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Full Discussion: While read
Top Forums Shell Programming and Scripting While read Post 303014119 by Yoda on Monday 5th of March 2018 12:26:01 PM
Old 03-05-2018
The reason is when you pipe the file to a while loop, it actually gets executed in a sub-shell:-
Code:
cat $1 | while read line

So the scope of the variable sum value is within the while loop. This is the reason why it prints 0 outside the while loop

You can resolve this by removing the pipe:-
Code:
sum=0
while read line
do
#set $line
sum=`expr $sum  +  1`
done < "$1"
echo $sum

These 2 Users Gave Thanks to Yoda For This Post:
Ghassen Scott
 

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LEARN ABOUT SUSE

sum

sum(n)							     Cyclic Redundancy Checks							    sum(n)

__________________________________________________________________________________________________________________________________________________

NAME

       sum - Calculate a sum(1) compatible checksum

SYNOPSIS

       package require Tcl  8.2

       package require sum  ?1.1.0?

       ::crc::sum ?-bsd | -sysv? ?-format fmt? ?-chunksize size? [ -filename file | -channel chan | string ]

_________________________________________________________________

DESCRIPTION

       This  package  provides	a Tcl-only implementation of the sum(1) command which calculates a 16 bit checksum value from the input data.  The
       BSD sum algorithm is used by default but the SysV algorithm is also available.

COMMANDS

       ::crc::sum ?-bsd | -sysv? ?-format fmt? ?-chunksize size? [ -filename file | -channel chan | string ]
	      The command takes string data or a file name or a channel and returns a checksum value calculated using the  sum(1)  algorithm.  The
	      result is formatted using the format(n) specifier provided or as an unsigned integer (%u) by default.

OPTIONS

       -sysv  The SysV algorithm is fairly naive. The byte values are summed and any overflow is discarded. The lowest 16 bits are returned as the
	      checksum.  Input with the same content but different ordering will give the same result.

       -bsd   This algorithm is similar to the SysV version but includes a bit rotation step which provides a dependency on the order of the  data
	      values.

       -filename name
	      Return a checksum for the file contents instead of for parameter data.

       -channel chan
	      Return  a  checksum  for	the  contents  of the specified channel. The channel must be open for reading and should be configured for
	      binary translation. The channel will no be closed on completion.

       -chunksize size
	      Set the block size used when reading data from either files or channels. This value defaults to 4096.

       -format string
	      Return the checksum using an alternative format template.

EXAMPLES

       % crc::sum "Hello, World!"
       37287

       % crc::sum -format 0x%X "Hello, World!"
       0x91A7

       % crc::sum -file sum.tcl
       13392

AUTHORS

       Pat Thoyts

BUGS, IDEAS, FEEDBACK
       This document, and the package it describes, will undoubtedly contain bugs and other problems.  Please report such in the category  crc	of
       the  Tcllib  SF	Trackers [http://sourceforge.net/tracker/?group_id=12883].  Please also report any ideas for enhancements you may have for
       either package and/or documentation.

SEE ALSO

       cksum(n), crc32(n), sum(1)

KEYWORDS

       checksum, cksum, crc, crc32, cyclic redundancy check, data integrity, security, sum

COPYRIGHT

       Copyright (c) 2002, Pat Thoyts <patthoyts@users.sourceforge.net>

crc								       1.1.0								    sum(n)
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