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Linux下C语言开发的命令行工具，大都使用getopt来做命令行参数的解析。（除非特别简单的场景，直接读取argv的值也可以）
两个概念：
-开始的命令行参数叫做short option；--开始的命令行参数叫做long option；都是option，可选的。
因此，具体某个命令行参数如果没有配置，但又是必须的，需要程序员自己处理。
getopt只支持short option，如果需要long option，需要使用getopt_long或getopt_long_only，具体参考man 3 getopt。
相对来说，Python的argparse模块支持的功能就太丰富了，使用也更简单。
下面是一个简单的测试代码：
$ cat test_getopt.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc, char **argv) {
for (int i=0; i<argc; ++i)
printf("%s\n", argv[i]);
int opt;
while ((opt=getopt(argc,argv,"a:b:")) != -1) {
switch(opt) {
case 'a':
printf("short option -a: %d\n", atoi(optarg));
break;
case 'b':
printf("short option -b: %s\n", optarg);
break;
default:
printf("option error\n");
break;
}
}
return 0;
}
这段代码先将所有命令行参数打印一遍，然后再用getopt去获取两个short option。optarg是用来获取具体参数值的全局变量。"a:b:"表示a和b都是short option，并且:表明了它俩后面可以带参数值。
各位同学可以用这段代码测试并感觉一些getopt的功能，-a和-b都是short option。下面是我自己的一点测试结果：
$ gcc -Wall -Wextra test_getopt.c -o test_getopt
$ ./test_getopt # no argument
./test_getopt
$ ./test_getopt -a 1 # only -a
./test_getopt
-a
1
short option -a: 1
$ ./test_getopt -a 1 -b gg # both -a and -b
./test_getopt
-a
1
-b
gg
short option -a: 1
short option -b: gg
$ ./test_getopt -a1 -bgg # both -a and -b, no space between option and argument
./test_getopt
-a1
-bgg
short option -a: 1
short option -b: gg
$ ./test_getopt -a1 -bgg x y z # positional argument
./test_getopt
-a1
-bgg
x
y
z
short option -a: 1
short option -b: gg
$ ./test_getopt x -a1 y -bgg z # positional argument
./test_getopt
x
-a1
y
-bgg
z
short option -a: 1
short option -b: gg
$ ./test_getopt -a1 -- -bgg ## special argument --
./test_getopt
-a1
--
-bgg
short option -a: 1
现在来说一些getopt的内部原理：getopt会对argv进行排序，将short option排在前面，它自己先处理，这必然就会导致其它positional argument（non-option）全部被移动到末尾，不过这个细节上面的测试代码还看不出来，下面还会有更丰富的测试代码来说明。--是命令行的特殊参数，当getopt解析到这个特殊参数的时候就停止继续，后面的所有参数，都被当作non option的positional参数。上例中最后一次测试，-bgg就被当成了非short option。
下面再来一段测试代码：
$ cat test_getopt.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(void) {
int opt;
int argc;
char **argv;
// ---- case 1 ----
printf("\n# options without argument:\n");
optind = 0;
char *argv1[] = {"","-a","-b"};
argc = sizeof(argv1) / sizeof(char*);
argv = argv1;
while ((opt=getopt(argc,argv,"ab")) != -1) {
switch(opt) {
case 'a':
printf("short option -a is received\n");
break;
case 'b':
printf("short option -b is received\n");
break;
default:
printf("option error\n");
break;
}
}
printf("at last optind = %d\n", optind);
// ---- case 2 ----
printf("\n# options with argument:\n");
optind = 0;
char *argv2[] = {"","-a123","-d","-bcde","-c","j789"};
argc = sizeof(argv2) / sizeof(char*);
argv = argv2;
while ((opt=getopt(argc,argv,"a:b:c:d:")) != -1) {
switch(opt) {
case 'a':
printf("short option -a: %d\n", atoi(optarg));
break;
case 'b':
printf("short option -b: %s\n", optarg);
break;
case 'c':
printf("short option -c: %s\n", optarg);
break;
case 'd':
printf("short option -d: %s\n", optarg);
break;
default:
printf("option error\n");
break;
}
}
printf("at last optind = %d\n", optind);
// ---- case 3 ----
printf("\n# options and positional arguments:\n");
optind = 0;
char *argv3[] = {"","p1","-a123","p2","-bcde","p3","-d","p4"};
argc = sizeof(argv3) / sizeof(char*);
argv = argv3;
while ((opt=getopt(argc,argv,"a:b:d")) != -1) {
switch(opt) {
case 'a':
printf("short option -a: %d\n", atoi(optarg));
break;
case 'b':
printf("short option -b: %s\n", optarg);
break;
case 'd':
printf("short option -d is received\n");
break;
default:
printf("option error\n");
break;
}
}
printf("now optind = %d\n", optind);
for (int i=optind; i<argc; ++i)
printf("positional argument %d: %s\n", i-optind, argv[i]);
// ---- case 4 ----
printf("\n# special argument -- :\n");
optind = 0;
char *argv4[] = {"","p1","-a123","p2","-bcde","--","p3","-d","p4"};
argc = sizeof(argv4) / sizeof(char*);
argv = argv4;
while ((opt=getopt(argc,argv,"a:b:d")) != -1) {
switch(opt) {
case 'a':
printf("short option -a: %d\n", atoi(optarg));
break;
case 'b':
printf("short option -b: %s\n", optarg);
break;
case 'd':
printf("short option -d is received\n");
break;
default:
printf("option error\n");
break;
}
}
printf("now optind = %d\n", optind);
for (int i=optind; i<argc; ++i)
printf("positional argument %d: %s\n", i-optind, argv[i]);
// ---- case 5 ----
printf("\n# GNU extension + (stop at the first positional argument):\n");
optind = 0;
char *argv5[] = {"","-a123","p1","-bcde","-d","p2"};
argc = sizeof(argv5) / sizeof(char*);
argv = argv5;
while ((opt=getopt(argc,argv,"+a:b:d")) != -1) {
switch(opt) {
case 'a':
printf("short option -a: %d\n", atoi(optarg));
break;
case 'b':
printf("short option -b: %s\n", optarg);
break;
case 'd':
printf("short option -d is received\n");
break;
default:
printf("option error\n");
break;
}
}
printf("now optind = %d\n", optind);
for (int i=optind; i<argc; ++i)
printf("positional argument %d: %s\n", i-optind, argv[i]);
return 0;
}
以上测试代码，模拟了好几种不同的命令行参数场景。optind也是一个可以使用的全局变量，它指向重排序后的参数的index。
下面是这段测试代码的运行效果：
$ gcc -Wall -Wextra test_getopt.c -o test_getopt
$ ./test_getopt
# options without argument:
short option -a is received
short option -b is received
at last optind = 3
# options with argument:
short option -a: 123
short option -d: -bcde
short option -c: j789
at last optind = 6
# options and positional arguments:
short option -a: 123
short option -b: cde
short option -d is received
now optind = 4
positional argument 0: p1
positional argument 1: p2
positional argument 2: p3
positional argument 3: p4
# special argument -- :
short option -a: 123
short option -b: cde
now optind = 4
positional argument 0: p1
positional argument 1: p2
positional argument 2: p3
positional argument 3: -d
positional argument 4: p4
# GNU extension + (stop at the first positional argument):
short option -a: 123
now optind = 2
positional argument 0: p1
positional argument 1: -bcde
positional argument 2: -d
positional argument 3: p2
本文链接：https://cs.pynote.net/sf/linux/prog/202208291/
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