first commit

.gitignore

@@ -0,0 +1,2 @@
+*.o
+/rot13

Makefile

@@ -0,0 +1,9 @@
+CC=      tcc
+CFLAGS=  -Wall -Wextra -Werror
+LDFLAGS= -s
+
+all: rot13
+%: %.c
+	$(CC) $^ -o $@ $(CFLAGS) $(LDFLAGS)
+clean:
+	$(RM) *.o rot13

rot13.c

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+#include<unistd.h>
+#include<fcntl.h>
+int main(int argc,char**argv)
+{
+
+	int fd=0;
+
+	if(argc>1)
+	{
+		fd=open(argv[1],O_RDONLY);
+		if(fd<0)
+		{
+			write(2,"failed to open file\n",20);
+			fd=0;
+		}
+	}
+
+	int c;
+	while(read(fd,&c,1))
+	{
+		if(c>='a'&&c<='z')
+			c=((c-'a')+13)%26+'a';
+		else if(c>='A'&&c<='Z')
+			c=((c-'A')+13)%26+'A';
+		else if(c>='0'&&c<='9')
+			c=((c-'0')+10)%10+'0';
+		write(1,&c,1);
+	}
+}