In article <Z6m1h.6506$Wy6.4104@trnddc01>,
"Peter" <peter@localhost.com> wrote:

> I was reviewing the Suse/Gentoo run-crons script, and comparing it with
> some elementary scripts I had written. All of a sudden, I realized that
> despite reading the docs and advanced scripting manual, I really did not
> have a good grasp on the concept of when to quote, enclose in a brace, etc.
>
> This snippet crystallizes my confusion. As written, the variable
> definition for LOCKFILE uses braces, but I found that it made no
> difference whether or not I used braces, quotes, or any combination. I
> understand that certain test contructs, such as [ -n... ] require quotes,
> and if I want to manipulate a variable, braces are useful for
> substitution, but could someone please explain if the first assignment of
> LOCKFILE is proper, and why? For that matter, when would the assignment to
> LOCKDIR have to be quoted? If there is a whitespace?
>
> Thanks a lot!
>
> #!/bin/sh
>
> LOCKDIR=/var/spool/cron/lastrun
> LOCKFILE=${LOCKDIR}/lock
>
> echo "braces no quotes $LOCKFILE"
>
> LOCKFILE="${LOCKDIR}"/lock
> echo "braces quote $LOCKFILE"
>
> LOCKFILE=$LOCKDIR/lock
> echo "no braces no quote $LOCKFILE"
>
> LOCKFILE="$LOCKDIR"/lock
> echo "no braces quote $LOCKFILE"

None of the above examples need the braces or quotes. But here are some
examples where they're necessary:

LOCKFILE=${LOCKDIR}1/lock

Without the braces, it would look for a variable named LOCKDIR1.

LOCKFILE="$LOCKDIR/lock file with spaces"

Without the quotes, it would set the environment variable to
$LOCKDIR/lock while trying to execute the command line "file with
spaces".

STRINGWITHSPACES="foo bar"
echo $STRINGWITHSPACES
echo "$STRINGWITHSPACES"

The first one loses the multiple spaces between the words.

However, you don't need it here:

OTHERSTRING=$STRINGWITHSPACES

because word splitting of the assignment portion of a command is done
before variable expansion.

--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
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