Making a Snoopy calendar in Unix

For those of you who don’t know, the Snoopy calendar is a gimmick of the hacker culture. It basically refers to a line printer calendar for 1969 featuring the iconic beagle from Peanuts, that apparently hangs on the wall of every Real Programmer’s office. I’m not entirely certain of the origins of this meme, but it dates back at least to the humorous essay Real Programmers Don’t Use Pascal, which was posted to Usenet back in 1983.

snoopy

I have a certain fondness for this particular gimmick which I can’t quite explain. Perhaps it is the fact that it provides a feasible and exciting challenge for me – that of making my own Snoopy calendar. I have actually done this a couple of times.  This time I used a combination of C programming and several Unix programs like enscript, figlet, cal, and sed.

There are three components to the Snoopy calendar. The first is the Snoopy ASCII/line printer art, the second is the calendar, and the third is the year number banner. These components must be pasted together in the same text file, which can then be converted to Postscript for printing. The Unix paste program is not satisfactory for this, since it doesn’t align the text, so I wrote my own program. Here is the final result:


  1 /*************************************************
  2  * Paste V. 1.0                                  *
  3  *                                               *
  4  * Description: Pastes two files side-by-side    *
  5  * with the edges aligned.  Does not work with   *
  6  * files that contain tabs.                      *
  7  *                                               *
  8  * Author: Michael Warren                        *
  9  * License: Micheal Warren Free Software License *
 10  * Date: November 13, 2016                       *
 11  *************************************************/
 12 
 13 
 14 #include <stdio.h>
 15 #include <stdlib.h>
 16 #include <string.h>
 17 #include <errno.h>
 18 
 19 // Maximum line length
 20 #ifndef _MAXLL_
 21 # define _MAXLL_ 80
 22 #endif
 23 
 24 struct line{
 25         int linenum;
 26         int linelen;
 27         char text[_MAXLL_]; // Text of line
 28         struct line *next;  // Next line in current file
 29         struct line *corr;  // Corresponding line in other file
 30 };
 31 
 32 struct line *topl; // Top of left file
 33 struct line *topr; // Top of right file
 34 struct line *curl; // Current line in left file
 35 struct line *curr; // Current line in right file
 36 
 37 int mainint argc, char **argv ){
 38         FILE *l, *r;                // left and right files
 39         int llen = 0, rlen = 0;     // Number of lines in each file
 40         int rmaxll = 0, lmaxll = 0// Length of longest line in each file
 41         if( !argv[1] || !argv[2] ){
 42                 printf"\nUsage:\n%s <leftfile> <rightfile>\n\n", argv[0] );
 43                 return 1;
 44         }
 45         if( (l = fopen( argv[1], "r" )) == NULL ){
 46                 fprintfstderr"%s: ", argv[0] );
 47                 switch( errno ){
 48                         case EPERM   : fprintfstderr"Operation not permitted.\n" ); break;
 49                         case ENOENT  : fprintfstderr"%s: No such file or directory.\n", argv[1] ); break;
 50                         case EINTR   : fprintfstderr"Interrupted system call.\n" ); break;
 51                         case EIO     : fprintfstderr"Input/outpur error.\n" ); break;
 52                         case EDEADLK : fprintfstderr"Deadlock avoided.\n" ); break;
 53                         case ENOMEM  : fprintfstderr"Cannot allocate memory.\n" ); break;
 54                         case EACCES  : fprintfstderr"Permission denied.\n" ); break;
 55                         case ENODEV  : fprintfstderr"Operation not supported by device.\n" ); break;
 56                         case EISDIR  : fprintfstderr"%s is a directory.\n", argv[1] ); break;
 57                         case EINVAL  : fprintfstderr"%s: Invalid argument.\n", argv[1] ); break;
 58                         case ENFILE  : fprintfstderr"Too many open files in system.\n" ); break;
 59                         case EMFILE  : fprintfstderr"Too many open files.\n" ); break;
 60                         case EFBIG   : fprintfstderr"File %s is too large.\n", argv[1] ); break;
 61                         default      : fprintfstderr"An error occurred.  Error #: %d\n", errno );
 62                 }
 63                 return errno;
 64         }
 65         if( (r = fopen( argv[2], "r" )) == NULL ){
 66                 fprintfstderr"%s: ", argv[0] );
 67                 switch( errno ){
 68                         case EPERM   : fprintfstderr"Operation not permitted.\n" ); break;
 69                         case ENOENT  : fprintfstderr"%s: No such file or directory.\n", argv[2] ); break;
 70                         case EINTR   : fprintfstderr"Interrupted system call.\n" ); break;
 71                         case EIO     : fprintfstderr"Input/outpur error.\n" ); break;
