Replace first symbol of sentence with capital letter

Question

I need help with capitalizing the first letter of the first word in sentences from an input file input.txt:

this is my first sentence. and this is the second sentence. that one is the third.

I want to make the output look like this in an output file output.txt:

This is my first sentence. And this is the second sentence. That one is the third.

Answer 1

bash version 4 way:

#!/usr/local/bin/bash

while IFS="." read -r -a line ; do
    for ((i=0; i<${#line[@]}; i++)) do
        if [[ $i > 0 ]]; then
            temp=$(echo ${line[$i]/ /})
            echo -n "${temp^}. "
        else
            echo -n "${line[$i]^}. "
        fi
    done
    echo
done < file