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Top Forums Shell Programming and Scripting Reading ALL BUT the first and last line of a huge file Post 302969963 by Scrutinizer on Wednesday 30th of March 2016 04:05:29 PM
Old 03-30-2016
Then I get these results:
Code:
$ time { read header; sed '$d'; } < greptestin1 > /dev/null

real	0m31.812s
user	0m30.796s
sys	0m0.658s

$ time { read header; perl -pe '{exit if eof}'; } < greptestin1 > /dev/null

real	0m20.205s
user	0m19.719s
sys	0m0.472s

$ time perl -ne 'print unless ($.==1 || eof)' greptestin1 > /dev/null

real	0m20.225s
user	0m19.600s
sys	0m0.490s

 

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read(9E)							Driver Entry Points							  read(9E)

NAME
read - read data from a device SYNOPSIS
#include <sys/types.h> #include <sys/errno.h> #include <sys/open.h> #include <sys/uio.h> #include <sys/cred.h> #include <sys/ddi.h> #include <sys/sunddi.h> int prefixread(dev_t dev, struct uio *uio_p, cred_t *cred_p); INTERFACE LEVEL
Architecture independent level 1 (DDI/DKI). This entry point is optional. PARAMETERS
dev Device number. uio_p Pointer to the uio(9S) structure that describes where the data is to be stored in user space. cred_p Pointer to the user credential structure for the I/O transaction. DESCRIPTION
The driver read() routine is called indirectly through cb_ops(9S) by the read(2) system call. The read() routine should check the valid- ity of the minor number component of dev and the user credential structure pointed to by cred_p (if pertinent). The read() routine should supervise the data transfer into the user space described by the uio(9S) structure. RETURN VALUES
The read() routine should return 0 for success, or the appropriate error number. EXAMPLES
Example 1 read() routine using physio() The following is an example of a read() routine using physio(9F) to perform reads from a non-seekable device: static int xxread(dev_t dev, struct uio *uiop, cred_t *credp) { int rval; offset_t off; int instance; xx_t xx; instance = getminor(dev); xx = ddi_get_soft_state(xxstate, instance); if (xx == NULL) return (ENXIO); off = uiop->uio_loffset; rval = physio(xxstrategy, NULL, dev, B_READ, xxmin, uiop); uiop->uio_loffset = off; return (rval); } SEE ALSO
read(2), write(9E), physio(9F), cb_ops(9S), uio(9S) Writing Device Drivers SunOS 5.11 19 Nov 1997 read(9E)
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