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Full Discussion: While read
Top Forums Shell Programming and Scripting While read Post 303014120 by Scott on Monday 5th of March 2018 12:31:33 PM
Old 03-05-2018
Quote:
Originally Posted by Yoda
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

Being a Korn shell user, myself, I often overlook the pipe / sub-shell thing in Bash.. it's good that you pointed that out to the OP Smilie
 

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sum(1B) 					     SunOS/BSD Compatibility Package Commands						   sum(1B)

NAME
sum - calculate a checksum for a file SYNOPSIS
/usr/ucb/sum file... DESCRIPTION
sum calculates and displays a 16-bit checksum for the named file and displays the size of the file in kilobytes. It is typically used to look for bad spots, or to validate a file communicated over some transmission line. The checksum is calculated by an algorithm which may yield different results on machines with 16-bit ints and machines with 32-bit ints, so it cannot always be used to validate that a file has been transferred between machines with different-sized ints. 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). ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWscpu | +-----------------------------+-----------------------------+ SEE ALSO
sum(1), wc(1), attributes(5), largefile(5) DIAGNOSTICS
Read error is indistinguishable from EOF on most devices; check the block count. NOTES
sum and /usr/bin/sum (see sum(1)) return different checksums. This utility is obsolete. SunOS 5.10 8 Nov 1995 sum(1B)
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