How to copy a part of a line to another position

Question

I have about 100 print statements in a file like this:

printf("%f \n\n",row1.req_pnttime);

I want to copy the variable name inside the string so that it becomes like this

printf("row1.req_pnttime: %f \n\n",row1.req_pnttime);

Can anyone help me do this?

PS-The length of the variable name is different for every print statement so I need a generic way to do this.

Answer 1

sed 's/\(.*("\)\(.*,\)\(.*\))/\1\3: \2\3)/' /path/to/input.txt >/path/to/output.txt

Explanation

• The general format is sed 's/find/replace/'. i.e. find an expression and replace it.
• \( ... \) these are capturing groups. So anything that matches in between them is "captured" in a variable and can be recalled in the replace part, with \1, \2, \3, etc.
• So here, find \(.*("\)\(.*,\)\(.*\)).
  • Capturing group 1: .*(". Capture from the beginning to anything that ends with ("
  • Capturing group 2: .*,. From #1, capture up to ,.
  • Capturing group 3: .*. Capture up to (but not including) ).
• Then replace with the capturing groups and additional formatting \1\3: \2\3).