 72                         case EDEADLK : fprintfstderr"Deadlock avoided.\n" ); break;
 73                         case ENOMEM  : fprintfstderr"Cannot allocate memory.\n" ); break;
 74                         case EACCES  : fprintfstderr"Permission denied.\n" ); break;
 75                         case ENODEV  : fprintfstderr"Operation not supported by device.\n" ); break;
 76                         case EISDIR  : fprintfstderr"%s is a directory.\n", argv[2] ); break;
 77                         case EINVAL  : fprintfstderr"%s: Invalid argument.\n", argv[2] ); break;
 78                         case ENFILE  : fprintfstderr"Too many open files in system.\n" ); break;
 79                         case EMFILE  : fprintfstderr"Too many open files.\n" ); break;
 80                         case EFBIG   : fprintfstderr"File %s is too large.\n", argv[2] ); break;
 81                         default      : fprintfstderr"An error occurred.  Error #: %d\n", errno );
 82                 }
 83                 return errno;
 84         }
 85         topl = (struct line *) mallocsizeofstruct line ) );
 86         topr = (struct line *) mallocsizeofstruct line ) );
 87         curl = topl; curr = topr;
 88         char c;
 89         // Build left file:
 90         while( (c = fgetc( l )) != EOF ){
 91                 ungetc( c, l );
 92                 curl->next = (struct line *) mallocsizeofstruct line ) );
 93                 curl = curl->next;
 94                 fgets( curl->text, _MAXLL_, l );
 95                 curl->linelen = strlen( curl->text );
 96                 lmaxll = (lmaxll < curl->linelen)?(curl->linelen):lmaxll;
 97                 curl->text[strlen( curl->text )-1] = '\0';
 98                 curl->linenum = ++llen;
 99         }
100         // Build right file:
101         while( (c = fgetc( r )) != EOF ){
102                 ungetc( c, r );
103                 curr->next = (struct line *) mallocsizeofstruct line ) );
104                 curr = curr->next;
105                 fgets( curr->text, _MAXLL_, r );
106                 curr->linelen = strlen( curr->text );
107                 rmaxll = (rmaxll < curr->linelen)?(curr->linelen):rmaxll;
108                 curr->text[strlen( curr->text )-1] = '\0';
109                 curr->linenum = ++rlen;
110         }
111         const int llenc = llen;
112         const int rlenc = rlen;
113         // Extend right file if shorter:
114         if( llen > rlen ){
115                 int diff = llen - rlen;
116                 forint i = 0; i < diff; i++ ){
117                         curr->next = (struct line *) mallocsizeofstruct line ) );
118                         curr = curr->next;
119                         forint j = 0; j < rmaxll; j++ ){
120                                 (curr->text)[j] = ' ';
121                         }
122                         (curr->text)[rmaxll] = '\0';
123                         curr->linenum = ++rlen;
124                 }
125         }
126         // Extend left file if shorter:
127         else if( llen < rlen ){
128                 int diff = rlen - llen;
129                 forint i = 0; i < diff; i++ ){
130                         curl->next = (struct line *) mallocsizeofstruct line ) );
131                         curl = curl->next;
132                         forint j = 0; j < lmaxll; j++ ){
133                                 (curl->text)[j] = ' ';
134                         }
135                         (curl->text)[lmaxll] = '\0';
136                         curl->linenum = ++llen;
137                 }
138         }
139         // Begin paste operation
140         curl = topl; curr = topr;
141         unsigned int len = (llenc < rlenc )?llenc:rlenc;
142         forint i = 0; i < len; i++ ){
143                 curl = curl->next;
144                 curr = curr->next;
145                 printf"%s  ", curl->text );
146                 int lendif = lmaxll - curl->linelen;
147                 forint j = 0; j < lendif; j++ ){
148                         putchar' ' );
149                 }
150                 printf"%s", curr->text );
151                 lendif = rmaxll - curr->linelen;
152                 forint j = 0; j < lendif; j++ ){
153                         putchar' ' );
154                 }
155                 putchar'\n' );
156         }
157         while( (curl = curl->next) != NULL ){
158                 curr = curr->next;
159                 printf"%s %s\n", curl->text, curr->text );
160         }
161         // Cleanup:
162         curl = topl->next; curr = topr->next;
163         while( curl != NULL ){
164                 struct line *auxl = curl->next;
165                 free( curl );
166                 curl = auxl;
167         }
168         while( curr != NULL ){
169                 struct line *auxr = curr->next;
170                 free( curr );
171                 curr = auxr;
172         }
173         free( topl ); free( topr ); fclose( l ); fclose( r );
174         return 0;
175 }

