Creating a Command Line Interface in C

Embedded system development often requires command line functionality, such as the uboot command line. The command line can enhance the flexibility of program execution, facilitate debugging, and significantly improve our development efficiency. This article provides a simple example to teach you how to implement a basic command line module that can be easily ported to your own C projects.

1. Design Philosophy
2. Implementation
1. Structure: The command-related information supported by the module is maintained using the struct _cmdnum.
typedef void (* CMDFUNC)(char [][256],int argc);
typedef struct _cmdnum{
    char *cmd;
    int index;
    int paramcount;
    CMDFUNC callback;
    char *info;
}CMDNUM,*PCMDNUM;

Members
Meaning
char *cmd
Command name
int index
Command index
int paramcount
Number of command parameters
CMDFUNC callback
Callback function corresponding to the command

2. Supported Commands: In this example, four commands are added:

Function
Number of Parameters
Callback Function
help
Display all command information
0
showhelp()
exit
Exit the current process
0
quit()
test
Print all parameter information for testing
3
test()
send
Convert the input hexadecimal string to a hexadecimal integer and store it in an array
MAX_PARAM_NUM
send()

Defined as follows:
CMDNUM cmdlist[] =
{
    {"help",1,0,showhelp},
    {"exit",2,0,quit},
    {"test",3,3,test},
    {"send",4,MAX_PARAM_NUM,send},
};

3. Related Functions
1. getline()#include <stdio.h>
ssize_t getline(char **lineptr, size_t *n, FILE *stream);
Reads a line of data from the file stream stream, saving the result to *lineptr, including the null character and newline character at the end.

2. parsecmd()void parsecmd(char *s)
Parses the command line content, mainly implemented through the functions stripcmd/getcmdindex.

• stripcmd

int stripcmd(char *s,char cmds[][256])

Using the library function strtok, it separates the parameters in the command line s by spaces, extracts the parameters, and stores them in the two-dimensional array **char cmds[256]**.

• getcmdindex

int getcmdindex(char *name)

By the command namename, it traverses the arraycmdlist[] and obtains the array index index.

4. Core Code

CMDNUM cmdlist[] =
{
    {"help",1,0,showhelp,"show all cmd info"},
    {"exit",2,0,quit,"quit application"},
    {"test",3,3,test,"[param...]print params"},
    {"send",3,MAX_PARAM_NUM,senddata,"[xx...]converts data from string to hex and store to buf"},
};

void parsecmd(char *s)
{
char cmd[MAX_PARAM_NUM][256];
int argc = 0;
int index = -1;

argc = stripcmd(s,cmd);

//printf("argc=%d\n",argc);
index=getcmdindex(cmd[0]);
if(index == -1)
{
if(argc>0)
{
   cprintf(RED,"\tNo such command \n");
}
return;
}
elseif(argc>0)
{
  cmdlist[index].callback(cmd,argc);
}
}

UINT8 hex2char(UINT8 ch)
{
if ((ch >= '0') && (ch <= '9')) {return ch - '0';}
if ((ch >= 'a') && (ch <= 'f')) {return ch - 'a' + 10;}
if ((ch >= 'A') && (ch <= 'F')) {return ch - 'A' + 10;}
return (UINT8)0xff;
}

UCHAR stringToByte(char* str)
{
 UCHAR bytes = 0;

if(strlen(str)==1)
{
  bytes= 0 << 4 | hex2char(str[0]);
}else
{
  bytes= hex2char(str[0]) << 4 | hex2char(str[1]);
}

return bytes;
}
//7e 01 02 01 00 07 07 01 00 00 00 c6 51 2a 7e

void senddata(char argv[][256],int argc)
{
int i = 0;
int len = 0;
UCHAR buf[256] = {0};

if(argc < 2)
{
return;
}
for(i=1;i<argc;i++)
{
   buf[i-1] = stringToByte(argv[i]);
}
cprintf(GREEN,"\n  buf:");
for(i=0;i<argc-1;i++)
{
cprintf(GREEN,"%02x ",buf[i]);
}
putchar('\n');
}
void test(char argv[][256],int argc)
{
int i = 0;

for(i=0;i<argc;i++)
{
cprintf(YEL,"\targv[%d]:%s\n",i,argv[i]);
}

return;
}
void showsysinfo(void)
{
cprintf(D_GREEN_H,"---------------yikoulinux cmdline demo-----------\n");
}
void quit(char cmd[][256],int argc)
{
    cprintf(RED_H,"exit to system \n");
    exit(0);
}

void showhelp(char cmd[][256],int argc)
{
int i = 0;

for(i=0;i<sizeof(cmdlist)/sizeof(CMDNUM);i++)
{
cprintf(GREEN_H,"\t%s",cmdlist[i].cmd);
cprintf(YEL_H,"\t%s\n",cmdlist[i].info);
}
return;
}

int main(int argc, char* argv[])
{
    char *line;
    int ret = 0;
size_t len_line = 0;

    showsysinfo();
    
while(1)
{
  fflush(stdin);
  cprintf(D_GREEN_H,DEV_NAME"# ");

  ret = getline(&line, &len_line, stdin);
if(ret == -1)
  {
   break;
}
  parsecmd(line);
free(line);
  line = NULL;
}
   
    return 0;
}

3. Testing

1. help

2. test

3. send

4. exit

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