Lab util: xargs

Makefile

@@ -152,6 +152,7 @@ UPROGS=\
 	$U/_usertests\
 	$U/_grind\
 	$U/_wc\
+	$U/_xargs\
 	$U/_zombie\
 
 

user/xargs.c

@@ -0,0 +1,81 @@
+#include "kernel/param.h"
+#include "kernel/types.h"
+#include "user/user.h"
+
+int
+fmtpargs(char **pargs, char *buf, int n)
+{
+  int t = 0;
+  char *h = buf + 1, *p = buf + 1;
+  for (int i = 1; i < n; ++i) {
+    if (buf[i] == '\\' || buf[i] == '\"') {
+      pargs[t] = malloc(p - h);
+      memcpy(pargs[t++], h, p++ - h);
+      h = ++p;
+      ++i;
+    } else {
+      ++p;
+    }
+  }
+  return t;
+}
+
+void
+fmtsargs(char **sargs, int at, char *buf, int n)
+{
+  char *h = buf, *p = buf;
+  for (int i = 0; i <= n; ++i) {
+    if ((buf[i] == ' ' && (p - h)) || buf[i] == '\n') {
+      sargs[at] = malloc(p - h);
+      memcpy(sargs[at++], h, p - h);
+      h = ++p;
+    } else if (buf[i] == ' ') {
+      h = ++p;
+    } else {
+      ++p;
+    }
+  }
+}
+
+int
+main(int argc, char *argv[])
+{
+  char buf[512];
+  int n;
+
+  if ((n = read(0, buf, sizeof buf)) < 0) {
+    fprintf(2, "xargc: failed to read buf\n");
+    exit(1);
+  }
+
+  char *args[MAXARG + 1];
+  int at = 0;
+
+  if (!strcmp(argv[1], "-n")) {  // xargs -n 1 ...
+    for (int i = 3; i < argc; ++i) {
+      args[at] = malloc(sizeof argv[i]);
+      memcpy(args[at++], argv[i], sizeof argv[i]);
+    }
+    args[at] = malloc(24);  // assume max length 24
+    char *pargs[MAXARG];
+    int t = fmtpargs(pargs, buf, n);  // pargs[0...t]
+    for (int i = 0; i < t; ++i) {
+      memcpy(args[at], pargs[i], sizeof pargs[i]);
+      if (fork() == 0) {
+        exec(args[0], args);
+        exit(0);
+      } else {
+        wait(0);
+      }
+    }
+  } else {
+    for (int i = 1; i < argc; ++i) {
+      args[at] = malloc(sizeof argv[i]);
+      memcpy(args[at++], argv[i], sizeof argv[i]);
+    }
+    fmtsargs(args, at, buf, n);
+    exec(args[0], args);
+  }
+
+  exit(0);
+}