macos - How to extract two numbers from two strings and calculate the difference in Bash?

I have a text file which contains (among others) the following lines:

{chapter}{{1}Einleitung}{27}{chapter.1}  
{chapter}{{2}Grundlagen}{35}{chapter.2}

How can I

• get the 2 lines from this text file (they will always contain }Einleitung resp. }Grundlagen} and


• extract the 2 page numbers (in this case 27 and 35),


• calculate the difference 35-27 = 8 and


• save the difference (8) of the two numbers in a variable

Perhaps with a bash script in Mac OS X?

Answer

I do not know if Mac OS X has awk. If it does, this should work:

This should work:

DIFFERENZ=$(awk 'BEGIN {
  FS="[{}]+"
 } {
  if ($4=="Einleitung")
   EINLEITUNG=$5
  if ($4=="Grundlagen")
   GRUNDLAGEN=$5
 } END {
   print GRUNDLAGEN-EINLEITUNG
 }' textfile)

How it works:

• FS="[{}]+" sets the field separator to any combination of curly brackets.


• $4 refers to the third filed on the line (separated by curly brackets).


• DIFFERENZ=$(...) evaluates the command ... and stores the ouput in DIFFERENZ.