How to change bash script output when the script is running?

Question

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

Answer 1

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