Thread: Inversion and the addition of characters in the sed

i have characters:

code:

1  2  3  4  5

i want in sed:

code:

a  1  b  2  b  3  b  4  b  5

i have written:

code:

echo -e '1\n2\n3\n4\n5' | sed -n -e '1!g;h;$p' -e '1a a' -e '2,$a b'

i received:

code:

a  b  b  b  5  4  3  2  1  b

bad result. me somebody?

code:

echo -e '1\n2\n3\n4\n5' |  sed -e 's|^1$|a\n1|;s|^\([1-4]\)$|\1\nb|'

if line '1', append 'a' before
if line '[1-4]', append 'b' after

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