pscat(1)

src/pscat.c

@@ -0,0 +1,88 @@
+#include <ascii.h>
+#include <sysexits.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "libio.h"
+
+static char *program_name = "pscat";
+
+/* Originally designed to use parentheses but changed to brackets to escape the
+ * hassle of escaping them from the Bourne shell. */
+#define L_PAREN ASCII_LEFT_SQUARE_BRACKET
+#define R_PAREN ASCII_RIGHT_SQUARE_BRACKET
+
+/* Test string containing { c, '\0' } without iteration.
+ * Theoretically saves a little bit of time compared to strcmp(3). */
+int
+scmpflat(char *s, int c){
+	return
+		s[0] != '\0'
+		&& s[1] == '\0'
+		&& s[0] == c
+	;
+}
+
+/* Verifies arguments to pscat are sensible. */
+int
+check_arg(char **argv){
+	enum {
+		UNINITIALIZED = 0,
+		INLPAREN = 1,
+		NORMAL = 2
+	} s;
+	int terms;
+
+	for(s = UNINITIALIZED, terms = 0; *argv != NULL; ++argv)
+		switch(s){
+		case UNINITIALIZED: case NORMAL:
+			if(scmpflat(*argv, L_PAREN))
+				s = INLPAREN;
+			else
+				return 0; /* syntax error */
+			break;
+		case INLPAREN:
+			if(scmpflat(*argv, R_PAREN))
+				{ ++s; ++terms; }
+			break;
+		}
+
+	return terms;
+}
+
+int main(int argc, char *argv[]){
+	char *argv0;
+	char **psstart;
+	int child;
+	int i;
+	int retval;
+	int terms;
+
+	argv0 = argv[0] == NULL ? program_name : argv[0];
+	retval = 0;
+
+	if((terms = check_arg(++argv)) == 0){
+		write(2, "Usage: ", 7);
+		fdprint(2, argv0);
+		write(2, " \"[\" [utility [argument...]] \"]\" ...\n", 37);
+		return EX_USAGE;
+	}
+
+	/* loop starts with *argv -> the next L_PAREN */
+	for(i = 0; i < terms; ++i){
+		psstart = ++argv;
+		while(!scmpflat(*++argv, R_PAREN));
+		/* *argv -> the corresponding R_PAREN. turn it into NULL to
+		 * terminate the argument list to send to execvp(3) */
+		*argv = NULL;
+		if(fork() == 0){
+			execvp(psstart[0], psstart);
+		}else
+			wait(&child);
+		/* interpret status information from wait(2) */
+		if(WIFEXITED(child))
+			retval += WEXITSTATUS(child);
+		++argv;
+	}
+
+	return retval;
+}