grep Simulation Using Only Unbuffered I/O

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Homework and Emergencies Homework & Coursework Questions grep Simulation Using Only Unbuffered I/O - C Post 302514697 by Corona688 on Sunday 17th of April 2011 02:27:59 PM

04-17-2011

Registered User

read() doesn't add NULLs to the end of your array, so checking for NULL won't work. read() DOES return how many bytes it read, so you could just stop there instead, but --

read() doesn't stop at the end of a line, either. You should read one by one and check for newlines yourself. You could try something like this:

Code:

// reads a line of text in a manner sort of like fgets, and adds null.
// returns the # of bytes read, 0 means error.
int my_getline(int fd, char *buf, int max)
{
        int n;
        // read until end of file, or newline, or max
        for(n=0; n<(max-1); n++)
        {
                 ssize_t b=read(fd, buf+n, 1); // read one byte
                 if(b <= 0) // end of file or error
                 {
                         buf[n]='\0'; // add null
                         return(n);
                 }
                 if(buf[n] == '\n') // end of line
                 {
                         buf[n+1]='\0'; // add null AFTER \n
                         return(n);
                 }
        }

        buf[n]='\0';
        return(n);
}

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LEARN ABOUT DEBIAN

bzfgrep

BZGREP(1)						      General Commands Manual							 BZGREP(1)

NAME

       bzgrep, bzfgrep, bzegrep - search possibly bzip2 compressed files for a regular expression

SYNOPSIS

       bzgrep [ grep_options ] [ -e ] pattern filename...
       bzegrep [ egrep_options ] [ -e ] pattern filename...
       bzfgrep [ fgrep_options ] [ -e ] pattern filename...

DESCRIPTION

       Bzgrep  is  used to invoke the grep on bzip2-compressed files. All options specified are passed directly to grep.  If no file is specified,
       then the standard input is decompressed if necessary and fed to grep.  Otherwise the given files are uncompressed if necessary and  fed	to
       grep.

       If  bzgrep  is  invoked as bzegrep or bzfgrep then egrep or fgrep is used instead of grep.  If the GREP environment variable is set, bzgrep
       uses it as the grep program to be invoked. For example:

	   for sh:  GREP=fgrep	bzgrep string files
	   for csh: (setenv GREP fgrep; bzgrep string files)

AUTHOR

       Charles Levert (charles@comm.polymtl.ca). Adapted to bzip2 by Philippe Troin <phil@fifi.org> for Debian GNU/Linux.

SEE ALSO

       grep(1), egrep(1), fgrep(1), bzdiff(1), bzmore(1), bzless(1), bzip2(1)

																	 BZGREP(1)

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