ifaddr initial import

.gitignore

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+/build/
+

README.adoc

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+= Read me
+
+This command outputs the ipv4 address for the interface given by name in argument.

src/Makefile

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+DESTDIR=../build
+
+$(DESTDIR)/ifaddr: main.c getifaddr.c
+	mkdir -p $(DESTDIR)
+	gcc  $^ -o $(DESTDIR)/ifaddr
+
+dist-clean:
+	rm -f ifaddr $(DESTDIR)/ifaddr
+

src/getifaddr.c

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+#define _GNU_SOURCE     /* To get defns of NI_MAXSERV and NI_MAXHOST */
+#include <ifaddrs.h>
+#include <arpa/inet.h>
+#include <sys/socket.h>
+#include <netdb.h>
+#include <ifaddrs.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <linux/if_link.h>
+#include <string.h>
+
+char * get_if_addr(char *ifname)
+{
+
+  struct ifaddrs * list, * plist;
+  int family, s;
+
+	char host[NI_MAXHOST];
+  char *result;
+  if (getifaddrs (&list)==-1)
+  {
+    fprintf(stderr, "no info");
+    return NULL;
+  }
+  plist = list;
+  while (plist!=NULL)
+  {
+    if (strcmp(plist->ifa_name,ifname)==0) 
+		{
+      family = plist->ifa_addr->sa_family;
+      if (family == AF_INET || family == AF_INET6) {
+                   s = getnameinfo(plist->ifa_addr,
+                           (family == AF_INET) ? sizeof(struct sockaddr_in) :
+                                                 sizeof(struct sockaddr_in6),
+                           host, NI_MAXHOST,
+                           NULL, 0, NI_NUMERICHOST);
+                   if (s != 0) {
+                       fprintf(stderr, "getnameinfo() failed: %s\n", gai_strerror(s));
+                       exit(EXIT_FAILURE);
+                   }
+                   result = malloc(strlen(host)+1);
+                   strcpy(result,host);
+                   freeifaddrs (list);
+                   return result;
+               }
+    }
+    plist = plist->ifa_next;
+  }
+  freeifaddrs (list);
+  return NULL;
+
+}

src/main.c

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+#include <stdio.h>
+#include<stdlib.h>
+
+char * get_if_addr(char *ifname);
+
+int main(int argc, char ** argv)
+{
+
+  if (argc<2) {
+    fprintf(stderr, "usage: %s <ifname>\nOù `ifname` est le nom de l'interface, par exemple, `eth0`.", argv[0]);
+    
+    return 2;
+  }
+
+    char * addr = (char*) get_if_addr(argv[1]);
+    if (addr==NULL) {
+      printf("no addr found!\n");
+      return 1;
+    }
+    printf(addr);
+
+    free(addr);
+    return 0;
+}