I've moved these working programs into the src/other folder as they are

not strictly tools.

src/other/write_test.s

@@ -0,0 +1,61 @@
+" Test program for several system calls: open, read, write, close, exit
+" Do:
+"     ./as7 write_test.s > a.out
+"     ./a7out -d a.out
+main:
+   " Test the lac, dac instructions
+   lac in
+   dac out
+
+   " Write hello to fd1 i.e stdout
+   lac d1
+   sys write; hello; 7
+
+   " Test if the assembler can dac into a mid-line label
+   lac helloptr
+   dac 1f
+   lac d1
+   sys write; 1:0; 7
+
+   " Try to open file fred
+   sys open; fred; 0;
+
+   " read 5 words into the buffer from stdin: type in 10 or more characters!
+   lac d0
+   sys read; buf; 5
+
+   " Stop and dump memory, so you can see five words at location 0400
+   " Comment out the hlt instruction to test close and exit
+   hlt
+
+   " close stdin
+   lac d0
+   sys close
+
+   " exit
+   sys exit
+
+   " We should not get to the halt instruction
+   hlt
+
+
+" Some memory locations for lac and dac
+. = 0100
+in: 023
+
+. = 0200
+out: 0
+
+" Hello, world\n, two ASCII chars per word
+hello: <He>; <l 0154; 0157 ,>; 040; <wo>; <rl>; <d 012
+helloptr: hello
+
+" fred as a four word filename
+fred: <fr>; <ed>; 040040; 040040
+
+" Input buffer for read
+. = 0400
+buf: 0
+
+d0: 0
+d1: 1