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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

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sum(1)								   User Commands							    sum(1)

NAME
sum - print checksum and block count for a file SYNOPSIS
sum [-r] [file...] DESCRIPTION
The sum utility calculates and prints a 16-bit checksum for the named file and the number of 512-byte blocks in the file. It is typically used to look for bad spots, or to validate a file communicated over some transmission line. OPTIONS
The following options are supported: -r Use an alternate (machine-dependent) algorithm in computing the checksum. OPERANDS
The following operands are supported: file A path name of a file. If no files are named, the standard input is used. USAGE
See largefile(5) for the description of the behavior of sum when encountering files greater than or equal to 2 Gbyte ( 2**31 bytes). ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables that affect the execution of sum: LC_CTYPE, LC_MESSAGES, and NLSPATH. EXIT STATUS
The following exit values are returned. 0 Successful completion. >0 An error occurred. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | |Availability |SUNWesu | |CSI |enabled | +-----------------------------+-----------------------------+ SEE ALSO
cksum(1), sum(1B), wc(1), attributes(5), environ(5), largefile(5) DIAGNOSTICS
"Read error" is indistinguishable from end of file on most devices; check the block count. NOTES
Portable applications should use cksum(1). sum and usr/ucb/sum (see sum(1B)) return different checksums. SunOS 5.10 7 Nov 1995 sum(1)
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