Use sed to convert roman numerals to arabic numerals

Question

I have text file format like this

SKI
SKII
SKIII
SKIV
SKV
SKVI
SKVII

I want to convert it with sed command into numerical. Can you help me out?

SK1
SK2
SK3
SK4
SK5
SK6
SK7

Thanks a lot!

Answer 1

There's no trivial way to do that. Brute force plus some care is required:

sed -e 's/SKIII/SK3/'  \
    -e 's/SKII/SK2/'   \
    -e 's/SKIV/SK4/'   \
    -e 's/SKVIII/SK8/' \
    -e 's/SKVII/SK7/'  \
    -e 's/SKVI/SK6/'   \
    -e 's/SKV/SK5/'    \
    -e 's/SKI/SK1/' "$@"

The longer sequences must precede the shorter ones, in general. And this only deals with 1-8; generalizing it is modestly hard.

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Actually the numbers are needed from 1 to 29. How can I deal with it? Same method?

If your forego the SK prefix, then with a little care, you do not need 29 separate -e expressions (though that would work, of course). This script will take you to 39 (tested to 31, the maximum number of days in a month); the extensions needed to get to 99 are fairly obvious, I believe (13 more -e expressions, I think). Note the special-case handling for numbers containing zeroes.

sed \
    -e 's/IX/9/'   \
    -e 's/XXX$/30/' \
    -e 's/XXX/3/'   \
    -e 's/XX$/20/' \
    -e 's/XX/2/'   \
    -e 's/X$/10/'  \
    -e 's/X/1/'    \
    -e 's/VIII/8/' \
    -e 's/VII/7/'  \
    -e 's/III/3/'  \
    -e 's/II/2/'   \
    -e 's/IV/4/'   \
    -e 's/VI/6/'   \
    -e 's/V/5/'    \
    -e 's/I/1/' "$@"