I've been looking for standards on "correct" variable scope in ksh but
the IEEE Std 1003.1-2008 stuff on the Open Group site doesn't mention
any rules?
http://www.opengroup.org/onlinepubs/9699919799/utilities/contents.html
I found an interesting behavior in our ksh (pdksh) implementation, and
I'd like to know if the behavior is considered correct?
When you append to a variable within a 'for' loop, the changes are
exist after the loop ends, but if you do the same within a 'while'
loop, the changes are lost?
Example Code:
********************************************************************
#!/bin/ksh
# Test Setup
mkdir testdir
cd testdir
touch f00.txt f01.txt f02.txt
ls -1 f0?.txt >list.txt
# $ cat flist.txt
# f00.txt
# f01.txt
# f02.txt
# Set the Internal Field Separator to newline.
IFS='
';
# Append space separated list elements to a variable inside a for loop.
printf "\n\nTesting 'for' Loop\n";
for FNAME in `cat list.txt`; do
if [[ -z $FLIST ]]; then
FLIST="$FNAME";
else
FLIST="$FLIST $FNAME";
fi;
printf "FLIST: %s\n" "$FLIST";
done;
# Reset the Internal Field Separator to space (default).
IFS=' ';
# Print out all list elements in the variable.
printf "\n*** List From 'for' Loop ***\n";
for FNAME in $FLIST; do
printf "FILE_LIST_ELEMENT: %s\n" "$FNAME";
done;
printf "\n\nTesting 'while' Loop\n";
# Now we try the same type of thing with the 'while' loop.
cat list.txt | while read -r WNAME; do
if [[ -z $WLIST ]]; then
WLIST="$WNAME";
else
WLIST="$WLIST $WNAME";
fi
printf "WLIST: %s\n" "$WLIST";
done
# Print out all list elements in the variable.
printf "\n*** List From 'while' Loop ***\n";
for WNAME in $WLIST; do
printf "FILE_LIST_ELEMENT: %s\n" "$WNAME";
done
exit 0
********************************************************************
With both the 'for' and the 'while' loops, when the loop is running
the changes made to the variable are available, but once you leave the
scope of the loop (do,done), the behavior of variables modified within
the two types of loops differ.
I realize the IEEE/POSIX standard was based on ksh93, and our pdksh is
only partially compliant with ksh93, but I'm wondering if the "correct"
behavior for variable scope is formally standardized and/or documented
anywhere?
--
J.C. Roberts
