Shell : logical ANDs and ORs instead of if-else

The {...} does not make a difference, so what you have is equivalent to this:

i=10[ $i -lt 5 ] && echo "$i < 5" ||[ $i -gt 5 ] &&echo "$i > 5" || [ $i -eq 5 ] &&echo "$i = 5"

And the way this works is:

1. [ $i -lt 5 ]: This is false (returns failure), so it jumps to the next ||, which has [ $i -gt 5 ] following it.

2. [ $i -gt 5 ]: This is true (returns success), so it jumps to the next &&, which has echo "$i > 5" following it.

3. echo "$i > 5": This returns success, so it jumps to the next &&, which has echo "$i = 5" following it.

4. echo "$i = 5": This returns success, so it jumps to... wait no, there's a newline. We're done.

&& and || are called short-circuit operators.

EDIT: To stress the point further,

A && B || C

is NOT the same as

if A; then    Belse    Cfi

It's equivalent to

if A; then    if ! B; then        C    fielse    Cfi

&& and || are evaluated from left to right. Your command is more or less equivalent to this:

(((( false && { echo 1; true; } ) || true ) && { echo 2; true; } ) || false ) && { echo 3; true; }

• false && { echo 1; true; } doesn't print anything, and evaluates to false
• false || true evaluates to true
• true && { echo 2; true; } prints 2 and evaluates to true
• true || false evaluates to true
• true && { echo 3; true; } prints 3 and evaluates to true.

Mystery solved.