type \Path\To\File
E.g.:
C:\> type .\a_file.txt
This is the file content...
C:\> set /p CONTENT=<C:\a_file.txt
C:\> echo %CONTENT%
This is the file content...
type \Path\To\File
E.g.:
C:\> type .\a_file.txt
This is the file content...
C:\> set /p CONTENT=<C:\a_file.txt
C:\> echo %CONTENT%
This is the file content...