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Top Forums UNIX for Advanced & Expert Users Faster Concatenation of files Post 302123638 by jim mcnamara on Tuesday 26th of June 2007 10:45:31 AM
Old 06-26-2007
If the input files are all on the same physical disk/logical you are probably IO bound no matter what you do. Most of the time spent in any event is disk I/O wait time - especially if you are reading and writing to the same logical volume/physical disk.

If you can find a disk/logical volume that is not busy, then put your destination file there.

Otherwise, cat is pretty efficient - on HPUX 11i -
Code:
> time cat Cletr062606.txt > /dev/null

real    0m6.95s
user    0m0.01s
sys     0m0.28s

Most six seconds here is probably related to i/o wait time. The system was not busy at this time. /dev/null does not write to disk, so this is related to read wait times. This is for a 120MB file. My version of cat calls read with an 8192 byte buffer.
 

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pnmsplit(1)                                                   General Commands Manual                                                  pnmsplit(1)

NAME
pnmsplit - split a multi-image portable anymap into multiple single-image files SYNOPSIS
pnmsplit [pnmfile[ output_file_pattern]] DESCRIPTION
Reads a Netpbm file as input. Copies each image in the input into a separate file, in the same format. pnmfile is the file specification of the input file, or - to indicate Standard Input. The default is Standard Input. output_file_pattern tells how to name the output files. It is the file specification of the output file, except that the first occurence of "%d" in it is replaced by the image sequence number in unpadded ASCII decimal, with the sequence starting at 0. If there is no "%d" in the pattern, pnmsplit fails. The default output file pattern is "image%d". Note that to do the reverse operation (combining multiple single-image PNM files into a multi-image one), there is no special Netpbm pro- gram. Just use cat. SEE ALSO
pnm(5), cat(1) AUTHOR
Written by Bryan Henderson 19 June 2000 pnmsplit(1)
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