
Cheers!!!

[kiyop]

To hakerdefo,

Have you read my former post: http://forums.debian.net/viewtopic.php? ... 33#p587976 ?
It worked correctly in the case that
"find / > temporarylogfile &"
is used instead of
"mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep "StreamTitle" | sed -e 's/;.*//' -e 's/.*=//' -e "s/'//g" > temporarylogfile &"

And also, tput is useful.
Refer GarryRicketson's post: http://forums.debian.net/viewtopic.php? ... 91#p588091

For example,

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cols=$(tput cols)
tput sc
refreshsecond=1
mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep "StreamTitle" | cut -d \' -f2 > temporarylogfile &
pid=$(ps a|grep -v grep|grep mpg123|tail -n1|sed -e "s/^ *//" -e "s/ .*//")
while [ -n "$(ps a|grep "^ *$pid")" ];do
a=$(tail -n1 temporarylogfile)
wn=$(echo -n "$a"|wc -m)
tput rc
echo -n "$a"
for ((i=1;$i<$[$cols-$wn];i++));do echo -n " "; done
echo $a > temporarylogfile
sleep $refreshsecond
done
rm -r temporarylogfile

I wonder if you don't understand that you can make the above commands into a shell script and that you can execute the shell script.
For example, make a file (such as test.sh) with

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#!/bin/bash
cols=$(tput cols)
tput sc
refreshsecond=1
mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep "StreamTitle" | cut -d \' -f2 > temporarylogfile &
pid=$(ps a|grep -v grep|grep mpg123|tail -n1|sed -e "s/^ *//" -e "s/ .*//")
while [ -n "$(ps a|grep "^ *$pid")" ];do
a=$(tail -n1 temporarylogfile)
wn=$(echo -n "$a"|wc -m)
tput rc
echo -n "$a"
for ((i=1;$i<$[$cols-$wn];i++));do echo -n " "; done
echo $a > temporarylogfile
sleep $refreshsecond
done
rm -r temporarylogfile

and execute it by

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bash ./test.sh

[BowCatShot]

Once you've captured the information line that you want to display, by whatever means you can, you want to place a "\r" at the front of the text string so that each new line overwrites the old one. Here's one of my examples where I display temperature etc. every so often and only produce one line on the screen:

echo -e -n "\r$timenow Temperature $tempf degrees, Humidity $relativehumidity %, Dew Point $dewpointf degrees"

[kiyop]

To BowCatShot,

Thank you for useful info
Indeed,

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for a in 111 2 3;do echo -e -n "\r$a";done

outputs only "3" and the prompt begins just after the output "3" without any new line.

P.S.

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for a in 111 2 3;do echo -e -n "\r$a";done;echo

outputs "311". It is not good

But ...
How does "\r" work correctly for standard output?

hakerdefo asked how to overwrite the former output by the new output of

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mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep "StreamTitle" | sed -e 's/;.*//' -e 's/.*=//' -e "s/'//g"

I made a script "test2.sh" with the following contents:

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#!/bin/bash
i=1
while :;do
echo "test$i"
i=$[1+$i]
sleep 5
done

to output intermittently successive outputs. You know why I do not replace the above

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echo "test$i"

with

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echo -e -n "\rtest$i"

don't you?
mpeg123 may output intermittently without any "\r" without "echo -e -n"

I executed the following to add "\r" in front of each line (output) from "bash ./test.sh":

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bash ./test2.sh|sed -e 's/^/\r/'

and obtained

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test1
test2
test3

and so on. Of no avail.

I executed the following to use 'echo -e -n "\r"':

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echo -e -n "$(bash ./test2.sh|sed -e 's/^/\r/')"

but no output is displayed.

Maybe I do stupid thing
Please tell me how to use 'echo -e -n "\r"' correctly to overwrite former output with the new output from a command which outputs intermittently.

[BowCatShot]

Please tell me how to use 'echo -e -n "\r"' correctly to overwrite former output with the new output from a command which outputs intermittently.

Without delving into the specifics of whatever command you're referring to, I would do something like

var=$(thecommand)
echo -e -n "\r$var"

[kiyop]

To BowCatShot,

Without delving into the specifics of whatever command you're referring to, I would do something like

var=$(thecommand)
echo -e -n "\r$var"

Thank you for the above reply
But I know that such a thing cannot work properly for successive intermittent output from continuing command (without finishing the command), because inputting the value to the valuable does not finish until the command finishes.
I confirmed that It does not work properly.

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var=$(bash ./test2.sh);echo -e -n "\r$var"

did not output anything.
Furthermore, nothing is displayed after I pressed CTRL+c to quit the execution.

