Add shell scripting support

kernel/exec.c

@@ -39,6 +39,28 @@ exec(char *path, char **argv)
   }
   ilock(ip);
 
+  // Check for #! at the beginning
+  // Shell scripts look like this at the start:
+  // #!/sh argument (argument not implemented)
+  char shebang[2];
+  readi(ip, 0, (uint64)&shebang, 0, sizeof(shebang));
+  if (shebang[0] == '#' && shebang[1] == '!') {
+    char interpreter[MAXPATH];
+    int read_sz = readi(
+      ip, 0, (uint64)&interpreter, sizeof(shebang), sizeof(interpreter));
+    for (int i = 0; i < MAXPATH && i < read_sz; ++i) {
+      if (interpreter[i] == '\n' || interpreter[i] == ' ') {
+        interpreter[i] = '\0';
+        break;
+      }
+    }
+
+    char *new_argv[] = { interpreter, argv[0], 0 };
+    iunlockput(ip);
+    end_op();
+    return exec(interpreter, new_argv);
+  }
+
   // Check ELF header
   if(readi(ip, 0, (uint64)&elf, 0, sizeof(elf)) != sizeof(elf))
     goto bad;

tests/shell-scripting/test.sh

@@ -0,0 +1,10 @@
+#!/sh
+# Please add this to Makefile to test
+
+echo Testing shell script functionality
+echo 
+echo Welcome to my script
+echo My script is amazing
+echo Look at these files
+ls /
+echo Byte now

user/sh.c

@@ -132,18 +132,19 @@ runcmd(struct cmd *cmd)
 }
 
 int
-getcmd(char *buf, int nbuf)
+getcmd(char *buf, int nbuf, int fd)
 {
-  write(2, "$ ", 2);
+  if (fd == 0)
+    write(2, "$ ", 2); // only print prompt if interactive (no script)
   memset(buf, 0, nbuf);
-  gets(buf, nbuf);
+  fgets(fd, buf, nbuf);
   if(buf[0] == 0) // EOF
     return -1;
   return 0;
 }
 
 int
-main(void)
+main(int argc, char *argv[])
 {
   static char buf[100];
   int fd;
@@ -156,8 +157,16 @@ main(void)
     }
   }
 
+  fd = 0;
+  if (argc > 1) {
+    fd = open(argv[1], O_RDONLY);
+  }
+
   // Read and run input commands.
-  while(getcmd(buf, sizeof(buf)) >= 0){
+  while(getcmd(buf, sizeof(buf), fd) >= 0){
+    if (buf[0] == '#') {
+      continue;
+    }
     if(buf[0] == 'c' && buf[1] == 'd' && buf[2] == ' '){
       // Chdir must be called by the parent, not the child.
       buf[strlen(buf)-1] = 0;  // chop \n