[SOLVED] echo -e "...\r" and printf "...\r" don't work in shell script

cryptkeeper · 2012-01-13 07:51:52

I've googled for a way to check the status of my vpny-connection. I found this one-liner here http://www.rajatswarup.com/blog/2011/05 … on-status/:

 while [ `ps aux |grep vpnc|grep -v grep|awk '{print $2}'` ] ; do printf "Connected\r"; done

It shows "connected" as long as the vpnc connection is established and ends as soon as the connection's over. Just what I was looking for.

The problem is that it is quite long, so I tried making an alias for it in .bashrc or a short bash script. The problem in case of the .bashrc is that it starts a new line every time it outputs "connected", i.e.

$ alias vpnc-status="while [ `ps aux |grep vpnc|grep -v grep|awk '{print $2}'` ] ; do printf "Connected\r"; done"
$ vpnc-status
connected
connected
connected
connected
connected
connected
connected

When I put the line in a short shell script:

#!/bin/bash
# -> I've also tried #!/bin/sh (just a shot in the dar), but that didn't help either
while [ `ps aux |grep vpnc|grep -v grep|awk '{print $2}'` ] ; do printf "Connected\r"; done

I get this error when I execute it:

/home/<user>/Programming/scripts/vpn-check: line 3: [: 10504: unary operator expected

(the directory is where I put my scripts)

How can I turn this one-liner into a easy-to-write command (script or alias)?

Last edited by cryptkeeper (2012-01-13 12:00:17)

karol · 2012-01-13 07:57:35

'pgrep vpnc' can save you some typing.

cryptkeeper · 2012-01-13 08:21:10

karol wrote:

'pgrep vpnc' can save you some typing.

Thanks, that's easier to type. Well, this returns a number when I have a vpnc connection and nothing when there's no connection. I tried to put this into a short shell script, but something strange happens. I don't have a vpnc connection established right now, and when I write `pgrep vpnc` directly on command line, I get no output. But when I put the same command (and nothing else!) into a shell script:

#!/bin/bash
pgrep vpnc

and execute it I get a number as output!

Now why could THAT be? I'm quite confused...

karol · 2012-01-13 08:24:17

How about reading 'man pgrep'?

DESCRIPTION
pgrep looks through the currently running processes and lists the
process IDs which matches the selection criteria to stdout.

I suggest using a function instead of an alias

# Pick some name for the function
foobarbaz () {
# hides the cursor
  tput civis
# I was testing it with htop, check if it works with your app
  while [ "$(pgrep htop)" ]; do
    printf "\rConnected"
# I set it to check every second
    sleep 1
# Comment out the next two lines if you don't like the blinking
    printf "\r         "
    sleep 1
  done
  printf "\rDiconnected\n"
# shows the cursor
  tput cnorm
}

One problem is that if you exit this function via ^C, it won't show your cursor, you have to run 'tput cnorm' by hand.

Edit: It seems if you put this function in your .bashrc you can't exit it with ^C ;P you have to kill the app you're monitoring (e.g. htop).

Last edited by karol (2012-01-13 08:33:02)

cryptkeeper · 2012-01-13 08:39:27

karol wrote:

How about reading 'man pgrep'?
DESCRIPTION
pgrep looks through the currently running processes and lists the
process IDs which matches the selection criteria to stdout.

Yeah I should have done that... Wouldn't have anything though, I still don't see why it doesn't work as it should if put into a shell script.

I suggest using a function instead of an alias
# Pick some name for the function
foobarbaz () {
# hides the cursor
  tput civis
# I was testing it with htop, check if it works with your app
  while [ "$(pgrep htop)" ]; do
    printf "\rConnected"
# I set it to check every second
    sleep 1
# Comment out the next two lines if you don't like the blinking
    printf "\r         "
    sleep 1
  done
  printf "\rDiconnected\n"
# shows the cursor
  tput cnorm
} 
One problem is that if you exit this function via ^C, it won't show your cursor, you have to run 'tput cnorm' by hand.
Edit: It seems if you put this function in your .bashrc you can't exit it with ^C ;P you have to kill the app you're monitoring (e.g. htop).

Thanks a lot! I simplified it a bit and put this in my .bashrc:

vpnc-check () {
  while [ "$(pgrep vpnc)" ]; do
    printf "\rConnected "
    sleep 1
  done
  printf "\rDiconnected\n"
}

It works like a charm, and I can also abort it with ^C.

But I first tried to put the code in the function body (from while to printf) into a shell script. I have no problems with printf, that works, but again, pgrep vpnc returns a process id even if there's no vpnc connection and a direct pgrep vpnc returns nothing (as it should). Why doesn't this work in a shell script?

karol · 2012-01-13 08:42:43

Try running 'prep -x vpnc' - maybe there's some other process with vpnc in the name.

cryptkeeper · 2012-01-13 11:59:50

Strange, I've tried it again within a shell script, both with and without the -x flag, but now both works...

Whatever. The problem is solved anyway with the function in the .bashrc.

Thanks a lot for your help!

Arch Linux

#1 2012-01-13 07:51:52

[SOLVED] echo -e "...\r" and printf "...\r" don't work in shell script

#2 2012-01-13 07:57:35

Re: [SOLVED] echo -e "...\r" and printf "...\r" don't work in shell script

#3 2012-01-13 08:21:10

Re: [SOLVED] echo -e "...\r" and printf "...\r" don't work in shell script

#4 2012-01-13 08:24:17

Re: [SOLVED] echo -e "...\r" and printf "...\r" don't work in shell script

#5 2012-01-13 08:39:27

Re: [SOLVED] echo -e "...\r" and printf "...\r" don't work in shell script

#6 2012-01-13 08:42:43

Re: [SOLVED] echo -e "...\r" and printf "...\r" don't work in shell script

#7 2012-01-13 11:59:50

Re: [SOLVED] echo -e "...\r" and printf "...\r" don't work in shell script

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