From 9a95b64618a1d3dfce4cb15874161636636de862 Mon Sep 17 00:00:00 2001
From: dtb <trinity@trinity.moe>
Date: Tue, 19 Jul 2022 16:52:28 -0400
Subject: [PATCH] pscat(1)

---
 .gitignore  |  1 +
 Makefile    |  7 +++++
 man/pscat.1 | 33 ++++++++++++++++++++
 src/pscat.c | 88 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 129 insertions(+)
 create mode 100644 man/pscat.1
 create mode 100644 src/pscat.c

diff --git a/.gitignore b/.gitignore
index eeb8b1a..6c1976f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,6 +4,7 @@ bin/id
 bin/lowercase
 bin/nonzero
 bin/nutshell
+bin/pscat
 bin/rldecode
 bin/rlencode
 bin/roll
diff --git a/Makefile b/Makefile
index 54d49c0..91e6dff 100644
--- a/Makefile
+++ b/Makefile
@@ -25,6 +25,7 @@ cleanprograms:
 	$(RM) bin/mm
 	$(RM) bin/multiply
 	$(RM) bin/nonzero
+	$(RM) bin/pscat
 	$(RM) bin/simexec
 	$(RM) bin/sleep
 	$(RM) bin/streq
@@ -90,6 +91,12 @@ nutshell.o: libio usefulmacros src/nutshell.c src/nutshell.h src/nutshell_builti
 nutshell: libio nutshell.o
 	$(CC) $(CFLAGS) -o bin/nutshell build/libio.o build/nutshell.o
 
+pscat.o: libio src/pscat.c
+	$(CC) $(CFLAGS) -c -o build/pscat.o src/pscat.c
+
+pscat: libio pscat.o
+	$(CC) $(CFLAGS) -o bin/pscat build/libio.o build/pscat.o
+
 roll.o: lib/libio.h src/roll.c sysexits
 	$(CC) $(CFLAGS) -c -o build/roll.o src/roll.c
 
diff --git a/man/pscat.1 b/man/pscat.1
new file mode 100644
index 0000000..43ad775
--- /dev/null
+++ b/man/pscat.1
@@ -0,0 +1,33 @@
+.TH PSCAT 1
+
+.SH NAME
+
+pscat \- concatenate the output of processes
+
+.SH SYNOPSIS
+
+pscat
+"[" 
+.RB [ utility
+.RB [ argument... ]]
+"]" ...
+
+.SH DESCRIPTION
+
+Pscat executes multiple commands, one after the other.
+This allows multiple processes to be piped as one to another program.
+
+.SH DIAGNOSTICS
+
+Pscat will print an error message and exit with the appropriate status from sysexits(3) if executed improperly.
+Pscat will exit with the sum of the child processes' exit statuses if run correctly.
+
+.SH BUGS
+
+Pscat's exit status isn't useful when run correctly; there's no way to tell which process failed if one did.
+This issue of ergonomics isn't obviously mendable as processes' standard outputs and standard errors are meant to both be conveyed.
+If either could be ignored the individual exit statuses could simply be printed.
+
+.SH COPYRIGHT
+
+Public domain.
diff --git a/src/pscat.c b/src/pscat.c
new file mode 100644
index 0000000..ad8c2bd
--- /dev/null
+++ b/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;
+}