高级Linux程序设计第二章：编写良好的Linux软件_现有一命令行 program1 | program2, program1 和program2 为可执

% ls -s /

其参数列表包含三项：

第一项是程序名称ls，第二项和第三项分别是两个命令行参数，-s和/

#include

int main (int argc, char* argv[])

{

    printf (“The name of this program is ‘%s’./n”, argv[0]);

    printf (“This program was invoked with %d arguments./n”, argc - 1);

    /* Were any command-line arguments specified? */

    if (argc > 1) {

        /* Yes, print them. */

        int i;

        printf (“The arguments are:/n”);

        for (i = 1; i < argc; ++i)

            printf ("%s/n", argv[i]);

    }

    return 0;

}

短格式

长格式

目的

-h

--help

显示用法概要

-o filename

--output filename

指定输出文件名

-v

--verbose

打印详细信息

const struct option long_options[] = {

{ “help”, 0, NULL, ‘h’ },

{ “output”, 1, NULL, ‘o’ },

{ “verbose”, 0, NULL, ‘v’ },

{ NULL, 0, NULL, 0 }

};

#include

#include

#include

/* The name of this program. */

const char* program_name;

/* Prints usage information for this program to STREAM (typically stdout or stderr), and exit the program with EXIT_CODE. Does not return. */

void print_usage (FILE* stream, int exit_code)

{

    fprintf (stream, “Usage: %s options [ inputfile ... ]/n”, program_name);

    fprintf (stream,

        “ -h --help Display this usage information./n”

        “ -o --output filename Write output to file./n”

        “ -v --verbose Print verbose messages./n”);

    exit (exit_code);

}

/* Main program entry point. ARGC contains number of argument list elements; ARGV is an array of pointers to them. */

int main (int argc, char* argv[])

{

    int next_option;

    /* A string listing valid short options letters. */

    const char* const short_options = “ho:v”;

    /* An array describing valid long options. */

    const struct option long_options[] = {

    { “help”, 0, NULL, ‘h’ },

    { “output”, 1, NULL, ‘o’ },

    { “verbose”, 0, NULL, ‘v’ },

    { NULL, 0, NULL, 0 } /* Required at end of array. */

    };

    /* The name of the file to receive program output, or NULL for

    standard output. */

    const char* output_filename = NULL;

    /* Whether to display verbose messages. */

    int verbose = 0;

    /* Remember the name of the program, to incorporate in messages.

    The name is stored in argv[0]. */

    program_name = argv[0];

    do {

        next_option = getopt_long (argc, argv, short_options, long_options, NULL);

        switch (next_option)

       {

        case ‘h’: /* -h or --help */

        /* User has requested usage information. Print it to standard output, and exit with exit code zero (normal termination). */

            print_usage (stdout, 0);

        case ‘o’: /* -o or --output */

        /* This option takes an argument, the name of the output file. */

            output_filename = optarg;

            break;

        case ‘v’: /* -v or --verbose */

            verbose = 1;

            break;

        case ‘?’: /* The user specified an invalid option. */

        /* Print usage information to standard error, and exit with exit code one (indicating abnormal termination). */

            print_usage (stderr, 1);

        case -1: /* Done with options. */

            break;

        default: /* Something else: unexpected. */

            abort ();

        }

    } while (next_option != -1);

    /* Done with options. OPTIND points to first nonoption argument. For demonstration purposes, print them if the verbose option was specified. */

    if (verbose) {

        int i;

        for (i = optind; i < argc; ++i)

            printf (“Argument: %s/n”, argv[i]);

    }

    /* The main program goes here. */

    return 0;

}

% program > output_file.txt 2>&1

% program 2>&1 | filter

2<&1表示文件描述符2也即stderr将合并到文件描述符1也即stdout中。

欲重定向stdout和stderr到一个文件，2>&1必须跟在一个文件后面。

欲重定向stdout和stderr到一个管道，2>&1必须在一个管道前面。

% ls /

bin coda etc lib misc nfs proc sbin usr

boot dev home lost+found mnt opt root tmp var

% echo $?

0

% ls bogusfile

ls: bogusfile: No such file or directory

% echo $?

1

#include

/* The ENVIRON variable contains the environment. */

extern char** environ;

int main ()

{

    char** var;

    for (var = environ; *var != NULL; ++var)

    printf (“%s/n”, *var);

    return 0;

}

#include

#include

/* A handle for a temporary file created with write_temp_file. In this implementation, it’s just a file descriptor. */

typedef int temp_file_handle;

/* Writes LENGTH bytes from BUFFER into a temporary file. The temporary file is immediately unlinked. Returns a handle to the temporary file. */

temp_file_handle write_temp_file (char* buffer, size_t length)

{

    /* Create the filename and file. The XXXXXX will be replaced with characters that make the filename unique. */

    char temp_filename[] = “/tmp/temp_file.XXXXXX”;

    int fd = mkstemp (temp_filename);

    /* Unlink the file immediately, so that it will be removed when the file descriptor is closed. */

    unlink (temp_filename);

    /* Write the number of bytes to the file first. */

    write (fd, &length, sizeof (length));

    /* Now write the data itself. */

    write (fd, buffer, length);

    /* Use the file descriptor as the handle for the temporary file. */

    return fd;

