ggm@brolga.cc.uq.oz.au (George Michaelson) (05/08/91)
I have written a very crude shellscript to do while loops over a read
command. This is to permit a user attached to a terminal that cannot
do control characters (!) to get access to unix and do some useful stuff
with MH and editors.
I have just found out she incurred around 300 seconds of CPU time on a
sun 4 in 1 login session.
simple tests using time on a shellscript of:
while 1
do
read INP
echo $INP
done
seem to suggest that read is incredibly expensive on the CPU.
Is this true, and is there any "cheaper" way to do interactive input
from a terminal within shellscripts?
Is this a "feature" in SunOS 4.1.1 /bin/sh?
-George
--
G.Michaelson
Internet: G.Michaelson@cc.uq.oz.au Phone: +61 7 365 4079
Postal: George Michaelson, the Prentice Centre,
The University of Queensland, St Lucia, QLD Australia 4072. allbery@NCoast.ORG (Brandon S. Allbery KB8JRR/AA) (05/11/91)
As quoted from <1991May8.013013.29811@brolga.cc.uq.oz.au> by ggm@brolga.cc.uq.oz.au (George Michaelson): +--------------- | simple tests using time on a shellscript of: | | while 1 | do | read INP | echo $INP | done | | seem to suggest that read is incredibly expensive on the CPU. +--------------- Do you know that it's "read" that is expensive? The other possibilities are: "while/do/done" and "echo". Not to mention that "while 1" returns "1: not found" on my system (admittedly, not a Sun 4), and the cost of interpolating and expanding the "echo" command line. A better test of the speed of "read" is to time a script containing only "read" statements. Also time an empty script so you can factor out the shell startup time, for still better accuracy. (Note: if your timing tests did in fact take this into account, you should probably have said so.) ++Brandon -- Me: Brandon S. Allbery Ham: KB8JRR/AA 10m,6m,2m,220,440,1.2 Internet: allbery@NCoast.ORG (restricted HF at present) Delphi: ALLBERY AMPR: kb8jrr.AmPR.ORG [44.70.4.88] uunet!usenet.ins.cwru.edu!ncoast!allbery KB8JRR @ WA8BXN.OH
heinz@cc.univie.ac.at (05/15/91)
allbery@NCoast.ORG (Brandon S. Allbery KB8JRR/AA) writes: >As quoted from <1991May8.013013.29811@brolga.cc.uq.oz.au> by ggm@brolga.cc.uq.oz.au (George Michaelson): >+--------------- >| simple tests using time on a shellscript of: >| >| while 1 >| do >| read INP >| echo $INP >| done >| >| seem to suggest that read is incredibly expensive on the CPU. >+--------------- >Do you know that it's "read" that is expensive? The other possibilities are: >"while/do/done" and "echo". Not to mention that "while 1" returns "1: not >found" on my system (admittedly, not a Sun 4), and the cost of interpolating >and expanding the "echo" command line. Well, "read" shouldn't consume too much CPU time, since it is essentially a blocking I/O operation and doesn't account to CPU consumption. What really *is* costly is the while/do/done. I've tried a while-loop in the GNU-bash on a SUN-3, where the loop body was a single "echo", and it put an awful load on the machine (actually, by running this loop simultaneously in several windows, you can prevent other people -and yourself- from doing anything useful :) Even a completely empty while-loop was sufficient to pose a significant delay on other jobs. So it is the shell itself that consumes the CPU time. -- Heinz Herbeck (heinz@sophie.pri.univie.ac.at)