The unifdef utility selectively processes conditional C preprocessor #if and #ifdef directives. It removes from a file both the directives and the additional text that they delimit, while otherwise leaving the file alone.
It is useful for avoiding distractions when studying code that uses #ifdef heavily for portability (the original motivation was xterm's pty handling code), or as a lightweight preprocessor to strip out internal routines from a public header (the Linux kernel uses unifdef to strip out #ifdef __KERNEL__ sections from the headers it exports to userland).
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