[PATCH v2] Add initial version of xargs(1)

---
 Makefile |   1 +
 xargs.c  | 238 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 239 insertions(+)
 create mode 100644 xargs.c
diff --git a/Makefile b/Makefile
index 2a72a1c..81dfaf6 100644
--- a/Makefile
+++ b/Makefile
_AT_@ -93,6 +93,7 @@ SRC = \
 	stat.c     \
 	wc.c       \
 	who.c      \
+	xargs.c    \
 	yes.c
 
 OBJ = $(SRC:.c=.o) $(LIB)
diff --git a/xargs.c b/xargs.c
new file mode 100644
index 0000000..4dd858d
--- /dev/null
+++ b/xargs.c
_AT_@ -0,0 +1,238 @@
+/* See LICENSE file for copyright and license details. */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "text.h"
+#include "util.h"
+
+static int inputc(void);
+static void deinputc(int);
+static void fillbuf(int);
+static void eatspace(void);
+static char *poparg(void);
+static int parsesquote(void);
+static int parsedquote(void);
+static char *poparg(void);
+static void pusharg(char *);
+static int runcmd(void);
+
+static void
+usage(void)
+{
+	eprintf("usage: %s [-r] [cmd [arg...]]", argv0);
+}
+
+static char **cmd;
+static char *argb;
+static size_t argbsz = 1;
+static size_t argbpos;
+static int rflag = 0;
+
+int
+main(int argc, char *argv[])
+{
+	char *arg;
+	int i = 0;
+
+	ARGBEGIN {
+	case 'r':
+		rflag = 1;
+		break;
+	default:
+		usage();
+	} ARGEND;
+
+	cmd = malloc(sysconf(_SC_ARG_MAX) * sizeof(*cmd));
+	if (!cmd)
+		eprintf("malloc:");
+
+	argb = malloc(argbsz);
+	if (!argb)
+		eprintf("malloc:");
+
+	do {
+		if (argc > 0)
+			for (i = 0; i < argc; i++)
+				cmd[i] = strdup(argv[i]);
+		else
+			cmd[i++] = strdup("/bin/echo");
+		while ((arg = poparg())) {
+			if (i < sysconf(_SC_ARG_MAX) - 1) {
+				cmd[i++] = strdup(arg);
+			} else {
+				pusharg(arg);
+				break;
+			}
+		}
+		cmd[i] = NULL;
+		if (i == 1 && rflag == 1); else runcmd();
+		for (; i >= 0; i--)
+			free(cmd[i]);
+	} while (arg);
+
+	free(argb);
+	free(cmd);
+	return 0;
+}
+
+static int
+inputc(void)
+{
+	int ch;
+
+	ch = getc(stdin);
+	if (ch == EOF && ferror(stdin))
+		eprintf("stdin: read error:");
+	return ch;
+}
+
+static void
+deinputc(int ch)
+{
+	ungetc(ch, stdin);
+}
+
+static void
+fillbuf(int ch)
+{
+	if (argbpos >= argbsz) {
+		argbsz *= 2;
+		argb = realloc(argb, argbsz);
+		if (!argb)
+			eprintf("realloc:");
+	}
+	argb[argbpos] = ch;
+}
+
+static void
+eatspace(void)
+{
+	int ch;
+
+	while ((ch = inputc()) != EOF) {
+		switch (ch) {
+		case ' ': case '\t': case '\n':
+			break;
+		default:
+			deinputc(ch);
+			return;
+		}
+	}
+}
+
+static int
+parsesquote(void)
+{
+	int ch;
+
+	while ((ch = inputc()) != EOF) {
+		switch (ch) {
+		case '\'':
+			fillbuf('\0');
+			return 0;
+		default:
+			if (ch != '\n') {
+				fillbuf(ch);
+				argbpos++;
+			}
+			break;
+		}
+	}
+	return -1;
+}
+
+static int
+parsedquote(void)
+{
+	int ch;
+
+	while ((ch = inputc()) != EOF) {
+		switch (ch) {
+		case '\"':
+			fillbuf('\0');
+			return 0;
+		default:
+			if (ch != '\n') {
+				fillbuf(ch);
+				argbpos++;
+			}
+			break;
+		}
+	}
+	return -1;
+}
+
+static char *
+poparg(void)
+{
+	int ch;
+	int escape = 0;
+
+	argbpos = 0;
+	eatspace();
+	while ((ch = inputc()) != EOF) {
+		switch (ch) {
+		case ' ': case '\t': case '\n':
+			if (escape == 1) {
+				escape = !escape;
+				if (ch != '\n') {
+					fillbuf(ch);
+					argbpos++;
+					break;
+				}
+			}
+			fillbuf('\0');
+			deinputc(ch);
+			return argb;
+		case '\'':
+			if (parsesquote() == -1)
+				enprintf(EXIT_FAILURE,
+					 "unterminated single quote\n");
+			break;
+		case '\"':
+			if (parsedquote() == -1)
+				enprintf(EXIT_FAILURE,
+					 "unterminated double quote\n");
+			break;
+		case '\\':
+			escape = !escape;
+			break;
+		default:
+			fillbuf(ch);
+			argbpos++;
+			break;
+		}
+	}
+	if (argbpos > 0) {
+		fillbuf('\0');
+		return argb;
+	}
+	return NULL;
+}
+
+static void
+pusharg(char *arg)
+{
+	char *p;
+
+	for (p = &arg[strlen(arg) - 1]; p >= arg; p--)
+		deinputc(*p);
+}
+
+static int
+runcmd(void)
+{
+	pid_t pid;
+
+	pid = fork();
+	if (pid < 0)
+		eprintf("fork:");
+	if (pid == 0) {
+		execvp(*cmd, cmd);
+		eprintf("execvp %s:", *cmd);
+	}
+	wait(NULL);
+	return 0;
+}
-- 
1.8.4.5
--envbJBWh7q8WU6mo--