Linux C Programming (4)----Operating environment variables, program pass parameters getopt Getopt_long operation, acquisition time

View environment variables with command pass parameters

/*************************************************************************> File name:env.c> Author: > Mail: > Created time:tue 10:42:21 PM PST ****************************************************************   /#include <stdio.h> #include <stdlib.h>int main (int argc,char**argv) {char*p,*str; if (argc==1| |    argc>3) {printf ("Parameter Num is wrong!\n"); } else if (argc==2) {if ((P=getenv (argv[1))) {printf ("environment variable%s =%s\n", argv[        1],P);       }} else if (argc==3) {p= (char*) malloc (strlen (argv[1]) +strlen (argv[2]) +2);       strcpy (p,argv[1]);       Strcat (p, "=");        strcat (p,argv[2]);        if (Putenv (p) ==0) {printf ("Put env successful\n");          } if (Str=getenv (argv[1])) {printf ("Put Env%s:%s\n", argv[1],str);            }else {printf ("Get Env error!\n"); }//can not free on the front of This position free (p); } exit (0);}

View Global Environment variables

/*************************************************************************> File name:showenv.c> Author: > Mail: > Created time:tue 11:17:39 PM PST ************************************************************ /#include <stdio.h> #include <stdlib.h>extern  char * * environ; int main (int argc,char** argv) {    char **penv=environ;    while (*penv)    {        printf ("%s\n", *penv);        penv++;    }    Exit (0);}

Time operation

/*************************************************************************> File name:time.c> Author: > Mail: > Created time:wed 12:11:00 AM PST **************************************************************** /#include <stdio.h> #include <time.h>int main (int argc,char**argv) {   char timebuf[256];   time_t Tmt=time ((time_t*) NULL);   printf ("Unformat Time:%d\n", TMT);   printf ("Format time:%s\n", CTime (LocalTime (&tmt)));    Strftime (timebuf,256, "%m:%d", LocalTime (&tmt));   printf ("Format time:%s\n", timebuf);    Exit (0);}

Get login uid GID user

/*************************************************************************> File name:uid.c> Author: > Mail: > Created time:wed 12:51:53 AM PST **************************************************************** /#include <stdio.h> #include <unistd.h> #include <sys/types.h>int main () {  printf ("UID: %d\n ", Getuid ());  printf ("gid:%d\n", Getgid ());   printf ("currentlogined:%s\n", GetLogin ());  printf ("gethostid:%d\n", Gethostid ()); exit (0);}

Pass a simple program parameter

/************ > File name:option.c> Author: > Mail: > Created time:tue 06:30:00 PM PST ************************************************************************/   #include <stdio.h> #include <unistd.h>int main (int argc,char**argv) {int opt; while ((Opt=getopt (ARGC,ARGV, ": if:x")!=-1) {switch (opt) {case '? ': printf ("Unknow optio             n:%c \ n ", optopt);          Break             Case ': ': printf ("Option:%c Need Value\n", optopt);          Break             Case ' F ': printf ("File is%s \ n", Optarg);          Break             Case ' I ': Case ' x ': printf ("Option:%c\n", opt);       break;    }} for (; optind<argc;optind++) {printf ("arguments:%s \ n", Argv[optind]); } exit (0);} 

more complete Transfer parameters

/*************************************************************************> File name:option2.c> Author: > Mail: > Created time:tue 09:16:58 PM PST ************************************************************ /#include <stdio.h> #include <unistd.h> #include <getopt.h> #define _gnu_source int Main (    int argc,char**argv) {int opt;   struct option optlist[]={{"Add", 0,null, ' a '}, {"File", 1,null, ' f '}, {0,0,0,0}};            while ((Opt=getopt_long (ARGC,ARGV, ": AF:XCV", Optlist,null))!=-1) {switch (opt) {case ' a ':              Case ' x ': Case ' C ': Case ' V ': printf ("option:%c\n", opt);            Break              Case ': ': printf ("Option has value!\n");            Break              Case ' F ': printf ("File is%s\n", optarg);            break;              Case '? ': printf ("Option is unknow!\n");        break;    }    }    for (; optind<argc;optind++) {printf ("remained Parameter:%s\n", Argv[optind]); } exit (0);}

Linux C Programming (4)----Operating environment variables, program pass parameters getopt Getopt_long operation, acquisition time