CODEWITHSUNDEEP
linuxbash
Scott Pearce
Scott Pearce

Reputation: 207

Change script output when key pressed while it is running in Bash

Is there a way to change the output of a script while it is running? Lets say I have a script called "numbers" and it is running. The script uses this loop to print numbers from 1 to 49:

for ((a=1; a<50; a++))
do
     echo $a
     sleep 1
done

How can I change the output of this loop while it is running? Let's say if I press a or b during the running, it should subtract 1 from the result.

Upvotes: 0

Views: 145

Answers (1)

kojiro
kojiro

Reputation: 77137

As noted in the comments there is no time to do anything during so short a run. But if I make the run longer and slower I can demonstrate something similar to what you're asking.

declare -i a b c # Ensure these values are treated as integers
b=1
for ((a=0; a < 10**6; a+=b)); do
    read -s -N1 -t.3 c && b=c
    printf '%d...' "$a"
done
echo

Breakdown of read arguments:

read -s   # Don't echo output
     -N1  # Read one character of input*
     -t.3 # Wait for .3 seconds before giving up
     c &&
b=c # If read was successful, assign value to c, then b

Here's some craziness. Enjoy:

declare -i a b
b=1
for ((a=0; a < 10**6; a+=b)); do
    if read -s -N1 -t.01 c; then
        case $c in
            j) b=b+1;;
            k) b=b-1;;
        esac
    fi
    printf '%d...' "$a"
done
echo

*I noticed that bash v3 seems to use read -n1 and v4 read -N1.

Upvotes: 2

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