I created the banner using the following command:


figlet -f banner 1969 | sed "s/ /  /g" | sed "s/#/##/g" | sed "p"

The three sed commands are there to double the width and height of the banner. It results in the following output:


    ##        ##########      ##########      ##########    
    ##        ##########      ##########      ##########    
  ####      ##          ##  ##          ##  ##          ##  
  ####      ##          ##  ##          ##  ##          ##  
##  ##      ##          ##  ##              ##          ##  
##  ##      ##          ##  ##              ##          ##  
    ##        ############  ############      ############  
    ##        ############  ############      ############  
    ##                  ##  ##          ##              ##  
    ##                  ##  ##          ##              ##  
    ##      ##          ##  ##          ##  ##          ##  
    ##      ##          ##  ##          ##  ##          ##  
##########    ##########      ##########      ##########    
##########    ##########      ##########      ##########    


I then did some manual editing to round out the corners. I put this output above the output of cal -y 1969 in Vim, and then ran the program that I had written to paste it onto a Snoopy ASCII picture (I used a different picture this time). I then ran it through enscript, using landscape orientation and reducing the text size to it would all fit on one page, and also telling it to run in line printer emulation mode.

The final result:

snoopy4-cal

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BSD Unix hack: adding conditional preprocessing capabilities to calendar

One of the most useful features of the GNU Compiler Collection is the -D option to cpp, which allows you to define macros at the command line. This in combination with #ifdefs and #ifndefs in the C/C++ source files allows for very versatile conditional compilation, because it allows you to set certain parameters that the program uses without having to edit the original source code. You can use this to, say, compile a debugging version of a program, among other things.

It is widely known that the C/C++ languages use CPP for preprocessing. What is less well-known is the fact that calendar, the default BSD reminder program, also uses CPP. This is one advantage that calendar has over the newer and more feature-rich remind program, which, as far as I know, doesn’t use preprocessing. calendar is available for all major BSD variants, including macOS. It may have been ported to other *NIXs such as Linux, though I am not sure, and I don’t feel like looking it up right now.

calendar uses CPP to allow for the conditional inclusion of several libraries of pre-written reminders or events – from the standard run-of-the-mill dates like US holidays and birthdays of famous people, to more exotic things like important events in the history of computing, and important dates in the Lord of the Rings timeline. This is done in the obvious way:


# include <calendar.usholiday>
# include <calendar.birthday>
# include <calendar.computer>
# include <calendar.lotr>

You can also do #defines, with or without parameters:


#define PHYSICAL( TIME ) Appointment with -NAME REMOVED- for yearly physical at TIME
#define PSYCH_APPT( TIME ) Appointment with -NAME REMOVED- at TIME
#define THERAPY( TIME ) Therapy appointment with -NAME REMOVED- at TIME

...

