Modifying part of a string in bash script

Question

I have a file named variables.f90 , having many lines defining different variables, as follows ::

integer::n_monomer=6800 real*8::rx=5.0d0 #... randomly integer and real numbers defined real*8::mu_nano=8.0d0 ....... ...... 

and I dont know what will be the value of mu_nano, it can be any real number. Now I want to modify the above statement such that, its value is incremented by 1 using bash script as follows ::

real*8::mu_nano=9.0d0 

Answer 1

This looks like fortran code, and it is not the greatest idea ever to parse higher language source code, but anyway... with awk:

awk -F'[=.]' '/nano/{$2++; print $1"="$2"."$3; next}1' 

This assumes that variable is always given with a dot. It takes only integer part of it (between = and .), increase by 1, and prints everything back.

Answer 2

To edit in place, I'd use perl:

perl -i.bak -pe 's/(?<=mu_nano=)([\d.]+)/ sprintf "%.1f", $1+1 /e' variables.f90