Self printing programs

A program that prints its own text.

Don't peek unless you are done working on the problem!

Answers by McKeeman

To make a program self-printing before it runs, in general prepend to the program two statements: a string assignment and a print statement. Within the string the whole program appears literally and also secretly in the form of a %s which will be filled in by the program string itself. One has to do a little work to get the line feeds and quotes right and make sure the requisite paraphernalia of program syntax are provided.

Here is a variety of solutions (of varying quality).

First, the easiest problem: the program only prints itself.

selfprint.c from the internet

+------------------------------------------------------------------------------+
|main(char*a){a="main(char*a){a=%c%s%c;printf(a,34,a,34);}";printf(a,34,a,34);}|
+------------------------------------------------------------------------------+

selfprint.c using the file system (cheap trick)

+-------------------------------------------+
|main(int a, char **argv) {printf(argv[1]);}|
+-------------------------------------------+

Compile it and then run it thusly

+-------------------------+
|a.out "`cat selfprint.c`"|
+-------------------------+

selfprint.m for an R13 MATLAB script.

+------+
|ans = |
|      |
|     3|
+------+

traditional selfprint.m for any MATLAB script.

+----------------------------------------------------------------+
|a='a=%c%s%c;fprintf(1,a,39,a,39,10);%c';fprintf(1,a,39,a,39,10);|
+----------------------------------------------------------------+

Now, suppose we have some quote-free script P.

selfprint.m for MATLAB script P:

+--------------------------------------------------------------------+
|a='a=%c%s%c;fprintf(1,a,39,a,39,10);P;%c';fprintf(1,a,39,a,39,10);P;|
+--------------------------------------------------------------------+

For any MATLAB script P:
```
+------+
|type P|
|P     |
+------+
```

For the unix shell csh, let file x contain

+-----+
|cat x| 
+-----+

and in csh do

+--------+
|source x|
+--------+

see also ~mckeeman/src/m ~mckeeman/src/c