add getenv

Signed-off-by: Mattias Andrée <maandree@member.fsf.org>

1 files changed, 73 insertions, 0 deletions

diff --git a/src/stdlib/getenv.c b/src/stdlib/getenv.c
new file mode 100644
index 0000000..e0302f1
--- /dev/null
+++ b/src/stdlib/getenv.c
@@ -0,0 +1,73 @@
+/**
+ * slibc — Yet another C library
+ * Copyright © 2015  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+
+
+
+/**
+ * The process's environment variables.
+ */
+extern char** environ;
+
+
+
+/**
+ * This function returns the value assoicated with a
+ * specified environment variable.
+ * 
+ * Portable program must not check `errno`. No errors
+ * are defined by POSIX.
+ * 
+ * @etymology  (Get) the value of an (env)ironment variable!
+ * 
+ * @param   name  The name of the sought environment variable.
+ *                Must not be `NULL`.
+ * @return        The value of the environment variable.
+ *                `NULL` on error, or if not found. This
+ *                pointer is subpointer, and must not be
+ *                modified except for in-place changes.
+ * 
+ * @throws  0       No such environment variable found.
+ *                  This is a slibc extensions.
+ * @throws  EINVAL  `name` is `NULL` (must not be the case), empty,
+ *                  or contains a '='. This is a slibc extensions.
+ * 
+ * @since  Always.
+ */
+char* getenv(const char* name)
+{
+  size_t i, n;
+  
+  if (!name || !*name || strchr(name, '='))
+    return errno = EINVAL, NULL;
+  
+  errno = 0;
+  if (environ == NULL)
+    return NULL;
+  
+  n = strlen(name);
+  for (i = 0; environ[i] != NULL; i++)
+    if (!strncmp(name, environ[i], n))
+      if (environ[i][n] == '=')
+	return environ[i] + n + 1;
+  
+  return NULL;
+}
+