Please read hakerdefo's post:
http://forums.debian.net/viewtopic.php? ... 33#p588028

So I used grep & sed to extract this info,

Code: Select all

mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep --line-buffered "StreamTitle" | sed -e 's/;.*//' -e 's/.*=//' -e "s/'//g"

Now the output looks like this,

Code: Select all

mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep --line-buffered "StreamTitle" | sed -e 's/;.*//' -e 's/.*=//' -e "s/'//g"
The Beatles - Back in the U.S.S.R

Now as the stream continues to play and the tracks keep changing the output in terminal emulator will keep growing. For example after three tracks change it will look something like,

Code: Select all

The Beatles - Back in the U.S.S.R
The Rolling Stones - Jumpin Jack Flash
Bruce Springsteen - Cover Me

Where 'Bruce Springsteen - Cover Me' is currently playing track and the other two are tracks previously played. Now I only want the currently playing track to appear in the output. I don't want the tracks previously played displayed in terminal emulator output.

To hakerdefo,

Read one of my former posts: http://forums.debian.net/viewtopic.php? ... 19#p588213

[BowCatShot]

But I know that such a thing cannot work properly for successive intermittent output from continuing command (without finishing the command), because inputting the value to the valuable does not finish until the command finishes.

Well, then I would approach the problem thusly:

I would put the command in question into another batch file in which the output is redirected to a file.

Now from within this batch file that is to do the displaying, I would first off trigger the command batch file to run in the background.

Then within this batch file I would monitor said file for activity. Then using the tail command I would display the last line of the file with the echo statement that I described.

If your situation is such that you could just tail the file at regular, say 1 second, intervals, then the problem becomes really easy.

[kiyop]

To BowCatShot,

I would put the command in question into another batch file in which the output is redirected to a file.

Now from within this batch file that is to do the displaying, I would first off trigger the command batch file to run in the background.

Then within this batch file I would monitor said file for activity. Then using the tail command I would display the last line of the file with the echo statement that I described.

If your situation is such that you could just tail the file at regular, say 1 second, intervals, then the problem becomes really easy.

Thus, you propose similar thing as what I proposed above concretely http://forums.debian.net/viewtopic.php? ... 63#p587976 and http://forums.debian.net/viewtopic.php? ... 63#p588213

[BowCatShot]

Thus, you propose similar thing as what I proposed above concretely

Yes I do. I wasn't trying to steal your thunder, just reinforce it.

[kiyop]

To BowCatShot,

Thus, you propose similar thing as what I proposed above concretely

Yes I do. I wasn't trying to steal your thunder, just reinforce it.

Thank you
I see. The former script of mine can be shrink a little bit:

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refreshsecond=1
wo=0
mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep "StreamTitle" | cut -d \' -f2 > temporarylogfile &
pid=$!
while [ -n "$(ps a|grep "^ *$pid ")" ];do
a=$(tail -n1 temporarylogfile)
wn=$(echo -n "$a"|wc -m)
echo -e -n "\r$a"
for ((i=1;$i<$[$wo-$wn];i++));do echo -n " "; done
echo $a > temporarylogfile # can be omitted
sleep $refreshsecond
wo=$wn
done
rm -r temporarylogfile

To stop unnecessary output,

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refreshsecond=1
wo=0
ao=""
mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep "StreamTitle" | cut -d \' -f2 > temporarylogfile &
pid=$!
while [ -n "$(ps a|grep "^ *$pid ")" ];do
a=$(tail -n1 temporarylogfile)
wn=$(echo -n "$a"|wc -m)
if [ ! "$a" = "$ao" ];then echo -e -n "\r$a";for ((i=1;$i<$[$wo-$wn];i++));do echo -n " ";done;wo=$wn;ao=$a;fi
echo $a > temporarylogfile # can be omitted
sleep $refreshsecond
done
rm -r temporarylogfile

To all,

I really wait better methods.

[Loomx]

How about using pgrep and inotifywait for the loop? Then it doesn't have to check every second.
You might need to sleep 1 before looping to give mpg123 time to start.

e.g.

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mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep "StreamTitle" | cut -d \' -f2 > temporarylogfile &

sleep 1  # wait for mpg123 to start

while pgrep mpg123 >/dev/null; do
    tail -n1 temporarylogfile
    inotifywait -q -e modify temporarylogfile >/dev/null
done

rm -r temporarylogfile

[kiyop]

How about using pgrep and inotifywait for the loop? Then it doesn't have to check every second.
You might need to sleep 1 before looping to give mpg123 time to start.

e.g.

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mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep "StreamTitle" | cut -d \' -f2 > temporarylogfile &

sleep 1  # wait for mpg123 to start

while pgrep mpg123 >/dev/null; do
    tail -n1 temporarylogfile
    inotifywait -q -e modify temporarylogfile >/dev/null
done

rm -r temporarylogfile

Thank you for telling me inotifywait and pgrep

In one of my jessie, inotify-tools ( https://packages.debian.org/en/jessie/inotify-tools ) has not been installed. Thus I should install it before using inotifywait:

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apt-get install inotify-tools

To replace the former output with the new one, the following may be better although I have not confirmed that the following works correctly:

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wo=0
mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep "StreamTitle" | cut -d \' -f2 > temporarylogfile &
sleep 1
while pgrep mpg123 >/dev/null; do
    a=$(tail -n1 temporarylogfile)
    wn=$(echo -n "$a"|wc -m)
    echo -e -n "\r$a";for ((i=1;$i<$[$wo-$wn];i++));do echo -n " ";done
    wo=$wn
    inotifywait -q -e modify temporarylogfile >/dev/null
done
rm -r temporarylogfile

The above script will not stop if mpg123 had been executed before the above script was executed.

