exec and get pid

exec is used for start another program in the c code of linux

1.execl

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1. int execl(const char*path,const char* arg,...)  

the last parameter must end up with NULL.

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1. #include <stdio.h>  
2. #include <unistd.h>  
3. int main()  
4. {  
5.     execl("/home/cascais/code/hello","hello","3",NULL);  
6.     return 0;  
7. }  

the path can be absolutely path or relative path like "./hello"

 

2.execlp

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1. <pre name="code" class="cpp">int execl(const char*path,const char* arg,...)  

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1. #include <stdio.h>  
2. #include <unistd.h>  
3. int main()  
4. {  
5.     execlp("pwd","pwd",NULL);  
6.     return 0;  
7. }  

it won't work with execl. execl need the full path "/bin/pwd"

 

3.execv

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1. int execv(const char* path,const char* argv[])  

use string array instead of string list.

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1. #include <stdio.h>  
2. #include <unistd.h>  
3. int main()  
4. {  
5.     char* argv[] = {"ls" , "-al", NULL};  
6.     execv("/bin/ls", argv);  
7.     return 0;  
8. }  

must has NULL

4.execv

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1. int execve(const char* path,const char* argv[], char * const evnp[]);  

 

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1. #include <stdio.h>  
2. #include <unistd.h>  
3. int main()  
4. {  
5.     char* argv[] = {"echo" , "$PATH", NULL};  
6.     char * evnp[]={"PATH=/bin",0};  
7.     execve("/bin/echo", argv, evnp);  
8.     return 0;  
9. }  

it turns to be "$PATH" , not "/bin"

I havn't found what "evnp" is for.

 

5. ececvp

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1. int execv(const char* path,const char* argv[])  

like ececlp

but use argv instead of sting list.

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1. <pre name="code" class="cpp">#include <stdio.h>  
2. #include <unistd.h>  
3. int main()  
4. {  
5.     char* argv[] = {"ls" , "-al", NULL};  
6.     execvp("ls", argv);  
7.     return 0;  
8. }  

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1. </pre><pre name="code" class="cpp" style="background-color: rgb(255, 255, 255); ">  

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1. </pre><pre name="code" class="cpp" style="background-color: rgb(255, 255, 255); "><pre>  

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1. #include <unistd.h>  
2. #include <stdio.h>  
3. #include <sys/syscall.h>  
4. #include <unistd.h>  
5.   
6. #define gettid() ((pid_t) syscall(SYS_gettid))  
7. int main()  
8. {  
9.     printf("start pid=%d,tid=%d\n", getpid(),gettid());  
10.       
11. } 
    

转载于:https://www.cnblogs.com/elfylin/archive/2012/04/02/2430240.html