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cmd.exe - assoc
assoc allows to display or modify the associations between a filename extension (suffix) and its filetype.
The following command displays the filetype for the suffix .vbs:
C:\> assoc .vbs
.vbs=VBSFile
assoc can then be used to return a more friendly name for the filetype.
C:\> assoc VBSFile
VBSFILE=VBScript Script File
ftype can be used to reveal what program is used by default to start a file with a given extension:
C:\> ftype VBSFile
VBSFile="%SystemRoot%\System32\WScript.exe "%1" %*