MGT Computer Solutions - Perl Excerpts

These snippets of Perl v.5 code are from routines which display individual pictures from a photo gallery. They develop the URLs for "previous" and "next" links that aid browsing single pictures in the gallery.

The following snippet only determines the required URLS.

#!/usr/bin/perl -w
use strict ;
use CGI ':standard';

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#calculate previous and next gallery item links
my ($Prev, $Next) = ("Previous", "Next");
my $GalleryFile = "+<../image.htm" ;
if ( $ImgPath eq "/cards/" ) { 
  $GalleryFile = "+<../card.htm" 
} 
#if we can't  open the gallery's html file, we are done with links
if (open(GALLERYFILE, $GalleryFile) ) {
  #complete list of gallery item links is right in the gallery's html file
  local $/;
  binmode(GALLERYFILE) ;
  my $FileBuf = <GALLERYFILE> ;
  close(GALLERYFILE) ;

  #pick out the links we want - look for neighbors of $EncodedURL
  if ( $FileBuf =~ m#cgi-bin(/v\.pl\?.{1,40}?nm=.{1,40}?)">.{1,300}?cgi-bin/v\.pl\?.{1,40}?nm=$EncodedURL"#s ) {
    $Prev = "<a href=.$1><strong>Previous</strong></a>" ;
  }
  if ( $FileBuf =~ m#cgi-bin/v\.pl\?.*?nm=$EncodedURL">.*?cgi-bin(/v\.pl\?.*?nm=.*?)"#s ) {
    $Next = "<a href=.$1><strong>Next</strong></a>" ;
  }

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The following snippet is from another version of the photo gallery routine. This version also parses the gallery URLs into an array for later reference.

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#calculate previous and next gallery item links
my ($Prev, $Next) = ('Previous', 'Next') ;

#define link count and pointer to current page for later reference
my ($count, $current) = (0, -1) ; 

#if we can't  open the gallery's html file, we are done with links
if (open(GALLERYFILE, "+<../image.htm") ) {
  #create list of gallery item links from gallery's html file
  local $/;
  binmode(GALLERYFILE) ;
  $FileBuf = <GALLERYFILE> ;
  close(GALLERYFILE) ;

  #split the file on "cgi directory/script name" because it's handy
  @arr = split(m#cgi-bin/#, $FileBuf) ;
  #lose the first piece as it starts with <html etc.
  shift @arr ;
  #remaining elements all start with the significant part of the desired url
  $count = (@arr) ;
  $FileBuf = '' ;

  #search the list for the current item's entry
  for (my $ix=0; $ix < $count; $ix++) {
    #clean up array entries as we go
    $arr[$ix] =~ s/>.*$//s ;
    # test for current page
    if ( $arr[$ix] =~ /=$EncodedItem"/ ) {
      #remember this location
      $current = $ix ;
    }
  }

  if ( $current != -1 ) {
    #current item found, build references for its neighbors
    if ( $current < $count - 1 )  {
      $Next = '<a href="./' . $arr[$current+1] . '><strong>Next</strong></a>' ;
    }
    if ( $current > 0 )  {
      $Prev = '<a href="./' . $arr[$current-1] . '><strong>Previous</strong></a>' ;
    }
  }

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