Once upon a time, Les Mikesell lesmikesell@gmail.com said:
On Fri, Feb 13, 2015 at 11:54 PM, Always Learning centos@u64.u22.net 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).