Delete the first known character in a string with sed

How does one delete the first known character in a string with sed?

For example, say I want to delete the first character (which is @) in the string "@ABCDEFG1234"

I want sed to verify whether "@" exists as the first character. If so, it should delete the character.

sed 's/^@\(.*\)/\1/'

^ means beginning of the string

@ your known char

(.*) the rest, captured

then captured block will be substituted to output Sorry, can't test it at the moment, but should be something like that

There's no need to capture and replace.

sed 's/^@//'

This replaces the character @ when it's first ^ in the string, with nothing. Thus, deleting it.