如何解析存储在其中的字符串的php变量?

I'm new to php and am trying to parse a string I'm getting. The string is the result of a bash script I'm running, and I'm storing the output into a php variable. Here is the output I'm getting:

1/1 [==============================] - 1s 1s/step
[
  {
    "image_id": "mahomes1",
    "mean_score_prediction": 6.3682564571499825
  },
  {
    "image_id": "mahomes2",
    "mean_score_prediction": 6.7501190304756165
  },
  {
    "image_id": "mahomes3",
    "mean_score_prediction": 6.3136263862252235
  }, 
]

How would I go about parsing this string so that I can create a dictionary that stores the "image_id" value with the "mean_score_prediction" value?

Your data is almost valid JSON, other than the beginning text and the comma between the final } and closing ]. By cleaning those issues up, you can then use json_decode on it to get a dictionary as an array of objects (or arrays, dependent on your preference):

$string = preg_replace(array('/^[^\v]+/', '/,(\s+\])/'), array('', '$1'), $string);
$dict = json_decode($string);
print_r($dict);

Output:

Array ( 
  [0] => stdClass Object (
    [image_id] => mahomes1
    [mean_score_prediction] => 6.36825645715 
  )
  [1] => stdClass Object (
    [image_id] => mahomes2
    [mean_score_prediction] => 6.7501190304756
  )
  [2] => stdClass Object (
    [image_id] => mahomes3
    [mean_score_prediction] => 6.3136263862252
  ) 
)

To get an array of arrays, call json_decode with a second parameter of true i.e.

$dict = json_decode($string, true);

Demo on 3v4l.org