prenv.c

/*
 * program to print environment variables
 * invocation:
 *	prenv		print argument list
 *	prenv arg1 ...	print value of argument(s)
 * exit code: number of environment variables not found
 * author: Matt Bishop, bishop@cs.ucdavis.edu, 9/16/96
 */
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

int main(int argc, char *argv[], char *envp[])
{
	register int i;			/* counter in for loops */
	register int narg;		/* number of current argument */
	register int len;		/* length of current argument */
	register int found;		/* 1 if env. variable found */
	register int exstat = 0;	/* exit status code */

	/*
	 * no arguments; just print the environment
	 * variables and their values
	 */
	if (argc == 1){
		/* just loop and print */
		for(i = 0; envp[i] != NULL; i++)
			printf("%s\n", envp[i]);
		/* all done! */
		return(EXIT_SUCCESS);
	}

	/*
	 * arguments given; just print the values
	 * associated with these named variables
	 */
	for(narg = 1; argv[narg] != NULL; narg++){
		/* just an optimization ... */
		len = strlen(argv[narg]);
		/* assume no such variable */
		found = 0;
		/*
		 * now look for the variable
		 */
		for(i = 0; envp[i] != NULL; i++)
			/* see if this one is it*/
			if (strncmp(envp[i], argv[narg], len) == 0){
				/* name= means value follows = */
				if (envp[i][len] == '='){
					printf("%s\n", envp[i] + len + 1);
					found++;
				}
				/* name means value is empty */
				/* anything else, it doesn't match */
				else if (!envp[i][len]){
					putchar('\n');
					found++;
				}
			}
		/*
		 * did we find it?
		 */
		if (!found){
			/* nope -- print error message */
			fprintf(stderr, "%s: no such variable\n", argv[narg]);
			/* one more unknown environment variable */
			exstat++;
		}

	}

	/*
	 * return number of unknown environment variables
	 */
	return(exstat);
}

Matt Bishop Office: 2209 Watershed Sciences Phone: +1 (530) 752-8060 Email: mabishop@ucdavis.edu

ECS 36A, Programming & Problem Solving Version of April 2, 2024 at 12:13PM

You can get the raw source code here.