Bash: assignment of variable on same line not altering echo behavior [duplicate]

Question

a=2
a=3 echo $a     #prints 2

can someone explain why would anyone use the above code in line-2. a=3 will be ignored as there is no "enter" after it. But I saw it in script like above and not sure about the purpose.

Answer 1

$a is expanded by the shell (Bash) before a=3 is evaluated. So echo sees its argument as 2, which is what it prints. (If you set -x you can see that what gets executed is a=3 echo 2.)

var=val command is used to set an environment variable to be seen by command during its execution, but nowhere else. So when command reads environment variables (e.g. using getenv()), to it $var is val.

If echo were to look up $a while running, it would have the value 3.