# Difference between command substitution joined with cat and joined with joyn

The script `stepped-countup.sh` is a counter that counts up in step increments.

The arguments are the label of the counter, the time to be measured by the counter and the interval for display.

```sh
$ ./stepped-countup.sh a 10 2
a 0
a 2
a 4
a 6
a 8
a done.
```

Running two counters simultaneously and displaying the counts will result in an interleaved display, as shown below.

```sh
$ ./stepped-countup.sh a 10 2 & ./stepped-countup.sh b 9 3
[1] 192222
b 0
a 0
a 2
b 3
a 4
b 6
a 6
a 8
b done.
a done.
```

When run two counters using bash process substitution and the `cat` command, the output is the same as when the counters are run sequentially in order as the arguments of the `cat` command.

```sh
$ cat <(./stepped-countup.sh a 10 2) <(./stepped-countup.sh b 9 3)
a 0
a 2
a 4
a 6
a 8
a done.
b 0
b 3
b 6
b done.
```

On the other hand, when the `joyn` command is used, the output is similar to when two counters are run in parallel.

```sh
$ joyn <(./stepped-countup.sh a 10 2) <(./stepped-countup.sh b 9 3)
a 0
b 0
a 2
b 3
a 4
b 6
a 6
a 8
b done.
a done.
```

The command lines with `cat` and `joyn` shown above also differ in the timing of printing each line of the output. Please check by actually running the command lines.