Could someone please explain why this works, specifically the fact that I am not using ‘$’ character before the names of the variables inside the if statement? I have searched the Bash Reference Manual, but could not find an explanation.
#!/usr/bin/env bash
one="$1"
two="$2"
three="$3"
four="$4"
if [[ one -le two ]] && [[ three -ge four ]]; then
echo "TRUE: $one <= $two && $three >= $four"
else
echo "FALSE: $one <= $two && $three >= $four"
fi
I have also tested it with for x1 in {1..3}; do for x2 in {1..3}; do for x3 in {1..3}; do for x4 in {1..3}; do ./test $x1 $x2 $x3 $x4; done; done; done; done |sort and it works perfectly.
>Solution :
In the description of Bash Conditional Expressions the description of the arithmetic comparison operators (-lt, -gt, etc.) says:
When used with the [[ command, Arg1 and Arg2 are evaluated as arithmetic expressions (see Shell Arithmetic).
And when you follow that link it says:
Within an expression, shell variables may also be referenced by name without using the parameter expansion syntax.
And the description of Arithmetic Expansion — $((expression)) says:
All tokens in the expression undergo parameter and variable expansion, command substitution, and quote removal. … The evaluation is performed according to the rules listed below (see Shell Arithmetic).