#! perl5
#
# unwrap.pl Daniel Brockman 20030407 unwrap text lines
#
# Usage: unwrap.pl { {< file } | { file [...]} } > outfile

################################################
# The author grants permission to use for any  #
# purpose, including copying and modification, #
# provided the user acknowledges the author by #
# name.                                        #
# -- Daniel Brockman, author, 20031220         #
################################################

# unwrap.pl removes all newlines between nonempty lines.
# unwrap.pl replaces multiple empty lines with a single 
# empty line. unwrap.pl ignores empty lines preceding the 
# first nonempty line in the file.
# unwrap.pl reads the file sequentially, searching for a 
# nonempty line. On encountering a nonempty line, unwrap.pl
# appends succeeding nonempty lines to the first one in the
# set, replacing intervening white space with a single 
# space. On encountering an empty line or the end of the 
# file, unwrap.pl writes the concatenated line followed by 
# an empty line. Then unwrap.pl repeats the process, 
# searching for the next nonempty line.

my (
  $line,            # current line
  $lind,            # previous line
  $slug,            # aux
  $n,               # count of lines read
);

$lind="";           # init prev line
$n=0;               # init count
while($line=<>){    # while read new line
  $n++;             # incr count
  chop($line);      

  $slug=$line;             # avoid trashing line
  $slug=~s/[ \t\n]+// ;    # remove white space

  # print "AAA n:$n slug:$slug\n";
  
  if($slug eq ""){         # empty line?
    if($lind ne ""){       # prev line also empty?
      print "$lind\n";     # print prev line
      print "\n";          # print empty line
      $lind="";            # reinit prev line
    }
  
  }else{                   # nonempty line?
    $line=~s/[ \t\n]+$// ; # trim trailing white space

    if($lind eq ""){       # prev line empty?
      $lind=$line;         # cur line becomes prev line
    }else{                 # prev line not empty?
      $line=~s/^[ \t\n]+// ;   # remove leading white space
      $lind.=" ".$line ;       # append current line
    }
  }                            # end if slug eq ""
}                              # end while read new line

  
# end of file
print "$lind\n";     # print prev line
print "\n";          # print empty line

#