Variable value inconsistency on BASH and CSH

Question

May God never give you the bane of working on Solaris. Now, I am trying to run this simple shell script:

#!/bin/sh

input="a
b
c"
data="123"

while read eachline
do      
   data="$data$eachline"
done <<  EOF
$(echo "$input")
EOF

echo "$data"
exit 0

On RHEL(BASH) I receive output as expected i.e "123abc", however, on Solaris I receive just "123".

After fair bit of googling, I realized that Solaris is forking a process for code inside the while loop and hence the variable's($data) value is not reflected on the outside of while loop.

Any hope to make this code compatible on both platforms would be greatly appreciated.

And oh yes, using a temp file for redirection would not be a very elegant solution :| .

Answer 1

Do you have a bash executable on the Solaris box ? I note you're referring to bash on RHEL, but your shell is set to #!/bin/sh (i.e. the vanilla Bourne shell).

Answer 2

Your script works fine on Mac OS X 10.5, which is certified Single Unix Specification version 3.

The behaviour of while in /bin/sh on Solaris is very strange. Can you provide the link where you found the forking issue?

A possible solution may be to use another shell, e.g., /bin/ksh.

---

Edit

The examples provided by your links don't show an issue with while but a normal behaviour of any shell. The basic construct of all of them is:

first_command | second_command_updating_variable

The fact that second_command_updating_variable is a while loop is not important. What is important is that the second command of the pipe is executed in a subshell and cannot modify variables of its parent shell.

Answer 3

How about this (please note backticks):

#!/bin/sh

input="a
b
c"
data="123"

z=`while read eachline
do      
   data="$data$eachline"
done <<  EOF
$(echo "$input")
EOF
echo $data
`
echo $z
exit 0

Answer 4

This code below solved my problem. I guess the key here was to echo the variable from within the subshell and ofcourse, not use the "here" document.

I have tested this code on CSH/BASH/KSH.

#!/bin/sh
input="a
b
c"

printf "$input" | { 
data="123"
while read eachline
do      
    data="$data$eachline"
done 
echo "$data"
}

exit 0

My heartfelt thanks to all who participated in this discussion.

Answer 5

Why execute a subshell in the here document?

while read eachline
do      
   data="$data$eachline"
done <<  EOF
$(echo "$input")
EOF

You could just interpolate:

while read eachline
do      
   data="$data$eachline"
done <<  EOF
$input
EOF

Or echo:

echo "$input" | while read eachline
do      
   data="$data$eachline"
done

Actually, when I tested these, they all worked on Solaris just fine for me, so I'm not sure why you had trouble.