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A standard approach could be:

what_we_want='123456789'
context='firstname'
distance=10
grep -E -e "${context}" -C "${distance}" file_to_look_into | grep -E -e "${what_we_want}" -C "${distance}"

The first ensure that we only look $distance lines around $context matching lines, the 2nd then see if it find "$what_we_want" in those 2*$distance+1 lines. If you just want the matching line as a result, drop the -C "${distance}" from the 2nd grep.

A standard approach could be:

what_we_want='123456789'
context='firstname'
distance=10
grep -E -e "${context}" -C "${distance}" file_to_look_into | grep -E -e "${what_we_want}" -C "${distance}"

The first grep ensures that we only look $distance lines around $context matching lines. The 2nd then sees if it find $what_we_want in those 2*$distance+1 lines.

If you just want the matching line as a result, drop the -C "${distance}" from the 2nd grep.

A standard approach could be:

what_we_want='123456789'
context='firstname'
distance=10
grep -E -e "${context}" -C "${distance}" file_to_look_into | grep -E -e "${what_we_want}" -C "${distance}"
# the first ensure that we only look $distance lines around $context matching lines, 
# the 2nd then see if it find "$what_we_want" in those 2*$distance+1 lines.
# if you just want the matching line as a result, drop the -C "${distance}" from the 2nd grep.

A standard approach could be:

what_we_want='123456789'
context='firstname'
distance=10
grep -E -e "${context}" -C "${distance}" file_to_look_into | grep -E -e "${what_we_want}" -C "${distance}"

The first ensure that we only look $distance lines around $context matching lines, the 2nd then see if it find "$what_we_want" in those 2*$distance+1 lines. If you just want the matching line as a result, drop the -C "${distance}" from the 2nd grep.

A standard approach could be:

what_we_want='123456789'
context='firstname'
distance=10
grep -E "${context}" -C "${distance}" file_to_look_into | grep -E "${what_we_want}" -C "${distance}"
# the first ensure that we only look $distance lines around $context matching lines, 
# the 2nd then see if it find "$what_we_want" in those 2*$distance+1 lines.
# if you just want the matching line as a result, drop the -C "${distance}" from the 2nd grep.

A standard approach could be:

what_we_want='123456789'
context='firstname'
distance=10
grep -E -e "${context}" -C "${distance}" file_to_look_into | grep -E -e "${what_we_want}" -C "${distance}"
# the first ensure that we only look $distance lines around $context matching lines, 
# the 2nd then see if it find "$what_we_want" in those 2*$distance+1 lines.
# if you just want the matching line as a result, drop the -C "${distance}" from the 2nd grep.