I have a configure script to set up some paths for my R package during installation. I wish to edit a file based on some conditions. Is there any way to edit a file from within the configure.ac? It would be great if the solution is provided for all operating systems.
Is there any way to edit a file from within the configure.ac?
configure.ac is not executable, but I suppose you mean that you want the configure script generated from it to edit a file. The configure script is a shell script, and you can cause arbitrary shell code to be included in it, more or less just by including that code at the corresponding point in configure.ac.
The question, then, is how you would automate editing a file with a shell script. There is a variety of alternatives, but sed is high on my list. You will find it on every system that can support Autoconf configure scripts, because such scripts use it internally.
On the other hand, this sort of thing is one of the main activities of a configure script, in the form of creating files (especially makefiles, but not limited to those) from templates. You should consider building your target file of interest from a template in this way, instead of making custom-programmed edits to a file packaged in your program distribution. This would involve
configure to build; and@output_variable@.