Once upon a time, Les Mikesell <lesmikesell@xxxxxxxxx> said:
> On Fri, Feb 13, 2015 at 11:54 PM, Always Learning <centos@xxxxxxxxxxx> wrote:
> >> 16 if [ $file = "law00css" ]
>
> You still missed the part about quoting variables. You quote plain
> strings to hold embedded spaces together (or single-quotes to avoid
> parsing metacharacters). You use double quotes around $variables so
> they don't disappear completely if the variable isn't set, causing a
> syntax error. To understand it completely you need to know the order
> of operations as the shell makes multiple passes over the line,
> parsing, processing metacharacters, and expanding variables. And I
> don't know where to find a concise description of that any more.
The thing to remember is that originally, the left square bracket [ was
an external command (an alias of the "test" command). The shell
interpreter just ran commands and tested the output. So, consider
everything past the "if" as a single command, and treat it accordingly
(so quoting arguments just like you would to "ls" or something).
So, in the above line, $file would be expanded by the shell as part of
command argument processing, and it is empty/not set, the command would
be run as:
[ = law00css ]
That's invalid syntax. If instead, you call it with $file in quotes:
[ "" = law00css ]
That's valid syntax (and then tests as false).
--
Chris Adams <linux@xxxxxxxxxxx>
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