Output something (in a loop) until a key is pressed

Question

I'm trying to make a stopwatch, and when user press Q I want to exit.

I found two script, one where a clock is displayed until ctrl + z is pressed. And one script that exit if "q" is pressed.

I've tried to combined them, but "read" seems to mess it all up.

The reason I want to achieve this is that if the user press Q the time elapsed will be saved to a file.

Stopwatch:

BEGIN=$(date +%s)

echo Starting Stopwatch...

while true; do
   NOW=$(date +%s)
   let DIFF=$(($NOW - $BEGIN))
   let MINS=$(($DIFF / 60))
   let SECS=$(($DIFF % 60))
   let HOURS=$(($DIFF / 3600))
   let DAYS=$(($DIFF / 86400))

   # \r  is a "carriage return" - returns cursor to start of line
   printf "\r%3d Days, %02d:%02d:%02d" $DAYS $HOURS $MINS $SECS
   sleep 0.25
done

Exit on q:

while true; do
    echo -en "Press Q to exit \t\t: "
    read input
    if [[ $input = "q" ]] || [[ $input = "Q" ]] 
        then break 
    else 
        echo "Invalid Input."
    fi
done

PS: I'm very new to this.

score 13 · Accepted Answer · 2016-10-06 22:02:27Z

Maybe this helps you. I integrated both of them, with slight modifications though. Here's the result.

BEGIN=$(date +%s)

echo Starting Stopwatch...
echo Press Q to exit.

while true; do
    NOW=$(date +%s)
    let DIFF=$(($NOW - $BEGIN))
    let MINS=$(($DIFF / 60))
    let SECS=$(($DIFF % 60))
    let HOURS=$(($DIFF / 3600))
    let DAYS=$(($DIFF / 86400))

    # \r  is a "carriage return" - returns cursor to start of line
    printf "\r%3d Days, %02d:%02d:%02d" $DAYS $HOURS $MINS $SECS

# In the following line -t for timeout, -N for just 1 character
    read -t 0.25 -N 1 input
    if [[ $input = "q" ]] || [[ $input = "Q" ]]; then
# The following line is for the prompt to appear on a new line.
        echo
        break 
    fi
done

As you can see, I put the second script in place of the sleep command in the former first one. The time-out in read now bears the time lapse function. Notice that the -N option is needed for read not to wait for Enter and react as soon as the first key has been pressed.

Barry · Accepted Answer · 2021-11-18 08:29:27Z

2

I prefer the more concise until...

until read -s -n 1 -t 0.01; do 
    echo -n "."
    sleep .5
    done 
echo

The only minor issue is the single character being shown.

edited Nov 18, 2021 at 8:29

Barry

1033 bronze badges

answered Sep 30, 2021 at 21:11

Martin R

1234 bronze badges

Add a comment |

Community · Accepted Answer · 2017-05-23 12:39:56Z

Inpired from this answer, you can use read with the -t option, so that it only waits for a specified time, and not indefinitely. The code below combines the two snippets you posted:

#!/bin/bash

begin=$(date +%s)
echo "Starting Stopwatch... Press q to exit"
while true; do
   now=$(date +%s)
   diff=$(($now - $begin))
   mins=$(($diff / 60))
   secs=$(($diff % 60))
   hours=$(($diff / 3600))
   days=$(($diff / 86400))

   # \r  is a "carriage return" - returns cursor to start of line
   # with \33[2K we clear the current line
   printf "\33[2K\r%3d Days, %02d:%02d:%02d" $days $hours $mins $secs

   # -n 1 to get one character at a time, -t 0.1 to set a timeout 
   read -n 1 -t 0.1 input                  # so read doesn't hang
   if [[ $input = "q" ]] || [[ $input = "Q" ]] 
   then
      echo # to get a newline after quitting
      break
   fi
done

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