sed: Increment a number
1
1 7.3 Increment a Number
1 ======================
1
1 This script is one of a few that demonstrate how to do arithmetic in
1 'sed'. This is indeed possible,(1) but must be done manually.
1
1 To increment one number you just add 1 to last digit, replacing it by
1 the following digit. There is one exception: when the digit is a nine
1 the previous digits must be also incremented until you don't have a
1 nine.
1
1 This solution by Bruno Haible is very clever and smart because it
1 uses a single buffer; if you don't have this limitation, the algorithm
1 used in ⇒Numbering lines cat -n, is faster. It works by replacing
1 trailing nines with an underscore, then using multiple 's' commands to
1 increment the last digit, and then again substituting underscores with
1 zeros.
1
1 #!/usr/bin/sed -f
1
1 /[^0-9]/ d
1
1 # replace all trailing 9s by _ (any other character except digits, could
1 # be used)
1 :d
1 s/9\(_*\)$/_\1/
1 td
1
1 # incr last digit only. The first line adds a most-significant
1 # digit of 1 if we have to add a digit.
1
1 s/^\(_*\)$/1\1/; tn
1 s/8\(_*\)$/9\1/; tn
1 s/7\(_*\)$/8\1/; tn
1 s/6\(_*\)$/7\1/; tn
1 s/5\(_*\)$/6\1/; tn
1 s/4\(_*\)$/5\1/; tn
1 s/3\(_*\)$/4\1/; tn
1 s/2\(_*\)$/3\1/; tn
1 s/1\(_*\)$/2\1/; tn
1 s/0\(_*\)$/1\1/; tn
1
1 :n
1 y/_/0/
1
1 ---------- Footnotes ----------
1
1 (1) 'sed' guru Greg Ubben wrote an implementation of the 'dc' RPN
1 calculator! It is distributed together with sed.
1