From 4425bfd45edfc4d2be18ce6d2a2eeb7ab80f7a6c Mon Sep 17 00:00:00 2001
From: Vicho <cibervicho@gmail.com>
Date: Thu, 1 May 2008 12:17:45 +0200
Subject: [PATCH] Added -n option to ifne.

With -n, ifne runs the command if the standard input is empty and does
nothing otherwise.
---
 ifne.c       | 56 +++++++++++++++++++++++++++++++++++++---------------
 ifne.docbook | 29 +++++++++++++++++++++++----
 2 files changed, 65 insertions(+), 20 deletions(-)

diff --git a/ifne.c b/ifne.c
index 817b1c5..a7abd21 100644
--- a/ifne.c
+++ b/ifne.c
@@ -22,23 +22,49 @@
 #include <unistd.h>
 #include <sys/wait.h>
 #include <sys/types.h>
+#include <string.h>
+#define streq(a, b) (!strcmp((a), (b)))
+
+static void stdin_to_stream(char *buf, ssize_t r, FILE *outf) {
+	while (r > 0) {
+		if (fwrite(buf, r*sizeof(char), 1, outf) < 1) {
+			fprintf(stderr, "Write error\n");
+			exit(EXIT_FAILURE);
+		}
+		r = read(0, buf, BUFSIZ*sizeof(char));
+	}
+	if (r == -1) {
+		perror("read");
+		exit(EXIT_FAILURE);
+	}
+}
 
 int main(int argc, char **argv) {
 	ssize_t r;
+	int run_if_empty;
+	char **argv_exec;
 	int fds[2];
 	int child_status;
 	pid_t child_pid;
 	char buf[BUFSIZ];
 	FILE *outf;
 
-	if (argc < 2) {
+	if ((argc < 2) || ((argc == 2) && streq(argv[1], "-n"))) {
 		/* Noop */
 		return EXIT_SUCCESS;
 	}
 
+	if (streq(argv[1], "-n")) {
+		run_if_empty = 1;
+		argv_exec = &argv[2];
+	} else {
+		run_if_empty = 0;
+		argv_exec = &argv[1];
+	}
+
 	r = read(0, buf, BUFSIZ*sizeof(char));
 
-	if (r == 0)
+	if ((r == 0) && !run_if_empty)
 		return EXIT_SUCCESS;
 	else if (r == -1) {
 		perror("read");
@@ -50,6 +76,13 @@ int main(int argc, char **argv) {
 		return EXIT_FAILURE;
 	}
 
+	if (r && run_if_empty) {
+		/* don't run the subcommand if we read something from stdin and -n was set */
+		/* But write stdin to stdout so ifne -n can be piped without sucking the stream */
+		stdin_to_stream(buf, r, stdout);
+		return EXIT_SUCCESS;
+	}
+
 	child_pid = fork();
 	if (!child_pid) {
 		/* child process: rebind stdin and exec the subcommand */
@@ -57,10 +90,10 @@ int main(int argc, char **argv) {
 		if (dup2(fds[0], 0)) {
 			perror("dup2");
 			return EXIT_FAILURE;
-                }
+		}
 
-		execvp(argv[1], &argv[1]);
-		perror(argv[1]);
+		execvp(*argv_exec, argv_exec);
+		perror(*argv_exec);
 		close(fds[0]);
 		return EXIT_FAILURE;
 	} else if (child_pid == -1) {
@@ -75,17 +108,8 @@ int main(int argc, char **argv) {
 		perror("fdopen");
 		exit(1);
 	}
-	do {
-		if (fwrite(buf, r*sizeof(char), 1, outf) < 1) {
-			fprintf(stderr, "Write error to %s\n", argv[1]);
-			exit(EXIT_FAILURE);
-		}
-		r = read(0, buf, BUFSIZ*sizeof(char));
-	} while (r > 0);
-	if (r == -1) {
-		perror("read");
-		exit(EXIT_FAILURE);
-	}
+
+	stdin_to_stream(buf, r, outf);
 	fclose(outf);
 
 	if (waitpid(child_pid, &child_status, 0) != child_pid) {
diff --git a/ifne.docbook b/ifne.docbook
index 92c7f48..38e3889 100644
--- a/ifne.docbook
+++ b/ifne.docbook
@@ -33,7 +33,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 			<firstname>Javier</firstname>
 			<surname>Merino</surname>
 		</author>
-		<date>2008-03-19</date>
+		<date>2008-05-01</date>
 	</refentryinfo>
 
 	<refmeta>
@@ -48,21 +48,42 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 	<refsynopsisdiv>
 		<cmdsynopsis>
-			<command>ifne command</command>
+			<command>ifne [-n] command</command>
 		</cmdsynopsis>
 	</refsynopsisdiv>
 	
 	<refsect1>
 		<title>DESCRIPTION</title>
 		
-                <para><command>ifne</command> runs the following command if and only if
-                the standard input is not empty.</para>
+		<para><command>ifne</command> runs the following command if and only if
+			the standard input is not empty.</para>
 	</refsect1>
 	
+	<refsect1>
+		<title>OPTIONS</title>
+
+		<variablelist>
+			<varlistentry>
+				<term><option>-n</option></term>
+				<listitem>
+					<para>Reverse operation. Run the command if the standard input is empty.</para>
+				</listitem>
+			</varlistentry>
+		</variablelist>
+	</refsect1>
+
 	<refsect1>
 		<title>EXAMPLE</title>
 		<cmdsynopsis>
 			<command>find . -name core | ifne mail -s "Core files found" root</command>
 		</cmdsynopsis>
 	</refsect1>
+
+	<refsect1>
+		<title>AUTHOR</title>
+
+		<para>Copyright 2008 by Javier Merino &lt;cibervicho@gmail.com&gt;</para>
+		<para>Licensed under the GNU GPL</para>
+	</refsect1>
+
 </refentry>
-- 
2.39.5