flash

#!/bin/sh
#
# flash - minimalistic flashcards for the terminal

# Parse command-line arguments. See also: `man getopts`.
while getopts hr opt; do
    case "$opt" in
        h)
            man 1 flash
            exit;;
        r)
            reverse=1;;
        ?)
            # Print help instructions to standard error and exit with code 2.
            printf "Try 'man flash' for more information.\n" >&2
            exit 2;;
    esac
done

# Read a line of input and split it on `FLASH_DELIMITER`, defaulting to `:`.
while IFS=${FLASH_DELIMITER:-':'} read q a; do
    # Remove leading whitespace.
    q="${q#${q%%[![:space:]]*}}"
    a="${a#${a%%[![:space:]]*}}"

    # Ignore blank lines.
    [ -z "$q" ] && [ -z "$a" ] && continue

    # Reverse the question order if the corresponding flag is set.
    [ "$reverse" = 1 ] && tmp=$q && q=$a && a=$tmp

    # Print the question.
    printf '%s' "$q"

    # Wait for user input, then print the answer. This initially attempts to
    # use non-POSIX features to improve ergonomics, but gracefully falls back
    # to POSIX compatibility mode on failure.
    if read -rsn 1 < /dev/tty 2> /dev/null; then
        printf '\n%s\n\n' "$a"
    else
        read -r _ < /dev/tty
        printf '%s\n\n' "$a"
    fi
done