From 98d1ccfa7ddeea5e0f7a760b9ced69d6f0ac5826 Mon Sep 17 00:00:00 2001
From: Jonas 'Sortie' Termansen <sortie@maxsi.org>
Date: Fri, 2 Mar 2012 18:02:31 +0100
Subject: [PATCH] Improved the shell with pipes, background processes and
 semicolons.

It's really hacky, but it's an improvement.
---
 utils/mxsh.cpp | 195 ++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 151 insertions(+), 44 deletions(-)

diff --git a/utils/mxsh.cpp b/utils/mxsh.cpp
index 5d0abc74..daa54207 100644
--- a/utils/mxsh.cpp
+++ b/utils/mxsh.cpp
@@ -10,6 +10,155 @@
 
 int status = 0;
 
+int runcommandline(const char** tokens)
+{
+	int result = 127;
+	size_t cmdnext = 0;
+	size_t cmdstart;
+	size_t cmdend;
+	bool lastcmd = false;
+	int pipein = 0;
+	int pipeout = 1;
+	int pipeinnext = 0;
+	char* const* argv;
+	size_t cmdlen;
+	const char* execmode;
+	const char* outputfile;
+	pid_t childpid;
+	bool internal;
+	int internalresult;
+readcmd:
+	cmdstart = cmdnext;
+	for ( cmdend = cmdstart; true; cmdend++ )
+	{
+		const char* token = tokens[cmdend];
+		if ( !token ||
+		     strcmp(token, ";") == 0 ||
+		     strcmp(token, "&") == 0 ||
+		     strcmp(token, "|") == 0 ||
+		     strcmp(token, ">") == 0 ||
+		     false )
+		{
+			break;
+		}
+	}
+
+	cmdlen = cmdend - cmdstart;
+	if ( !cmdlen ) { fprintf(stderr, "expected command\n"); goto out; }
+	execmode = tokens[cmdend];
+	if ( !execmode ) { lastcmd = true; execmode = ";"; }
+	tokens[cmdend] = NULL;
+
+	if ( strcmp(execmode, "|") == 0 )
+	{
+		int pipes[2];
+		if ( pipe(pipes) ) { perror("pipe"); goto out; }
+		if ( pipeout != 1 ) { close(pipeout); } pipeout = pipes[1];
+		if ( pipeinnext != 0 ) { close(pipeinnext); } pipeinnext = pipes[0];
+	}
+
+	outputfile = NULL;
+	if ( strcmp(execmode, ">") == 0 )
+	{
+		outputfile = tokens[cmdend+1];
+		if ( !outputfile ) { fprintf(stderr, "expected filename\n"); goto out; }
+		const char* nexttok = tokens[cmdend+2];
+		if ( nexttok ) { fprintf(stderr, "too many filenames\n"); goto out; }
+	}
+
+	cmdnext = cmdend + 1;
+	argv = (char* const*) (tokens + cmdstart);
+
+	internal = false;
+	internalresult = 0;
+	if ( strcmp(argv[0], "cd") == 0 )
+	{
+		internal = true;
+		const char* newdir = "/";
+		if ( argv[1] ) { newdir = argv[1]; }
+		if ( chdir(newdir) )
+		{
+			error(0, errno, "cd: %s", newdir);
+			internalresult = 1;
+		}
+	}
+	if ( strcmp(argv[0], "exit") == 0 )
+	{
+		int exitcode = argv[1] ? atoi(argv[1]) : 0;
+		exit(exitcode);
+	}
+
+	childpid = internal ? getpid() : fork();
+	if ( childpid < 0 ) { perror("fork"); goto out; }
+	if ( childpid )
+	{
+		if ( pipein != 0 ) { close(pipein); pipein = 0; }
+		if ( pipeout != 1 ) { close(pipeout); pipeout = 1; }
+		if ( pipeinnext != 0 ) { pipein = pipeinnext; pipeinnext = 0; }
+
+		if ( strcmp(execmode, "&") == 0 && !tokens[cmdnext] )
+		{
+			result = 0; goto out;
+		}
+
+		if ( strcmp(execmode, "&") == 0 || strcmp(execmode, "|") == 0 )
+		{
+			goto readcmd;
+		}
+
+		int status = internalresult;
+		if ( !internal && waitpid(childpid, &status, 0) < 0 )
+		{
+			perror("waitpid");
+			return 127;
+		}
+
+		if ( strcmp(execmode, ";") == 0 && tokens[cmdnext] && !lastcmd )
+		{
+			goto readcmd;
+		}
+
+		result = status;
+		goto out;
+	}
+
+	if ( pipeinnext != 0 ) { close(pipeinnext); }
+
+	if ( pipein != 0 )
+	{
+		close(0);
+		dup(pipein);
+		close(pipein);
+	}
+
+	if ( pipeout != 1 )
+	{
+		close(1);
+		dup(pipeout);
+		close(pipeout);
+	}
+
+	if ( outputfile )
+	{
+		close(1);
+		if ( open(outputfile, O_CREAT | O_WRONLY | O_TRUNC | O_APPEND) < 0 )
+		{
+			error(127, errno, "%s", outputfile);
+		}
+	}
+
+
+	execv(argv[0], argv);
+	error(127, errno, "%s", argv[0]);
+	return 127;
+
+out:
+	if ( pipein != 0 ) { close(pipein); }
+	if ( pipeout != 1 ) { close(pipeout); }
+	if ( pipeinnext != 0 ) { close(pipeout); }
+	return result;
+}
+
 void command()
 {
 	unsigned termmode = TERMMODE_UNICODE
@@ -75,51 +224,9 @@ void command()
 
 	if ( !argv[0] ) { return; }
 
-	if ( strcmp(argv[0], "exit") == 0 )
-	{
-		const char* status = "1";
-		if ( 1 < argc ) { status = argv[1]; }
-		exit(atoi(status));
-	}
-
-	if ( strcmp(argv[0], "cd") == 0 )
-	{
-		status = 0;
-		const char* newdir = "/";
-		if ( 1 < argc ) { newdir = argv[1]; }
-		if ( chdir(newdir) )
-		{
-			error(0, errno, "cd: %s", newdir);
-			status = 1;
-		}
-		return;
-	}
-
-	pid_t child = fork();
-	if ( child < 0 ) { perror("fork"); status = 1; return; }
-	if ( child != 0 )
-	{
-		pid_t childpid = wait(&status);
-		return;
-	}
-
-	if ( 3 <= argc )
-	{
-		if ( strcmp(argv[argc-2], ">") == 0 )
-		{
-			const char* file = argv[argc-1];
-			int outfd = open(file, O_CREAT | O_WRONLY | O_TRUNC | O_APPEND);
-			if ( outfd < 0 ) { error(127, errno, "%s", file); exit(127); }
-			close(1);
-			dup(outfd);
-			close(outfd);
-			argc -= 2;
-		}
-	}
-
 	argv[argc] = NULL;
-	execv(argv[0], (char* const*) argv);
-	error(127, errno, "%s", argv[0]);
+	status = runcommandline(argv);
+	return;
 }
 
 int main(int argc, char* argv[])