Given a matrix stored as a tab-delimited file with row + col headers, the upper left entry is often blank (a single tab):

    A    B    C    D    E
A    1    1    1    1    1
B    1    1    1    1    1
C    1    1    1    1    1
D    1    1    1    1    1
E    1    1    1    1    1
[download]

I wish to be able to access and modify this entry. Ordinarily to access a specific element I would use something like:

perl -lanse 'print $F[$j-1] if $. == $i' -- -i=1 -j=1

However this prints 'A' and does not recognise the initial tab as counting as an element. Is there a way to print something into this first element? For example producing:

ID    A    B    C    D    E
A    1    1    1    1    1
B    1    1    1    1    1
C    1    1    1    1    1
D    1    1    1    1    1
E    1    1    1    1    1
[download]

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