output text doesn't return same results as json output

[ShawnTuatara]

Describe the bug

Wanting to get the first element in the list of CommandId based on the query I built. JSON output looks good initially and shows the two Ids. I add the | [0] to get the first element and that looks good with json output. Add --output text and the second id shows back up.

$ aws ssm list-commands --query "Commands[?starts_with(Comment,'Performance test')].CommandId" --filters "key=DocumentName,value=AWS-RunShellScript" "key=InvokedAfter,value=2025-01-01T00:00:00Z"
[
    "294cd794-d231-4d3f-9e2a-98a4594af415",
    "e31c41ce-6551-435e-ad89-eabe5fab2983"
]

$ aws ssm list-commands --query "Commands[?starts_with(Comment,'Performance test')].CommandId | [0]" --filters "key=DocumentName,value=AWS-RunShellScript" "key=InvokedAfter,value=2025-01-01T00:00:00Z"
"294cd794-d231-4d3f-9e2a-98a4594af415"

$ aws ssm list-commands --query "Commands[?starts_with(Comment,'Performance test')].CommandId | [0]" --filters "key=DocumentName,value=AWS-RunShellScript" "key=InvokedAfter,value=2025-01-01T00:00:00Z" --output text
294cd794-d231-4d3f-9e2a-98a4594af415
e31c41ce-6551-435e-ad89-eabe5fab2983

Regression Issue

• Select this option if this issue appears to be a regression.

Expected Behavior

The number of elements returned with text output matches the json output

Current Behavior

All elements are returned instead of only the first one

Reproduction Steps

Described in description.

Possible Solution

No response

Additional Information/Context

No response

CLI version used

2.17.29

Environment details (OS name and version, etc.)

aws-cli/2.17.29 Python/3.11.9 Linux/5.15.167.4-microsoft-standard-WSL2 exe/x86_64.ubuntu.24

[RyanFitzSimmonsAK]

Hi @ShawnTuatara, thanks for reaching out. This is expected and documented behavior.

The output type you specify changes how the --query option operates:

If you specify --output text, the output is paginated before the --query filter is applied, and the AWS CLI runs the query once on each page of the output. Due to this, the query includes the first matching element on each page which can result in unexpected extra output. To additionally filter the output, you can use other command line tools such as head or tail.

If you specify --output json, the output is completely processed as a single, native structure before the --query filter is applied. The AWS CLI runs the query only once against the entire structure, producing a filtered result that is then output.

If you have fewer than 50 (the page size limit of SSM ListCommands) commands, you could get around this by setting --page-size 50. Otherwise, you'll need to further filter the output as the note described or use --output json. Let me know if you have any follow-up questions.

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