Convert JSON lines to JSON array using jq

Maybe, I am late but this is what you are looking for!

jq -s '.' in.json > out.json

It looks like inputs suffers from the same issue as slurp. I don't know how to accomplish this with jq on huge files, but sed can do it:

sed '1s/^/[/; $!s/$/,/; $s/$/]/' in.json > out.json

Output:

[{"Header":{"AssetClass":"Commodities","InstrumentType":"Forward","UseCase":"Forward","Level":"InstRefDataReporting"},"Attributes":{"NotionalCurrency":"EUR","ExpiryDate":"2018-01-01","ReturnorPayoutTrigger":"Contract for Difference (CFD)","DeliveryType":"CASH","BaseProduct":"AGRI","TransactionType":"FUTR","FinalPriceType":"ARGM","ReferenceRate":"10PPM ULTRA LOW SULPHUR DIESEL-CARGOES CIF NWE/BASIS ARA-PLATTS EUROPEAN","SubProduct":"GROS","AdditionalSubProduct":"FWHT"},"ISIN":{"ISIN":"EZX27M86B860","Status":"New"},"TemplateVersion":1,"Derived":{"CommodityDerivativeIndicator":"TRUE","UnderlyingAssetType":"Agriculture","IssuerorOperatoroftheTradingVenueIdentifier":"NA","PriceMultiplier":1,"FullName":"Commodities Forward AGRI GROS FWHT EUR 20180101","ShortName":"NA/Fwd AGRI FWHT EUR 20180101","ClassificationType":"JTAXCC"}},{"Header":{"AssetClass":"Commodities","InstrumentType":"Swap","UseCase":"Basis_Swap","Level":"InstRefDataReporting"},"Attributes":{"NotionalCurrency":"SOS","ExpiryDate":"2208-12-10","ReturnorPayoutTrigger":"Total Return","DeliveryType":"OPTL","TransactionType":"ORIT","FinalPriceType":"IHSM","ReferenceRate":"NATURAL GAS-MONTHLY INDEX S. TEXAS (TETCO)-GAS DAILY PRICE GUIDE","OtherReferenceRate":"NATURAL GAS-MONTHLY INDEX W. LOUISIANA (TETCO)-GAS DAILY PRICE GUIDE","BaseProduct":"OTHR","OtherBaseProduct":"OTHR","SubProduct":"","AdditionalSubProduct":"","OtherSubProduct":"","OtherAdditionalSubProduct":""},"ISIN":{"ISIN":"EZBBH1XR9GV6","Status":"New"},"TemplateVersion":1,"Derived":{"CommodityDerivativeIndicator":"TRUE","UnderlyingAssetType":"Multi Commodity","IssuerorOperatoroftheTradingVenueIdentifier":"NA","PriceMultiplier":1,"FullName":"Commodities Swap Basis_Swap OTHR   OTHR   SOS 22081210","ShortName":"NA/Swap OTHR   SOS 22081210","ClassificationType":"STQTXE"}},{"Header":{"AssetClass":"Commodities","InstrumentType":"Swap","UseCase":"Multi_Exotic_Swap","Level":"InstRefDataReporting"},"Attributes":{"NotionalCurrency":"LRD","ExpiryDate":"2200-01-31","ReturnorPayoutTrigger":"Contract for Difference (CFD)","DeliveryType":"CASH","TransactionType":"TAPO","FinalPriceType":"EXOF","UnderlyingInstrumentIndex":["BCOMF6","BCOMNG3"]},"ISIN":{"ISIN":"EZ286HJVY4Q2","Status":"New"},"TemplateVersion":1,"Derived":{"CommodityDerivativeIndicator":"TRUE","IssuerorOperatoroftheTradingVenueIdentifier":"NA","PriceMultiplier":1,"UnderlyingAssetType":"Multi Commodity","BaseProduct":"MCEX","SubProduct":"","AdditionalSubProduct":"","FullName":"Commodities Multi_Exotic_Swap MCEX LRD 22000131","ShortName":"NA/Swap MCEX LRD 22000131","ClassificationType":"STQCXC"}},{"Header":{"AssetClass":"Commodities","InstrumentType":"Option","UseCase":"Option","Level":"InstRefDataReporting"},"Attributes":{"NotionalCurrency":"TND","ExpiryDate":"2209-10-18","OptionType":"OPTL","OptionExerciseStyle":"AMER","ValuationMethodorTrigger":"Asian","DeliveryType":"CASH","TransactionType":"OTHR","FinalPriceType":"IHSM","ReferenceRate":"NATURAL GAS-NGPL (NICOR, NIPSCO, PGLC CITYGATE), NBPL-NICOR-ICE/10X MONTHLY","BaseProduct":"OTHR","SubProduct":"","AdditionalSubProduct":""},"ISIN":{"ISIN":"EZ2TK5CWL9Y4","Status":"New"},"TemplateVersion":1,"Derived":{"CommodityDerivativeIndicator":"TRUE","UnderlyingAssetType":"Other","IssuerorOperatoroftheTradingVenueIdentifier":"NA","PriceMultiplier":1,"FullName":"Commodities Option OTHR   TND 22091018","ShortName":"NA/O OTHR  OPTL TND 22091018","ClassificationType":"HTMHAC"}},{"Header":{"AssetClass":"Commodities","InstrumentType":"Option","UseCase":"Multi_Exotic_Option","Level":"InstRefDataReporting"},"Attributes":{"NotionalCurrency":"SOS","ExpiryDate":"2209-10-18","UnderlyingInstrumentIndex":["BCOMSI2","BCOMPR3T"],"OptionType":"CALL","OptionExerciseStyle":"AMER","ValuationMethodorTrigger":"Other Path Dependent","DeliveryType":"CASH","TransactionType":"ORIT","FinalPriceType":"BLTC"},"ISIN":{"ISIN":"EZ82L36B6225","Status":"New"},"TemplateVersion":1,"Derived":{"CommodityDerivativeIndicator":"TRUE","IssuerorOperatoroftheTradingVenueIdentifier":"NA","PriceMultiplier":1,"UnderlyingAssetType":"Multi Commodity","BaseProduct":"MCEX","SubProduct":"","AdditionalSubProduct":"","FullName":"Commodities Multi_Exotic_Option MCEX SOS 22091018","ShortName":"NA/O MCEX Call SOS 22091018","ClassificationType":"HTQBPC"}}]

Explanation

The sed script consists of three separate substitutions. Here they are on separate lines:

1  s/^/[/      # Insert a left bracket at the beginning of the first line$! s/$/,/      # On all but the last line append a comma$  s/$/]/      # Append a right bracket to the last line

Maybe awk is easier on the eyes:

awk 'BEGIN{print "["}  length(last)>0 {print last ","} {last=$0} END {print last, "]"}'

And for the record, here's a slurp-free solution using a version of jq with input:

jq -nr '"[", try (input|tojson, repeat(",\n\(input|tojson)")), "]"'