}

/* Reads the contents of a temporary file TEMP_FILE created with write_temp_file. The return value is a newly allocated buffer of those contents, which the caller must deallocate with free. LENGTH is set to the size of the contents, in bytes. The temporary file is removed. */

char* read_temp_file (temp_file_handle temp_file, size_t* length)

{

    char* buffer;

    /* The TEMP_FILE handle is a file descriptor to the temporary file. */

    int fd = temp_file;

    /* Rewind to the beginning of the file. */

    lseek (fd, 0, SEEK_SET);

    /* Read the size of the data in the temporary file. */

    read (fd, length, sizeof (*length));

    /* Allocate a buffer and read the data. */

    buffer = (char*) malloc (*length);

    read (fd, buffer, *length);

    /* Close the file descriptor, which will cause the temporary file to go away. */

    close (fd);

    return buffer;

}

% ar cr libtest.a test1.o test2.o

% gcc -c -fPIC test1.c

% gcc -shared -fPIC -o libtest.so test1.o test2.o

% gcc -o app app.o -L. –ltest

% gcc -static -o app app.o -L. –ltest

Create test1.c

void f1()

{

printf("Test 1 fucntion 1");

}

gcc -c -fPIC test1.c

-rw-rw-r-- 1 liuchao liuchao 1124 Jul 31 19:51 test1.o

Create test2.c

void f2()

{

printf("Test 2 function 2");

}

gcc -c -fPIC test2.c

-rw-rw-r-- 1 liuchao liuchao 1124 Jul 31 19:52 test2.o

Create libstatictest.a

ar cr libstatictest.a test1.o test2.o

-rw-rw-r-- 1 liuchao liuchao 2508 Jul 31 19:53 libstatictest.a

Create libdynamictest.so

gcc -shared -fPIC -o libdynamictest.so test1.o test2.o

-rwxrwxr-x 1 liuchao liuchao 4573 Jul 31 19:54 libdynamictest.so

Create app.c

int main(int argc, char* argv[])

{

f2();

}

gcc -c app.c

-rw-rw-r-- 1 liuchao liuchao 772 Jul 31 19:55 app.o

Create staticapp

gcc -o staticapp app.o -L. –lstatictest

-rwxrwxr-x 1 liuchao liuchao 4861 Jul 31 19:56 staticapp

Create dynamicapp

gcc -o dynamicapp app.o -L. -ldynamictest

Run staticapp

./staticapp

Test 2 function 2

Run dynamicapp

./dynamicapp

./dynamicapp: error while loading shared libraries: libdynamictest.so: cannot open shared object file: No such file or directory

Ldd staticapp

ldd staticapp

linux-gate.so.1 => (0x0060d000)

libc.so.6 => /lib/libc.so.6 (0x007a3000)

/lib/ld-linux.so.2 (0x00786000)

Ldd dynamicapp

ldd dynamicapp

linux-gate.so.1 => (0x00861000)

libdynamictest.so => not found

libc.so.6 => /lib/libc.so.6 (0x00111000)

/lib/ld-linux.so.2 (0x00786000)

export LD_LIBRARY_PATH=.

export LD_LIBRARY_PATH=.

echo $LD_LIBRARY_PATH

.

./dynamicapp

Test 2 function 2

#include

#include

int main (int argc, char** argv)

{

TIFF* tiff;

tiff = TIFFOpen (argv[1], “r”);

TIFFClose (tiff);

return 0;

}

% ldd tifftest

libtiff.so.3 => /usr/lib/libtiff.so.3 (0x4001d000)

libc.so.6 => /lib/libc.so.6 (0x40060000)

libjpeg.so.62 => /usr/lib/libjpeg.so.62 (0x40155000)

libz.so.1 => /usr/lib/libz.so.1 (0x40174000)

/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)

% gcc -static -o tifftest tifftest.c -ltiff

/usr/bin/../lib/libtiff.a(tif_jpeg.o): In function ‘TIFFjpeg_error_exit’:

tif_jpeg.o(.text+0x2a): undefined reference to ‘jpeg_abort’

/usr/bin/../lib/libtiff.a(tif_jpeg.o): In function ‘TIFFjpeg_create_compress’:

tif_jpeg.o(.text+0x8d): undefined reference to ‘jpeg_std_error’

tif_jpeg.o(.text+0xcf): undefined reference to ‘jpeg_CreateCompress’

...

% gcc -static -o app app.o -lfoo -lbar –lfoo

例如程序app中的函数void a()在libfoo.a的A.o中实现，A.o中的函数void b()在libbar.a的B.o中实现，B.o中的函数void c()在libfoo.a的C.o中实现。则链接器的工作过程如下：

• 当扫描到-lfoo的时候，发现app的void a()没有定义，于是将其中的A.o提取出来，链接到app中。
• 当扫描到-lbar的时候，发现A.o中的函数void b()没有定义，于是将其中的B.o提取出来，链接到app中。
• 当扫描到-lfoo的时候，发现B.o的void c()函数没有定义，于是将其中的C.o提取出来，链接到app中。

void* handle = dlopen (“libtest.so”, RTLD_LAZY);

void (*test)() = dlsym (handle, “my_function”);

(*test)();

dlclose (handle);