Concatenate multiple files with same header

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http://unix.stackexchange.com – I have multiple files with the same header and different vectors below that. I need to concatenate all of them but I want only the header of first file to be concatenated and I don't want other headers to be concatenated since they are all same. for example: file1.txt <header>INFO=<ID=DP,Number=1,Type=Integer> <header>INFO=<ID=DP4,Number=4,Type=Integer> A B C file2.txt <header>INFO=<ID=DP,Number=1,Type=Integer> <header>INFO=<ID=DP4,Number=4,Type=Integer> D E F I need the output to be <header>INFO=<ID=DP,Number=1,Type=Integer& (HowTos)