2 added example
source | link

If you honestly want to use sed, then this is the way to go:

s/[0-9]/<&/g
s/0//g; s/1/|/g; s/2/||/g; s/3/|||/g; s/4/||||/g; s/5/|||||/g; s/6/||||||/g
s/7/|||||||/g; s/8/||||||||/g; s/9/|||||||||/g
: tens
s/|</<||||||||||/g
t tens
s/<//g
s/+//g
: minus
s/|-|/-/g
t minus
s/-$//
: back
s/||||||||||/</g
s/<\([0-9]*\)$/<0\1/
s/|||||||||/9/; s/||||||||/8/; s/|||||||/7/; s/||||||/6/; s/|||||/5/; s/||||/4/
s/|||/3/; s/||/2/; s/|/1/; s/<\([0-9]\)/<0\1/; s/<$/<0/
s/</|/g
t back

Input:

1+2
100+250
100-250

Output:

3
350
-150

Your mission, should you choose to accept it, is to implement multiplication.

If you honestly want to use sed, then this is the way to go:

s/[0-9]/<&/g
s/0//g; s/1/|/g; s/2/||/g; s/3/|||/g; s/4/||||/g; s/5/|||||/g; s/6/||||||/g
s/7/|||||||/g; s/8/||||||||/g; s/9/|||||||||/g
: tens
s/|</<||||||||||/g
t tens
s/<//g
s/+//g
: minus
s/|-|/-/g
t minus
s/-$//
: back
s/||||||||||/</g
s/|||||||||/9/; s/||||||||/8/; s/|||||||/7/; s/||||||/6/; s/|||||/5/; s/||||/4/
s/|||/3/; s/||/2/; s/|/1/; s/<\([0-9]\)/<0\1/; s/<$/<0/
s/</|/g
t back

Your mission, should you choose to accept it, is to implement multiplication.

If you honestly want to use sed, then this is the way to go:

s/[0-9]/<&/g
s/0//g; s/1/|/g; s/2/||/g; s/3/|||/g; s/4/||||/g; s/5/|||||/g; s/6/||||||/g
s/7/|||||||/g; s/8/||||||||/g; s/9/|||||||||/g
: tens
s/|</<||||||||||/g
t tens
s/<//g
s/+//g
: minus
s/|-|/-/g
t minus
s/-$//
: back
s/||||||||||/</g
s/<\([0-9]*\)$/<0\1/
s/|||||||||/9/; s/||||||||/8/; s/|||||||/7/; s/||||||/6/; s/|||||/5/; s/||||/4/
s/|||/3/; s/||/2/; s/|/1/
s/</|/g
t back

Input:

1+2
100+250
100-250

Output:

3
350
-150

Your mission, should you choose to accept it, is to implement multiplication.

1
source | link

If you honestly want to use sed, then this is the way to go:

s/[0-9]/<&/g
s/0//g; s/1/|/g; s/2/||/g; s/3/|||/g; s/4/||||/g; s/5/|||||/g; s/6/||||||/g
s/7/|||||||/g; s/8/||||||||/g; s/9/|||||||||/g
: tens
s/|</<||||||||||/g
t tens
s/<//g
s/+//g
: minus
s/|-|/-/g
t minus
s/-$//
: back
s/||||||||||/</g
s/|||||||||/9/; s/||||||||/8/; s/|||||||/7/; s/||||||/6/; s/|||||/5/; s/||||/4/
s/|||/3/; s/||/2/; s/|/1/; s/<\([0-9]\)/<0\1/; s/<$/<0/
s/</|/g
t back

Your mission, should you choose to accept it, is to implement multiplication.