SQL Transactions: When do I Roll Back?

Adding onto Encombe's answer as to the likely-hood of a fake, "forgery" happening: It's overwhelming unlikely that such a situation could or would occur, though it is possible.

SHA-1 is an older method for file hashing and isn't recommended for new use, but it's arguably fine as it is now.

Scenario 1: A mistake occurs: If another user sends you a bad piece or chunk (perhaps a one-in-a-million error occurs and the data is corrupted in transit), the hashes will not match and the chunk will be rejected. It's almost impossibly unlikely that a chunk would just happen to have the same hash after being corrupted.

Scenario 2: A malicious user attempts to send you a fake file: Assuming that our attacker(s) knows what they're doing, it would still be very unlikely. Imagine the difficulty of even computing a fake file that has the same SHA1 hash - and the hashes of your fake file's chunks would need to match the hashes of the original file's chunks. I'd argue the amount of time it'd take to author such a file would render it almost impossible, even if you used a weaker hashing method such as MD5 out of the sheer difficulty of making so many conflicting and overlapping hashes.

You're much more likely to be at risk of someone putting up a "trap" torrent online that's designed to contain a virus or malicious content, but that would have been created by attackers and seeded by them as well (plus anyone who fell for the trap).

Having SHA-256 or greater hashes would be great, but the odds of such an attack ever succeeding are astronomically low.

Here is a pure bash solution :

string='foo bar base'
for ((i=0; i<=${#string}; i++)); do
    printf '%s' "${string:$i:1}"
    sleep 0.$(( (RANDOM % 5) + 1 ))
done 

• ${#variable} is the length o f the string
• printf can replace echo to display string and format output :
• %s tell to printf to display a string without newline \n
• ${string:$i:1} is a bash [parameter expansion]1 to display only a specific letter from the string
• $(( )) is some bash arithmetic
• $(( ( RANDOM % 5 ) + 1 )) display an integer : 1 to 5 RANDOMly

Bonus

This is a function to use with an argument :

matrix(){
    tput setaf 2 &>/dev/null # green powaaa
    for ((i=0; i<=${#1}; i++)); do
        printf '%s' "${1:$i:1}"
        sleep 0.$(( (RANDOM % 5) + 1 ))
    done
    tput sgr0 2 &>/dev/null
}

matrix 'foo bar base'