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| -rw-r--r-- | README.md | 34 |
1 files changed, 27 insertions, 7 deletions
@@ -76,7 +76,33 @@ and go get it! this sort of thing can be useful in devops land. -## How about systems that have `awk` but no `cpp`? +8. `cppawk` has a `--prepro-only` option to generate the preprocessed + Awk program on standard output rather than execute it. This is useful + in several ways: + * debugging the inclusion process; + * preprocessing code on a machine with `cpp` to execute it on a system + which has no `cpp`. + * conditionally generating multiple programs from a single source + based on preprocessor symbols passed in via `-D` arguments. + +## But GNU Awk has `@include`? + +* GNU Awk's `@include` isn't a full preprocessor. There are no conditional + expressions, and no macros. + +* It is only implemented in GNU Awk. + +* It provides no way to capture all the included output. + +* The way `@include` searches for files is inferior to `cpp`. GNU Awk's include + search is driven by the `AWKPATH` variable which brings in all the + disadvantages shared by shared by `PATH`-like variables. + In contrast `cpp` implements the familiar behavior that an `#include "..."` + directive is resolved relative to the directory of the file which contains + that `#include` directive. No configuration is required for a program + to find all of its included pieces. + +## What about systems that have `awk` but no `cpp`? `cppawk` is used directly on systems that have `cpp`, as if it were an Awk implementation. @@ -85,9 +111,3 @@ it were an Awk implementation. which can be captured and transferred to a system that has no preprocessor installed, such as an embedded board that has BusyBox Awk. - -Of course, capturing the preprocessed output has other uses. -It's possible to generate different versions of an Awk program -by using `cppawk --prepro-only` in conjunction with conditional -preprocessing which reacts to different values of a macro defined -on the command line via `-D`. |