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The recode reference manual

13.5 Artificial data for testing

A few pseudo-surfaces exist to generate debugging data out of thin air. These surfaces are only meant for the expert recode user, and are only useful in a few contexts, like for generating binary permutations from the recoding or acting on them.

Debugging surfaces, when removed, insert their generated data at the beginning of the output stream, and copy all the input stream after the generated data, unchanged. This strange removal constraint comes from the fact that debugging surfaces are usually specified in the before position instead of the after position within a request. With debugging surfaces, one often recodes file `/dev/null' in filter mode. Specifying many debugging surfaces at once has an accumulation effect on the output, and since surfaces are removed from right to left, each generating its data at the beginning of previous output, the net effect is an impression that debugging surfaces are generated from left to right, each appending to the result of the previous. In any case, any real input data gets appended after what was generated.

test7

When removed, this surface produces 128 single bytes, the first having value 0, the second having value 1, and so forth until all 128 values have been generated.

test8

When removed, this surface produces 256 single bytes, the first having value 0, the second having value 1, and so forth until all 256 values have been generated.

test15

When removed, this surface produces 64509 double bytes, the first having value 0, the second having value 1, and so forth until all values have been generated, but excluding risky UCS-2 values, like all codes from the surrogate UCS-2 area (for UTF-16), the byte order mark, and values known as invalid UCS-2.

test16

When removed, this surface produces 65536 double bytes, the first having value 0, the second having value 1, and so forth until all 65536 values have been generated.

As an example, the command `recode l5/test8..dump < /dev/null' is a convoluted way to produce an output similar to `recode -lf l5'. It says to generate all possible 256 bytes and interpret them as ISO-8859-9 codes, while converting them to UCS-2. Resulting UCS-2 characters are dumped one per line, accompanied with their explicative name.