cumsum

#!/usr/bin/perl
# $Id$

# cumulative sum:
#  given a file like
#
#   a1  text
#   a2  text
#    .  text
#    .  text
#   aN  text
#
# outputs  'sI  aI  text' for each,
# where sI is the sum 1..I
#

# NOTE:  this only reads digits chars to make integers.
# minus sign is not matched (though a simple regexp mod)
# same for floats (regexp & optionally print format)

$sum = 0;
while (<>) {
  if ( /^\s*(\d+)\s*/ ) {
    $sum += $1;
  }
#  printf "%6d\t$_",$sum;
# 'd' converts to an int and causes truncation...  
# since $sum is known to be an int, %s is equivalent without
# these shortcomings.
  printf "%7d\t%s",$sum, $_;
}