Jul 20  PSYCH_APPT( 3:00 PM )
Nov 15  PHYSICAL( 11:00 AM )
Nov 29  THERAPY( 2:00 PM )

Unfortunately, that’s about all you can do with CPP in the default calendar program. I decided I wanted to be able to include certain libraries conditionally, so that if I want to just view reminders for things I have to do in my own life, I have that option, and if I want to also check on upcoming holidays, or events in Tolkien’s universe, I can manipulate those options with a simple command line flag. The CPP code in my calendar file would then look something like this:


#ifdef _HOL_
# include <calendar.usholiday>
#endif

#ifdef _BDAY_
# include <calendar.birthday>
#endif

#ifdef _COMP_
# include <calendar.computer>
#endif

#ifdef _LOTR_
# include <calendar.lotr>
#endif

… And I would manipulate these options from the command line using a parameter like -D_COMP_.

So I got to work writing a frontend for calendar that adds that capability. Here is the result, written in bash and sed:


#!/usr/bin/env bash
# This script is a frontend for the calendar program that adds the
# full power of cpp to calendar.  Namely, it can do conditional
# preprocessing and #includes based on arguments given by the -D
# option to CPP.

declare -i DAYS=10

# Parse command line options:
for arg in "$@"
do
        case "$arg" in
                -W ) shift; let DAYS=$1; shift;;
                -B ) shift; let DAYS=-$1; shift;;
                -D ) shift; break;; # Define CPP macros
                -* ) shift; shift;;
        esac
done

# Debugging info:
#echo "DAYS=$DAYS"
#echo "\$1=$1"
#echo "\$2=$2"

# Preprocess calendar file and run it through a sed script that performs necessary edits
cpp -D${1:-"NULL1"} -D${2:-"NULL2"} -D${3:-"NULL3"} -D${4:-"NULL4"} -I /usr/share/calendar ~/.calendar/calendar 2>/dev/null | sed -f ~/Scripts/calendar.sed >| ~/calendar.tmp


# Print output of calendar
if [[ $DAYS -gt 0 ]]
then
        # Print forward
        command calendar -f ~/calendar.tmp -W $DAYS
elif [[ $DAYS -lt 0 ]]
then
        # Print backward
        let DAYS=-$DAYS
        command calendar -f ~/calendar.tmp -B $DAYS
fi

# Cleanup
rm ~/calendar.tmp
unset arg DAYS

The accompanying sed script:


#!/usr/bin/env sed

/^#/d
/^[0-9][0-9]*\/[0-9][0-9]* /s/ /\       /
/^[A-Z][a-z]* [0-9][0-9]* /{
        s/ /\   /
        s/ /\   /
        s/\     / /
}

After this I set an alias in my .bashrc file to have the calendar command run this script, rather than running the calendar program directly.

There are some problems with this script, the main one being that it is extremely slow, sometimes taking as long as 10-15 seconds to do the preprocessing. If I rewrote this program in C, I could speed it up by a few orders of magnitude, not only because C is inherently faster, but also because it exposes more of the underlying details of how everything is implemented, which allows you to program more intelligently and optimize your program for the hardware.

For example, I don’t know for sure whether comparing two integers is faster than comparing two strings in the bash shell (a problem I ran into here when trying to decide whether to just use a “true”/”false” string to determine whether to use -B or -W; the bash shell doesn’t have Boolean types), because I don’t understand the underlying implementation. I would have to spend days studying the source code for the shell to get a sense of how to optimize everything. All I know is that all shell variables are essentially strings, so it’s not the same as C, where comparing two integers is much faster than going through two character arrays and comparing each pair of characters one by one. In the bash shell, you have to convert the numerical strings to numbers, perform an arithmetic or comparison operation on them, and then convert them back to strings. Both methods are extremely inefficient. This is what I don’t like about extremely high-level scripting languages such as Unix shell, Python, Ruby, PHP, etc. But hey, they allow you to write programs a hell of a lot faster than C, which is better if you just want a quick-and-dirty solution to a programming problem.