vankuik.nl RecentChanges 2014-11-25 XML TXT

M4

Everyone seems to have forgotten about M4, an extremely handy standard Unix tool when you need a text file with some parts changed on a regular basis.

In a build process for example you often have text files which are the input for some specialized tool. These could be text files in XML for your object-relational mapping tool. These probably won't support some kind of variable input and this is where M4 comes in handy.

Create a file with the extension ".m4" containing macro's like these (mind the quotes!):

  define(`PREFIX', `jackv')

Then let M4 replace all instances of PREFIX:

  $ m4 mymacros.m4 orm-tool.xml

By default, m4 prints to the screen (standard output). Use the shell to redirect to a new file:

  $ m4 mymacros.m4 orm-tool.xml > personalized-orm-tool.xml

Sometimes, it's nice to define a macro based on an environment variable. That's possible too. The following command would suit your needs:

  [jackv@testbox1]$ m4 -DPREFIX="$USERNAME" mymacros.m4 orm-tool.xml

The shell will expand the variable $USERNAME and the -D option tells M4 that the macro PREFIX is defined as jackv.