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Display runnning countdown in a bash script?

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# 1  
Display runnning countdown in a bash script?

I am looking for a way to display on a single line, a running countdown for a given amount of time in a terminal using a bash script.

I am looking for this to use as part of a larger bash script that captures Video. The script sets up a bunch of parameters for DVgrab, and one of the parameters set is the tape length. I would like to use this $tape_length as the input for a running countdown so that at any time during capture I can see how much longer the capture will run for.

On a side note, in my script $tape_length is entered in the form hh:mm:ss

I feel like this should be easy, but despite some extensive searching I can't find any leads or even scripts to steal and modify! Any help is much appreciated, I'm very new to bash scripting...
# 2  
This uses a few tricks to do what you want:
  • The printf command does NOT append a linefeed automatically unless you tell it to.
  • Setting IFS to something else lets the shell split things apart into arrays on whatever delimiter you want, in this case , :.
  • The date command can be used to produce time in seconds.
  • Carriage returns return the cursor to the beginning of the line without moving to the next line.

function countdown
        local OLD_IFS="${IFS}"
        local ARR=( $1 )
        local SECONDS=$((  (ARR[0] * 60 * 60) + (ARR[1] * 60) + ARR[2]  ))
        local START=$(date +%s)
        local END=$((START + SECONDS))
        local CUR=$START

        while [[ $CUR -lt $END ]]
                CUR=$(date +%s)

                printf "\r%02d:%02d:%02d" \
                        $((LEFT/3600)) $(( (LEFT/60)%60)) $((LEFT%60))

                sleep 1
        echo "        "

countdown "00:07:55"

# 3  

That is exactly what I needed Thanks! At first it was counting down and then starting the capture, but I just added an "&" and she works great!


(Just wanted to include this for search purposes...)
# 4  
Originally Posted by Corona688
This uses a few tricks to do what you want:
Great little script, Corona688, just what I needed! Smilie

Here's a little variant I wrote that allows you to prefix the countdown timer with a custom message:

countdown "00:07:55" Time left before entering the matrix

... which produces something like:

Time left before entering the Matrix > 00:00:08

Here's my patch:

pvdb@localhost ~ $ diff original prefix 
<         local ARR=( $1 )
>         local ARR=( $1 ) ; shift
>         IFS="${OLD_IFS}"
>         local PREFIX="$*" ; [ -n "${PREFIX}" ] && PREFIX="${PREFIX} > "
<                 printf "\r%02d:%02d:%02d" \
>                 printf "\r${PREFIX}%02d:%02d:%02d" \
<         IFS="${OLD_IFS}"
pvdb@localhost ~ $ _

# 5  
Great idea, thanks for the patch! But since your copy/paste of it wasn't identical down to the last bit of whitespace and newline(possible disagreement on spaces per tab, etc) I'm having trouble applying it... diff -U is generally preferred these days as it gives more complete information on what's being replaced where, but a full code-listing really can't be that much larger.

But I think I see a potential problem in your use of printf: if your PREFIX variable includes control sequences like %d it will cause printf to do strange things since it will insert parameters from the commandline. Try inserting %s instead of PREFIX, and making "${PREFIX}" the first argument printf is given. This will guarantee the string is printed as 100% literals.
# 6  
Originally Posted by Corona688
countdown "00:07:55"

That will fail for 00:08:09.

Here is my version, which will work in any POSIX shell:

  set -- $*
  secs=$(( ${1#0} * 3600 + ${2#0} * 60 + ${3#0} ))
  while [ $secs -gt 0 ]
    sleep 1 &
    printf "\r%02d:%02d:%02d" $((secs/3600)) $(( (secs/60)%60)) $((secs%60))
    secs=$(( $secs - 1 ))

# 7  
Hi cfajohnson,

Thanks for your version of the script... very enlightening!

Quick question: instead of doing a "raw" sleep...

sleep 1

your version does this instead...

    sleep 1 &

I'm assuming doing it does way minimizes the "skew" on the actual time spent in the function, ie. every cycle is as close to 1 second as possible, as opposed to 1 second + however long it takes to do all the work.

Is that correct, or is there another benefit in doing it this way?



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