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From: Chad on 3 Jun 2010 13:15 On Jun 2, 9:11 pm, Bit Twister <BitTwis...(a)mouse-potato.com> wrote: > On Wed, 2 Jun 2010 19:26:37 -0700 (PDT), Chad wrote: > > What's the difference between > > > % w | wc -l > > 33 > > > versus something like.. > > > % wc -l <(w) > > 33 /tmp/zshx9eHyc > > % > > /tmp/zshx9eHyc > > > I mean, they both give the same results. Is there any particular > > advantage of using one over the other? > > Both seem inefficient to me. I would do something like > > line_count=$(wc -l < /some/file) How do you figure the following is more efficient. line_count=$(wc -l < /some/file)
From: Barry Margolin on 3 Jun 2010 22:04 In article <7ee000c8-e076-4dde-b686-2ac66b69504b(a)v29g2000prb.googlegroups.com>, Chad <cdalten(a)gmail.com> wrote: > On Jun 2, 7:54�pm, Barry Margolin <bar...(a)alum.mit.edu> wrote: > > In article > > <b0e62205-3ba2-491c-991b-d51d15ca0...(a)s6g2000prf.googlegroups.com>, > > > > �Chad <cdal...(a)gmail.com> wrote: > > > What's the difference between > > > > > % w | wc -l > > > � � � 33 > > > > > versus something like.. > > > > > % wc -l <(w) > > > � � � 33 /tmp/zshx9eHyc > > > % > > > > > I mean, they both give the same results. Is there any particular > > > advantage of using one over the other? > > > > As you can see, they don't actually give the same results. �In one case, > > wc is given a filename parameter, so it displays the filename in its > > output; in the other case, it's reading from stdin, so there's no > > filename to display. > > > > <(...) is generally used in situations where ordinary piping won't fork. � > > For instance, I've used it with programs that take multiple file > > arguments and process them together, rather than sequentially, e.g. > > > > diff <(...) <(...) > > > > What are some situations where ordinary piping won't fork? Oops, I meant "won't work". What a crazy typo, it still makes sense in context, so the error isn't immediately obvious, but what it states is definitely wrong. -- Barry Margolin, barmar(a)alum.mit.edu Arlington, MA *** PLEASE post questions in newsgroups, not directly to me *** *** PLEASE don't copy me on replies, I'll read them in the group ***
From: Barry Margolin on 3 Jun 2010 22:07 In article <slrni0eaqs.8rc.BitTwister(a)cooker.home.test>, Bit Twister <BitTwister(a)mouse-potato.com> wrote: > On Wed, 2 Jun 2010 19:26:37 -0700 (PDT), Chad wrote: > > What's the difference between > > > > % w | wc -l > > 33 > > > > versus something like.. > > > > % wc -l <(w) > > 33 /tmp/zshx9eHyc > > % > > > > /tmp/zshx9eHyc > > > I mean, they both give the same results. Is there any particular > > advantage of using one over the other? > > Both seem inefficient to me. I would do something like > > line_count=$(wc -l < /some/file) Don't you first have to get the output of "w" into /some/file? Isn't that less efficient, since it has to write to disk? Also, it prevents w and wc from being run in parallel, you can't start wc until after w executes. -- Barry Margolin, barmar(a)alum.mit.edu Arlington, MA *** PLEASE post questions in newsgroups, not directly to me *** *** PLEASE don't copy me on replies, I'll read them in the group ***
From: Bit Twister on 3 Jun 2010 22:14 On Thu, 03 Jun 2010 22:07:44 -0400, Barry Margolin wrote: > Don't you first have to get the output of "w" into /some/file? Isn't > that less efficient, since it has to write to disk? True, I just saw the | wc -l and without checking what was going on showed you can use wc < whatever without using the pipe operator. My Bad. Sorry.
From: Ben Finney on 3 Jun 2010 22:41
Barry Margolin <barmar(a)alum.mit.edu> writes: > Chad <cdalten(a)gmail.com> wrote: > > What are some situations where ordinary piping won't fork? > > Oops, I meant "won't work". What a crazy typo, it still makes sense in > context, so the error isn't immediately obvious, but what it states is > definitely wrong. Freud would be proud :-) -- \ “Natural catastrophes are rare, but they come often enough. We | `\ need not force the hand of nature.” —Carl Sagan, _Cosmos_, 1980 | _o__) | Ben Finney |