I know purists always complain about unnecessary cats, but I always find it useful to start with "head" or "tail" in the first position to figure out my pipeline, and then replace it with cat when it's all working.

And if the extra cat is actually making a measurable difference, maybe that's a good signal that it's time to rewrite it in C.

You can do with simple IO redirection. For example, the arbitrary pipeline

    $ cat data.txt | awk '{ print $2+$4,$0 }'|sort|sed '/^0/d'

can be written as

    $ <data.txt awk '{ print $2+$4,$0 }'|sort|sed '/^0/d'

Some people prefer the first, longer-winded way because it's more explicit. To some --- myself included --- it makes more sense because it explicitly breaks each function into a seperate steps; I'm explicitly telling the system to print the contents of data.txt rather than implictly doing so. I'll happily type those five extra characters for that additional clarity.