Delete groups of lines that have the same first line, except for the first occurence

Question

This may be a couple questions in one, but this problem has me stuck. I have a text file with groupings of four lines separated by an empty line. The first line of every grouping begins with a '>' symbol. I want to delete all instances of groupings with identical first lines, except for the first instance of the grouping. First thing that comes to mind is using sed but cant think of a good way to implement. Would be grateful for any help!

input:

>abc1234.54321
linea1
lineaa1
lineaaa1

>def56789034
linea1
lineaa1
lineaaa1

>abc1234.54321
linea2
lineaa2
lineaaa2

>def56789034
linea2
lineaa2
lineaaa2

intended output:

>abc1234.54321
linea1
lineaa1
lineaaa1

>def56789034
linea1
lineaa1
lineaaa1

Answer 1

If you don't mind a possible additional trailing blank line, then Awk in paragrapgh mode will get you close:

$ awk -vRS= '!seen[$1]++' ORS='\n\n' input
>abc1234.54321
linea1
lineaa1
lineaaa1

>def56789034
linea1
lineaa1
lineaaa1

Unsetting the record separator (RS=) causes Awk to treat each group of blank-line-separated lines as a single record; then we use the value of an associative array keyed on the first field $1 to keep track of whether we have seen a record with this key before - if not (i.e. !seen[$1] is true) then print it.