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Speaking UNIX: Peering into pipes

Nov 04, 2009, 15:03 (0 Talkback[s])
(Other stories by Martin Streicher)


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"One of the cleverest and most powerful innovations in UNIX is the shell. It's more efficient than a GUI, and you can write scripts to automate many tasks. Better yet, the pipe operator assembles ad hoc programs right at the command line. The pipe chains commands in sequence, where the output of an earlier command becomes the input of a subsequent command.

"But the pipe has one major detractor: It's something of a black box. If you string commands together, the only evidence of progress is the output that the last command in the series generates. Yes, you can interject tee in the sequence, and you can watch an output file grow with tail, but those solutions work best once, lest the standard output (stdout) and standard error (stderr) of multiple phases commingle. Further, both solutions are crude indicators and likely mask how much computation each step requires.

"Of course, you could deconstruct a complex sequence into multiple individual steps, each with its own interim output file. And indeed, if you want to verify results at each interval, decomposition is ideal. Write a script, produce one data file for each step, use a data file between each pair of steps as input, and collect the final file as the ultimate result. However, such a practice is not well suited to the impromptu nature of the command line.

"What's needed is a progress meter that you can embed in the command line to measure throughput. Ideally, the meter could be repeated to benchmark each step—and because the sky's the limit, the tool would be open source and portable to multiple UNIX variants, such as Linux® and Mac OS X."

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