ugh.book

162 csh, pipes, and find

Pipes are good for simple hacks, like passing around simple text streams,

but not for building robust software. For example, an early paper on pipes

showed how a spelling checker could be implemented by piping together

several simple programs. It was a tour de force of simplicity, but a horrible

way to check the spelling (let alone correct it) of a document.

Pipes in shell scripts are optimized for micro-hacking. They give program-

mers the ability to kludge up simple solutions that are very fragile. That’s

because pipes create dependencies between the two programs: you can’t

change the output format of one without changing the input routines of the

other.

Most programs evolve: first the program’s specifications are envisioned,

then the insides of the program are cobbled together, and finally somebody

writes the program’s output routines. Pipes arrest this process: as soon as

somebody starts throwing a half-baked Unix utility into a pipeline, its out-

put specification is frozen, no matter how ambigious, nonstandard, or inef-

ficient it might be.

Pipes are not the be-all and end-all of program communication. Our favor-

ite Unix-loving book had this to say about the Macintosh, which doesn’t

have pipes:

The Macintosh model, on the other hand, is the exact opposite. The

system doesn’t deal with character streams. Data files are extremely

high level, usually assuming that they are specific to an application.

When was the last time you piped the output of one program to

another on a Mac? (Good luck even finding the pipe symbol.) Pro-

grams are monolithic, the better to completely understand what you

are doing. You don’t take MacFoo and MacBar and hook them

together.

—From Life with Unix, by Libes and Ressler

Yeah, those poor Mac users. They’ve got it so rough. Because they can’t

pipe streams of bytes around how are they ever going to paste artwork from

their drawing program into their latest memo and have text flow around it?

How are they going to transfer a spreadsheet into their memo? And how

could such users expect changes to be tracked automatically? They cer-

tainly shouldn’t expect to be able to electronically mail this patched-

together memo across the country and have it seamlessly read and edited at

the other end, and then returned to them unscathed. We can’t imagine how

they’ve been transparently using all these programs together for the last 10

years and having them all work, all without pipes.