Shell Programming Question - sort

[Brad Appleton]

Sorry to post this to the net but I couldnt successfully send mail!

In article <751 at ncs.dnd.ca> Gordon Marwood writes:
>I am trying to sort (using "sort" in Ultrix) based on the last two
>characters in a line (which are numeric).  There are a variable number
>of characters in a line, and these last two characters are preceded by a
>space, there are also a variable number of spaces in a line, so the
>number of fields will be variable if space is used as the field
>separator.  None of my available texts gives me a clue as to whether a
>sort can be done based on the last field in a line, regardless of the
>number of fields in the line.  Is there any "sort" option that can 
>do this ?
>
>Gordon Marwood
>Internet: marwood at ncs.dnd.ca

If I knew what you are trying to achieve (with sort) I might be able
to provide better assistance! All I can suggest is:

1) see if you can get to the last field using $NF in awk

2) (probably better than #1 ...)

I believe that BSD Unix should have a command called "reverse" which
reverses the characters in each line of a file. Run your file through
reverse, then sort, then back through reverse (this may not work 
depending upon how fancy a sort you need to do).

	reverse file | sort [options] | reverse [-] > outfile

Just in case you dont have reverse... It is easy to write! The following
did just fine for me on Xenix (it is not a superlatively written piece of 
code but it performs a simple job, and it works (on Xenix anyway :-):

------------------cut here----------------------cut here----------------
/**
* reverse.c -- C source to reverse the characters in the lines of one
*              or more files.
*
*  NAME
*      reverse -- reverse the characters in each line of input
*
*  SYNOPSIS
*      reverse  [-]|[ filename ... ]
*
*  DESCRIPTION
*      Reverse will each line of input and print the resultant line on
*      the standard output. If "-" is given as a filename, then input is 
*      taken from the standard input. Actually, "-" may be listed as one
*      of several filenames and, at that time, stdin will be used for input
*      (after the previous files) and then will continue with the remaining
*      files. I have not tried this out however!
*
*  Created Mar '89 by Brad Appleton
*
*  Mar 8 '90, Brad Appleton -- made same minor additions of #defines and
*                              subroutines in order to not require my own
*                              personal .h files
**/

#ifndef TRUE
#define  TRUE  1
#define  FALSE 0
#endif

#define  USE_STDIN "-"
#define  LINE_LEN  512		/* make this as big as you need */

#include <stdio.h>

/* ckopen -- open file; check for success */
FILE *ckopen( filename, filemode )  char *filename, *filemode;
{
   FILE *fopen(), *fp;

   if ( (fp = fopen( filename, filemode )) == NULL ) {
     fprintf( stderr, "reverse: unable to open %s\n", filename );
     exit( 2 );
   }/* if */

   return  (fp);
}/* ckopen() */


/* reverse -- reverse the chars in a string (but not the newline) */
void  reverse( str )  char *str;
{
  char  hold;
  int   i, j, append = FALSE, len = strlen( str );

  if ( str[ len -1 ] == '\n' )  {
    str[ --len ] = '\0';
    append = TRUE;
  } /* if new-line */

  for ( i = 0, j = (len -1 ) ; i <= j ; i++, j-- )  {
      /* swap( str[i], str[j] ) */
    hold   = str[i];
    str[i] = str[j];
    str[j] = hold;
  }/* for */

  if ( append )    str[ len ] = '\n';

}/* reverse() */


main( argc, argv )  int argc; char *argv[];
{
  int  i;
  char line[ LINE_LEN ];
  FILE *infile;

  if ( argc == 1 )  {  /* print usage and exit */
    fprintf( stderr, "usage:  remind  [-]|[filename ...]\n" );
    exit( 1 );
  }/* if no args */

  /* process each file in the order given on the command line */
  for ( i = 1 ; i < argc ; i++ )  {
    if ( ! strcmp( argv[i], USE_STDIN ) )
      infile = stdin;
    else
      infile = ckopen( argv[i], "r" );

    while ( fgets( line, LINE_LEN, infile ) != NULL )  {
      reverse( line );
      fputs( line, stdout );
    }/* while */
  }/* for each arg */

  exit( 0 );
}/* main */
----------------finish cut---------------------finish cut-----------------------

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