$ pub outdated --json
{
  "packages": [
    {
      "package": "bar",
      "current": null,
      "upgradable": {
        "version": "1.2.3"
      },
      "resolvable": {
        "version": "2.0.0"
      },
      "latest": {
        "version": "2.0.0"
      }
    },
    {
      "package": "foo",
      "current": null,
      "upgradable": {
        "version": "1.2.3"
      },
      "resolvable": {
        "version": "1.2.3"
      },
      "latest": {
        "version": "1.2.3"
      }
    }
  ]
}

$ pub outdated --no-color
Dependencies  Current  Upgradable  Resolvable  Latest  
bar           -        *1.2.3      2.0.0       2.0.0   
foo           -        1.2.3       1.2.3       1.2.3   

dev_dependencies: all up-to-date

transitive dependencies: all up-to-date

transitive dev_dependencies: all up-to-date

No pubspec.lock found. There are no Current versions.
Run `pub get` to create a pubspec.lock with versions matching your pubspec.yaml.

1 dependency is constrained to a version that is older than a resolvable version.
To update it, edit pubspec.yaml.

$ pub outdated --no-color --up-to-date
Dependencies  Current  Upgradable  Resolvable  Latest  
bar           -        *1.2.3      2.0.0       2.0.0   
foo           -        1.2.3       1.2.3       1.2.3   

dev_dependencies: all up-to-date

transitive dependencies: all up-to-date

transitive dev_dependencies: all up-to-date

No pubspec.lock found. There are no Current versions.
Run `pub get` to create a pubspec.lock with versions matching your pubspec.yaml.

1 dependency is constrained to a version that is older than a resolvable version.
To update it, edit pubspec.yaml.

$ pub outdated --no-color --prereleases
Dependencies  Current  Upgradable  Resolvable  Latest  
bar           -        *1.2.3      2.0.0       2.0.0   
foo           -        1.2.3       1.2.3       1.2.3   

dev_dependencies: all up-to-date

transitive dependencies: all up-to-date

transitive dev_dependencies: all up-to-date

No pubspec.lock found. There are no Current versions.
Run `pub get` to create a pubspec.lock with versions matching your pubspec.yaml.

1 dependency is constrained to a version that is older than a resolvable version.
To update it, edit pubspec.yaml.

$ pub outdated --no-color --no-dev-dependencies
Dependencies  Current  Upgradable  Resolvable  Latest  
bar           -        *1.2.3      2.0.0       2.0.0   
foo           -        1.2.3       1.2.3       1.2.3   

transitive dependencies: all up-to-date

No pubspec.lock found. There are no Current versions.
Run `pub get` to create a pubspec.lock with versions matching your pubspec.yaml.

1 dependency is constrained to a version that is older than a resolvable version.
To update it, edit pubspec.yaml.

$ pub outdated --no-color --no-dependency-overrides
Dependencies  Current  Upgradable  Resolvable  Latest  
bar           -        *1.2.3      2.0.0       2.0.0   
foo           -        1.2.3       1.2.3       1.2.3   

dev_dependencies: all up-to-date

transitive dependencies: all up-to-date

transitive dev_dependencies: all up-to-date

No pubspec.lock found. There are no Current versions.
Run `pub get` to create a pubspec.lock with versions matching your pubspec.yaml.

1 dependency is constrained to a version that is older than a resolvable version.
To update it, edit pubspec.yaml.

$ pub outdated --no-color --mode=null-safety
Running in 'null safety' mode.
Showing packages where the current version doesn't fully support null safety.

Dependencies  Current  Upgradable  Resolvable  Latest  
bar           -        ✗1.2.3      ✗2.0.0      ✗2.0.0  
foo           -        ✗1.2.3      ✗1.2.3      ✗1.2.3  

dev_dependencies: all fully support null safety

transitive dependencies: all fully support null safety

transitive dev_dependencies: all fully support null safety

No pubspec.lock found. There are no Current versions.
Run `pub get` to create a pubspec.lock with versions matching your pubspec.yaml.

1 dependency is constrained to a version that is older than a resolvable version.
To update it, edit pubspec.yaml.

$ pub outdated --json --mode=null-safety
{
  "packages": [
    {
      "package": "bar",
      "current": null,
      "upgradable": {
        "version": "1.2.3",
        "nullSafety": false
      },
      "resolvable": {
        "version": "2.0.0",
        "nullSafety": false
      },
      "latest": {
        "version": "2.0.0",
        "nullSafety": false
      }
    },
    {
      "package": "foo",
      "current": null,
      "upgradable": {
        "version": "1.2.3",
        "nullSafety": false
      },
      "resolvable": {
        "version": "1.2.3",
        "nullSafety": false
      },
      "latest": {
        "version": "1.2.3",
        "nullSafety": false
      }
    }
  ]
}

$ pub outdated --json --no-dev-dependencies
{
  "packages": [
    {
      "package": "bar",
      "current": null,
      "upgradable": {
        "version": "1.2.3"
      },
      "resolvable": {
        "version": "2.0.0"
      },
      "latest": {
        "version": "2.0.0"
      }
    },
    {
      "package": "foo",
      "current": null,
      "upgradable": {
        "version": "1.2.3"
      },
      "resolvable": {
        "version": "1.2.3"
      },
      "latest": {
        "version": "1.2.3"
      }
    }
  ]
}