Piping-content

ConvertFrom-Json pipeline input

ConvertFrom-Json accepts pipeline input but its help does not explain all the details. The straightforward scenario is

Get-Content data.json | ConvertFrom-Json

so that input strings are lines of a JSON file. Here is what tests cases show.

PowerShell v5

If the first line is empty then null is returned for it. Then all lines are joined and converted to an object. As a result, two objects are returned, the first null and the second converted object.

If the first line is not empty then it is converted to an object. If this fails then all lines are joined and converted into an object and a single object is returned. If the first conversion succeeds then the result object is returned and then each next line is converted into an object and returned with empty lines converted to nulls.

In other words,

• If a JSON file contains one object then avoid the first empty line, otherwise two objects are returned, the first is null. Alternatively, read the file as one string and then invoke ConvertFrom-Json with it.
• If a JSON file contains many objects then each object should be represented as one line. The first line must not be empty. Other empty lines should be avoided unless result nulls are expected by design.

PowerShell v4

Each line should represent an object. Empty lines are converted to nulls.

PowerShell v3

Not tested, feedback please.

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Scripts

• Test-1.multiline.object.ps1 works in v5, fails in v4
• Test-1.oneline.objects.ps1 works in v5, v4
• Test-2.multiline.object.empty.ps1 works with an issue in v5, fails in v4
• Test-2.oneline.objects.empty.ps1 works in v5, v4
• Test-3.multiline.objects.ps1 fails in v5, v4
• Test-3.oneline.objects.first.empty.ps1 fails in v5, works in v4