read() wont allow me to read files larger than 2 gig (on a 64bit)


 
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Top Forums UNIX for Advanced & Expert Users read() wont allow me to read files larger than 2 gig (on a 64bit)
# 15  
Old 01-11-2010
For the third time, I'm sure you have. I'm sure they must be working on correcting the problem that prevents two-gig reads, as well; the sticky issue is likely how to manage that on 32-bit systems.

You weren't the OP, though, and my question was what these enormous reads were for in the first place. 9 out of 10 times I see someone sucking an enormous wad of raw data into RAM, they're not doing it for performance reasons -- they just want it all in RAM to get at it without further system calls. An mmap gets them that without decimating the cache and squeezing frequently-used things into swap for no good reason, and avoids this problem entirely.
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CAT(1)							      General Commands Manual							    CAT(1)

NAME
cat, read, nobs - catenate files SYNOPSIS
cat [ file ... ] read [ -m ] [ -n nline ] [ file ... ] nobs [ file ... ] DESCRIPTION
Cat reads each file in sequence and writes it on the standard output. Thus cat file prints a file and cat file1 file2 >file3 concatenates the first two files and places the result on the third. If no file is given, cat reads from the standard input. Output is buffered in blocks matching the input. Read copies to standard output exactly one line from the named file, default standard input. It is useful in interactive rc(1) scripts. The -m flag causes it to continue reading and writing multiple lines until end of file; -n causes it to read no more than nline lines. Read always executes a single write for each line of input, which can be helpful when preparing input to programs that expect line-at-a- time data. It never reads any more data from the input than it prints to the output. Nobs copies the named files to standard output except that it removes all backspace characters and the characters that precede them. It is useful to use as $PAGER with the Unix version of man(1) when run inside a win (see acme(1)) window. SOURCE
/src/cmd/cat.c /src/cmd/read.c /bin/nobs SEE ALSO
cp(1) DIAGNOSTICS
Read exits with status eof on end of file or, in the -n case, if it doesn't read nlines lines. BUGS
Beware of and which destroy input files before reading them. CAT(1)