linux c -- 环境变量和参数

#include <stdlib.h>#include <stdio.h>#include <string.h>int main (int argc , char *argv[]){char *var,*value;if( argc == 1 || argc == 3 ){fprintf(stderr , "usage:environ var [value]\n");exit(1);}var = argv[1];value = getenv(var);if(value)printf( "Variable %s has value %s \n" , var , value );elseprintf( "Variable %s has no value \n" , var );if(argc == 3){char * string;value = argv[2];string = malloc( strlen(var) + strlen(value) + 2 );if( string == NULL ){fprintf(stderr , "out of memory \n");exit(1);}strcpy(string , var );strcat( string , "=" );strcat( string , value );printf( "Calling putenv with : %s\n" , string );if(putenv(string) != 0 ){fprintf(stderr , "putenv faild \n");free(string);exit(1);}value = getenv(var);if(value)printf("New value of %s is %s\n" , var , value );elseprintf("New value of %s is null ?? \n" , var );}exit(0);}