what is the meaning of FOOBAR=foobar followed by a shell command? -

i see in shell scripts variable assignment followed (without semicolon) command. meaning of that? not seem affect command, , not seem affect next command way normal assignment would:

>echo $foobar  >foobar=1 echo $foobar  >echo $foobar  > 

so, does do?

it sets environment variable value process.

here, step step, happens:

• original command: foobar=1 echo $foobar
• shell performs substitution: command foobar=1 echo
• shell fork(2)s new process
• environment variable created in new process: command echo (with $foobar equal 1)
• new process exec(3)ed: \n output
• new process exits , reaped shell

at no point parent process see assigned value of $foobar.