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up vote 1 down vote favorite

I have the following loop which counts from 0 till 99:

    #!/bin/bash

for ((i=0;i<100;i++));
do
   echo $i
   sleep 1
done

Is there a way to change the result of the output from terminal while this loop script is running. Lets say if I press letter k the loop automatically add 10 more number to the current number, so if we have 10 being displayed on the screen and we press K the loop should automatically change to 20! Thanks

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You could look at trap to trap certain signals or reading user input ( read command ) in your script and modify your script to act according to the input. –  rahul Apr 4 at 18:16

1 Answer 1

up vote 2 down vote accepted

As mentioned in comment you can use:

read -t 1 -n 1 key

which because of -t option we can remove sleep, so your script could be:

#!/bin/bash

for ((i=0; i<100; i++)); do
    read -t 1 -n 1 key
    if [ "$key" = "k" ]; then
        i=$((i + 10))
    fi
    echo $i
done

But I think more portable could be:

#!/bin/bash

if [ -t 0 ]; then stty -echo -icanon -icrnl time 0 min 0; fi

keystroke=''
i=0
while [ $i -lt 100 ]; do
    keystroke="$(dd bs=1 count=1 2>/dev/null)" # http://www.tldp.org/LDP/abs/html/
    if [ "$keystroke" = "k" ]; then
        i=$(( i + 10 ))
    elif [ "$keystroke" = "q" ]; then
        break
    fi
    i=$(( i + 1 ))
        echo $i
    sleep 1 
done

if [ -t 0 ]; then stty sane; fi

exit 0
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