sudo apt-get install manpages-dev

sshfs shell.pas.rochester.edu:/home/tobin /home/tobin/ur

I am appalled at PINE's monthly offer to delete my sent mail. Fortunately this behavior can be stopped:

pruning-rule             =
            Set    Rule Values
            ---  ----------------------
            ( )  ask about rename, ask about deleting   (default)
            ( )  ask about rename, don't delete
            ( )  always rename, ask about deleting
            (*)  always rename, don't delete
            ( )  don't rename, ask about deleting
            ( )  don't rename, don't delete

How much mail do I send? (Yes, GNU sort offers a "--month-sort" option!)

$ grep --count --extended-regexp "^From " sent-mail-* |
> sed "s/sent-mail-\([a-z]*\)-\([0-9]*\):/\2 \1\t/g" |
> sort --key=2 --month-sort |
> sort --key=1 --numeric-sort --stable
2005 mar        325
2005 apr        205
2005 may        145
2005 jun        120
2005 jul        59
2005 aug        43
2005 sep        67
2005 oct        46
2005 nov        127
2005 dec        201
2006 jan        330
2006 feb        366
2006 mar        297
2006 apr        208
2006 may        245
2006 jun        109
2006 jul        258

That could doubtlessly be condensed a little by changing the field separator to sort (eliminating the need for sed) and combining the two sort commands.

Reading some text on writing secure unix programs, I learned that the unix environment (or a copy thereof) is stored as a simple array of strings (ie, char **) pointed to by the variable environ defined in unistd.h. Each string is just in the format ``name=value''. Remarkably primitive, eh? Anyway, you can dump the environment quite simply:

#include <unistd.h>
#include <stdio.h>

extern char **environ;

int main(void) {
  for (char **foo = environ; foo && *foo; foo++) 
    printf("\"%s\"\n",*foo);
  return 0; 
}

Here's something else I didn't know. The ``%n'' format specifier directs printf to write the number of bytes written so far into the corresponding variable in the argument list. Example:

#include <stdio.h>

int main(void) {
  int foo;
  printf("This is a test message.\n%n",&foo);
  printf("The above message contained %d bytes.\n",foo);
  return 0;
}

The following code snippet uses a buffer overflow to change the return address of main(). That's right, main() apparently is called by some function in the C library, so it has a real return address. The stack grows towards lower memory addresses, so we can find the return address by allocating a word (buffer[0]) on the stack; skip one word (the stack pointer) after that allocated word, and the next (ie, buffer[2]) will coincide with the saved return address. Then we can just change it so something else.

#include <stdio.h>

void albatross(void) {
  printf("albatross!\n");
  exit(0);
}

int main(void) {
  int buffer[1];
  buffer[2] = (int)albatross;
  return 0;
}