Loop question

Hello,

I am trying to implement a simple loop. E.g. something like

repeat 100
command1
command2
endrepeat
command3
command1

The idea is to switch to an exclusive start state whenever "repeat" is match
ed. Then all commands of the repeat body should be expanded and written into
 a temporary file.
If "endrep" is matched, lex should return to the standard state.
Then the input files would have to be switched.

I am not sure about the switching. Maybe yacc could be used to set a global 
variable, too.

I aam trying to get familiar with lex/yacc, but loops seem to be quite hard.
 The O'Reilly book sort of skips this topic, too :-(

Any suggestions would be highly appreciated!