Let's start with a simple example of feeding our test application (we will call it "test_data") with zeroes, say 100 bytes with a value of zero.
head --bytes=100 /dev/zero | ./test_data
The above command has two parts; the first one (before the '|' delimiter), 'head', reads /dev/zero device, which provides us with zero-valued bytes as a stream, up to a count of 100 bytes and sends them to the second one, 'test_data', as input. If we wanted more, say 100 KBytes, we would replace the parameter of 'bytes' argument with "100k", as follows:
head --bytes=100k /dev/zero | ./test_data
Now, let's say we want random data. It's as simple as replacing '/dev/zero' device with '/dev/random':
head --bytes=100k /dev/random | ./test_data
With the above command combination, we produce 100 KBytes of random data as input to our test_data application.
And what if we wanted some specific data, like "testing with sample data", repeated 40 times?
yes "testing with sample data" | head -40 | ./test_data
The 'yes' command just outputs its input continuously; 'head' keeps only the first 40 lines; 'test_data' works with these 40 lines of the sample string.
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