utils-std

commit: 69cbb114a926327ac256e2007d4208ba734e1fad
parent 51df2fb18fab83c6ccae6e4ddeb9e00b40740e64
Author: Haelwenn (lanodan) Monnier <contact@hacktivis.me>
Date:   Thu,  5 Feb 2026 11:37:55 +0100

cmd/tee: Use read/write instead of fgetc/fputc

Prevents buffering of the output (short read means immediate write)
and potentially increase performance (reduced processing,
better buffer size).

Diffstat:
M
cmd/tee.c
43
+++++++++++++++++++++++++++----------------

1 file changed, 27 insertions(+), 16 deletions(-)
diff --git a/cmd/tee.c b/cmd/tee.c
@@ -8,8 +8,9 @@
 
 #include <assert.h> /* assert() */
 #include <errno.h>  /* errno */
+#include <fcntl.h>
 #include <signal.h> /* signal() */
-#include <stdio.h>  /* fprintf(), fgetc(), fputc(), fclose(), fopen() */
+#include <stdio.h>  /* fprintf() */
 #include <stdlib.h> /* calloc(), free(), abort() */
 #include <string.h> /* strerror() */
 #include <unistd.h> /* getopt(), opt… */
@@ -20,19 +21,16 @@
 const char *argv0 = "tee";
 
 static void
-cleanup(FILE **fds)
+cleanup(int *fds)
 {
-	if(fds != NULL)
-	{
-		free(fds);
-	}
+	free(fds);
 }
 
 int
 main(int argc, char *argv[])
 {
-	const char *mode = "w";
-	FILE **fds = {NULL}; // Shut up GCC
+	mode_t mode = O_WRONLY | O_NOCTTY | O_CREAT;
+	int *fds = NULL;
 	int c;
 
 #ifdef HAS_GETOPT_LONG
@@ -54,7 +52,7 @@ main(int argc, char *argv[])
 		switch(c)
 		{
 		case 'a':
-			mode = "a";
+			mode |= O_APPEND;
 			break;
 		case 'i': /* ignore SIGINT */;
 			signal(SIGINT, SIG_IGN);
@@ -88,9 +86,9 @@ main(int argc, char *argv[])
 		assert(argv[argi]);
 
 		// POSIX: implementations shouldn't treat '-' as stdin
-		fds[argi] = fopen(argv[argi], mode);
+		fds[argi] = open(argv[argi], mode);
 
-		if(fds[argi] == NULL)
+		if(fds[argi] < 0)
 		{
 			fprintf(stderr, "tee: error: Failed opening file ‘%s’: %s\n", argv[argi], strerror(errno));
 			cleanup(fds);
@@ -101,9 +99,21 @@ main(int argc, char *argv[])
 	// main loop, note that failed writes shouldn't make tee exit
 	int err = 0;
 
-	while((c = fgetc(stdin)) != EOF)
+	while(true)
 	{
-		if(fputc(c, stdout) == EOF)
+		static char buf[BUFSIZ];
+		ssize_t sread = read(STDIN_FILENO, buf, sizeof(buf));
+		if(sread == 0) break;
+		if(sread < 0)
+		{
+			fprintf(stderr, "tee: error: Failed reading from stdin: %s\n", strerror(errno));
+			cleanup(fds);
+			return 1;
+		}
+
+		size_t nread = (size_t)sread;
+
+		if(write(STDOUT_FILENO, buf, nread) < 0)
 		{
 			fprintf(stderr, "tee: error: Failed writing to stdout: %s\n", strerror(errno));
 			err = 1;
@@ -112,9 +122,10 @@ main(int argc, char *argv[])
 
 		for(int argi = 0; argi < argc; argi++)
 		{
-			if(fputc(c, fds[argi]) == EOF)
+			if(write(fds[argi], buf, nread) < 0)
 			{
-				fprintf(stderr, "tee: error: Failed writing to argument %d: %s\n", argi, strerror(errno));
+				fprintf(
+				    stderr, "tee: error: Failed writing to file '%s': %s\n", argv[argi], strerror(errno));
 				err = 1;
 				errno = 0;
 			}
@@ -124,7 +135,7 @@ main(int argc, char *argv[])
 	// cleanup
 	for(int argi = 0; argi < argc; argi++)
 	{
-		if(fclose(fds[argi]) != 0)
+		if(close(fds[argi]) != 0)
 		{
 			fprintf(stderr, "tee: error: Failed closing file '%s': %s\n", argv[argi], strerror(errno));
 			err++;