Understanding bash outputs when backgrounded jobs are not found When I enter the command: a&b I receive the output: [1] 15872 b: command not found a: command not found When I enter the command: a & c My terminal's output is: [2] 15964 c: command not found a: command not found [1] Exit 127 a [1] Exit 127 a and my text position flash thingy now appears in the preceding position (in addition to the usual "user_name@computer_name>" part) the string: [1]+ Exit 127 a What do the numbers in the output refer to?

Those numbers are most likely process IDs. It would help if you could elaborate on what you need to know exactly.