4.2 Increment a Number

This script is one of a few that demonstrate how to do arithmetic in sed. This is indeed possible,(7) but must be done manually.

To increment one number you just add 1 to last digit, replacing it by the following digit. There is one exception: when the digit is a nine the previous digits must be also incremented until you don’t have a nine.

This solution by Bruno Haible is very clever and smart because it uses a single buffer; if you don’t have this limitation, the algorithm used in Numbering lines, is faster. It works by replacing trailing nines with an underscore, then using multiple s commands to increment the last digit, and then again substituting underscores with zeros.

#!/usr/bin/sed -f

/[^0-9]/ d

# replace all trailing 9s by _ (any other character except digits, could
# be used)
:d
s/9\(_*\)$/_\1/
td

# incr last digit only.  The first line adds a most-significant
# digit of 1 if we have to add a digit.

s/^\(_*\)$/1\1/; tn
s/8\(_*\)$/9\1/; tn
s/7\(_*\)$/8\1/; tn
s/6\(_*\)$/7\1/; tn
s/5\(_*\)$/6\1/; tn
s/4\(_*\)$/5\1/; tn
s/3\(_*\)$/4\1/; tn
s/2\(_*\)$/3\1/; tn
s/1\(_*\)$/2\1/; tn
s/0\(_*\)$/1\1/; tn

:n
y/_/0/

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