I have the following output from Mathematica to C code:

$ cat file.txt
Complex(1.3, 2.7)*Power(kappa, 2.0) + Complex(0.3, 2.0)*Power(kappa,5.0)*log(alpha)

The file is extremely long (many tens of thousands of lines). I would like to replace every Complex(a, b) with (a + i*b) and every Power(a, b) to a^b. So the above sample would look like:

$ cat desired_file.txt
(1.3 + i*2.7)*kappa^2.0 + (0.3 + i*2.0)*kappa^5.0*log(alpha)

How can I use sed to achieve this result? It is not straight forward at all by reading regular expressions and examples out there.

How can I do this using sed?

  • Would the easiest solution not just be to create your own Complex and Power functions in Matlab? – Graeme Jun 28 '14 at 12:05

This should do it:

sed 's/Complex(\([^,]*\), *\([^)]*\))/(\1 + i*\2)/g; 
     s/Power(\([^,]*\), *\([^)]*\))/\1^\2/g' file

This will not work for nested statements like Power(Power(a, b), c).


  • To susbstitute patterns in sed, you use the substitution operator (s/pattern/replacement/). The g at the end means global, it causes the substitution to be applied to all matches.

  • Patterns can be captured and reused later by placing them inside escaped parentheses: \( and \). The first such pattern is \1, the second \2 etc.

  • To replace Complex(a, b), I use Complex(\([^,]*\), *\([^)]*\)). This means match Complex(, then the longest string of consecutive non-, characters ([^,]*) is captured as \1, then a single comma and zero or more spaces, then the longest string of non-) characters until the closing parenthesis is found. The whole thing is replaced with (\1 + i*\2).

  • The regular expression that matches the Power() is essentially the same.


You can use sed's string replace function:

sed -i 's/"complex(a, b)"/(a + i*b)/g'

The same for the other pattern, just replace complex(a,b) with the expression you want to replace and (a + i*b) with the string you want instead of that expression.

  • 1
    I think the OP is asking for the expression to replace. – terdon Jun 28 '14 at 13:02
  • @terdon sorry, I misunderstood something. – psimon Jun 28 '14 at 13:38

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