# Bash runs on judgment.

The script reads one song per line on standard input and asks whether a Beatle wrote each one. It passes the question and its flags on the command line. `--true` and `--false` say what yes and no mean. `--threshold 0.2:0.8` sets the band. A probability of 0.8 or more is yes, and one under 0.2 is no. Between them is not sure. The two `--field` pointers send the title and the album as one JSON object. Without them, `decide` sends the whole line as text. The previous page keeps the same question in a file. The script plays a yes, skips a no, and hands a not sure to a person.

`decide --quiet` prints nothing. Its exit code is the answer: 0 for yes, 1 for no, and 3 for not sure. The function `is_original` names what the code means. `code=$?` names the code, and `case` picks the step. Any other code is a failure, and the script stops. [Handle not sure](/how-tos/bash/not-sure/) teaches the same form.

The numbers come from [the bench's songwriter list](https://github.com/botassembly/beatles-bench/blob/main/data/songs.tsv).

*setlist.sh, the script*

```
is_original() {
  thinkthen decide 'Did a Beatle write this song?' \
    --true 'John, Paul, George, or Ringo wrote it.' \
    --false 'Someone else wrote it. It is a cover.' \
    --threshold 0.2:0.8 --quiet \
    --field /title --field /album
}
while read -r song; do
  title=$(printf '%s\n' "$song" | jq -r .title)
  printf '%s\n' "$song" | is_original
  code=$?
  case $code in
    0) echo "play   $title" ;;
    1) echo "skip   $title" ;;
    3) echo "check  $title" ;;
    *) exit "$code" ;;
  esac
done
```

*setlist.jsonl, the songs, one JSON record per line*

```
{"title":"Something","album":"Abbey Road"}
{"title":"Act Naturally","album":"Help!"}
{"title":"Words of Love","album":"Beatles for Sale"}
{"title":"Mr. Moonlight","album":"Beatles for Sale"}
```

## Run it

*The run feeds setlist.jsonl to the script. Two songs play, one is skipped, and one goes to a person.*

```
bash setlist.sh < setlist.jsonl
```

*Output*

```
play   Something
skip   Act Naturally
play   Words of Love
check  Mr. Moonlight
```

*exit 0*

## The lesson

Two of the three sure answers are right. Jev says a Beatle wrote Words of Love. Buddy Holly wrote it. Mr. Moonlight falls inside the band, and a person checks it. Roy Lee Johnson wrote it.

The exit code is the answer, and an ordinary `case` acts on it.

On GitHub: [github.com/botassembly/beatles-bench](https://github.com/botassembly/beatles-bench)