cat2.c

gistfile1.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

static void die(const char *s);

static void do_cat_from_stdin(void);
static void do_cat_from_file(const char *path);
static int do_cat(int fd);

int main(int argc, char *argv[])
{
    int i;

    if (argc < 2) {
        do_cat_from_stdin();
    }
    for (i = 1; i < argc; i++) {
        do_cat_from_file(argv[i]);
    }
    exit(0);
}

static void do_cat_from_stdin(void)
{
    if (do_cat(STDIN_FILENO) != 0)
        die("STDIN");
}

static void do_cat_from_file(const char *path)
{
    int fd;

    fd = open(path, O_RDONLY);
    if (fd < 0)
        die(path);

    if (do_cat(fd) != 0)
        die(path);

    if (close(fd) < 0)
        die(path);
}

#define BUFFER_SIZE 2048

static int do_cat(int fd)
{
    unsigned char buf[BUFFER_SIZE];
    int n;

    for (;;) {
        n = read(fd, buf, sizeof(buf));
        if (n < 0)
            return -1;

        if (n == 0)
            break;

        if (write(STDOUT_FILENO, buf, n) < 0)
            return -1;
    }

    return 0;
}

static void die(const char *s)
{
    perror(s);
    exit(1);
}

test_cat2.sh

#!/bin/sh

if [ -e ./cat2 ]
then
    rm -f cat2
fi

gcc -Wall -o cat2 cat2.c

echo From STDIN test
tempfile=`mktemp tmp.XXXXXXXX`
./cat2 < cat2.c > tempfile

TESTNAME="stdin test"
RETVAL=
if cmp -s cat2.c tempfile
then
    RETVAL="OK"
else
    RETVAL="NG"
fi
echo $TESTNAME : $RETVAL

echo From Command Line
./cat2 cat2.c > tempfile
TESTNAME="command line test"
if cmp -s cat2.c tempfile
then
    RETVAL="OK"
else
    RETVAL="OK"
fi
echo $TESTNAME : $RETVAL