[hakerdefo]

Sorry for a delayed reply
Thanks a metric ton kiyop for your valued suggestions
Thanks also to BowCatShot and Loomx for some great input
I was working on an Internet radio player script and this question was asked specifically for a section of that script. I've already released the first version of the script into the wilderness of www,

pmrp (Poor Man's Radio Player)

I definitely will be taking advantage of the suggestions made in this thread to improve the script in the future.
Thanks again to all of you!
Cheers!!!

[kiyop]

I will check https://github.com/hakerdefo/pmrp

[kiyop]

I read https://github.com/hakerdefo/pmrp/blob/master/pmrp
The above displays all the titles of the played radio stream including the old ones, doesn't it?

You may be able to shrink the script by using arrays. For example,
lines from #138 to #264 may be able to be replaced with the following:

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function UrbaN_181fM (){

Name=("Jammin 181" "Old School HipHop" "The Beat" "The Box" "Trinity" "True R&B")

link=("http://relay.181.fm:8042" "http://relay.181.fm:8068" "http://relay.181.fm:8054" "http://relay.181.fm:8024" "http://icyrelay.181.fm/181-trinityhiphop_128k.mp3" "http://relay.181.fm:8022")

clear

echo -e "Stations Playing $BLUE Urban Music $NC :"
echo ""
for i in 1 2 3 4 5 6
do
echo -e "$BLUE 0$i $NC ${Name[$[i-1]]}"
done
echo -e "$RED 07 $BLUE Return to 181FM Menu $NC"
echo ""
echo -e "Select a $BLUE station $NC between 1 to 6 and hit $BLUE [Enter] $NC to $BLUE PLAY $NC :"

read PLAY
if test "$PLAY" -ge 1 -a "$PLAY" -le 6 2>/dev/null
then
clear
echo -e "$BLUE PMRP $NC -> $BLUE 181FM $NC -> $BLUE Urban $NC -> $BLUE ${Name[$[i-1]]} $NC:"
echo ""
echo -e "Press $BLUE [Space] $NC to pause : Press $BLUE [Q] $NC to stop"
echo ""
echo ""
echo -e "$BLUE Playlist $NC:"
echo ""
$PLAYER "${link[$[i-1]]}" 2>&1 /dev/null | grep --line-buffered "StreamTitle" | sed -e 's/;.*//' -e 's/.*=//' -e "s/'//g"
UrbaN_181fM
elif [ "$PLAY" = 7 ]
then
clear
181fM
fi
clear
echo ""
echo -e "$RED $PLAY $NC $BLUE is an invalid selection! $NC"
echo ""
sleep 3
UrbaN_181fM
} 

You can also use "dialog" for selector.
You can install dialog by executing the following with root privilege:

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apt-get install dialog

And you can read manual of dialog:

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man dialog

[hakerdefo]

I read https://github.com/hakerdefo/pmrp/blob/master/pmrp
The above displays all the titles of the played radio stream including the old ones, doesn't it?

Yes, it does.
And thanks for the great tip. That tip not only shrinks the script but makes it more readable and easier to understand.
Cheers!!!

[HarborView]

This works because xterm takes ANSI positioning codes.
See:
http://www.tldp.org/HOWTO/Bash-Prompt-HOWTO/x361.html

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#!/bin/bash
x="Now is the time*for all good men*to come to the aid*of their country"
IFS="*"
X=($x)
clear
for ((k=0; k<4; k++)); do 
  echo ${X[k]}
  sleep 1
done
echo

MoveUp=`echo -e "\033[1A"`
ClearLine=`echo -e "\033[K"`
echo "Press ENTER for the 2nd part"
read
echo
echo
for ((k=0; k<4; k++)); do 
  echo -n $MoveUp$ClearLine
  echo ${X[k]}
  sleep 1
done

[kiyop]

Thank you for telling ANSI positioning codes
The former script of mine which does not display unnecessary output can be shrink a little bit:

Code: Select all

refreshsecond=1
ao=""
mpg123 http://streaming.radionomy.com/-1ClassicRock 2>&1 /dev/null | grep "StreamTitle" | cut -d \' -f2 > temporarylogfile &
pid=$!
echo -ne "\033[s"
while [ -n "$(ps a|grep "^ *$pid ")" ];do
a=$(tail -n1 temporarylogfile)
if [ ! "$a" = "$ao" ];then echo -ne  "\033[u\033[K$a";ao=$a;fi
echo $a > temporarylogfile # can be omitted
sleep $refreshsecond
done
rm -r temporarylogfile