Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!ptsfa!ames!sdcsvax!ucsdhub!hp-sdd!hplabs!hp-pcd!uoregon!omepd!littlei!ogcvax!schaefer
From: schaefer@ogcvax.UUCP (Barton E. Schaefer)
Newsgroups: comp.unix.wizards
Subject: Re: Csh/sh bug or feature?
Message-ID: <1532@ogcvax.UUCP>
Date: 14 Jan 88 19:41:41 GMT
References: <sdeggo.170>
Reply-To: schaefer@ogcvax.UUCP (Barton E. Schaefer)
Organization: Oregon Graduate Center, Beaverton, OR
Lines: 100

In article <sdeggo.170> dave@sdeggo.UUCP (David L. Smith) writes:
>I was playing around with csh the other day and noticed something rather
>interesting.
>
>For example (with csh), if foo contained:
>
>'this is * '
>
>(with the quotes and everything)

So far so good ...

>and I do:
>
>set foo=`cat foo`
>
>echo $foo returns:
>'this is (and here is the contents of the directory I was in when I did the
>set)
>
>if I then set noglob, and echo foo again, I get the same thing.

Assuming that the directory started with two files named "file1" and "file2"
(for example), I take it this means you did something like:

% cat > foo
'this is * '
^D
% set foo=`cat foo`
% echo $foo
'this is file1 file2 foo '
% set noglob
% echo $foo
'this is file1 file2 foo '

Try looking at the output of "set" (no arguments), which shows all variable
settings.  You will see that the * was expanded during execution of the
    set foo=`cat foo`
command.  By the time you are doing the second echo there is no * to be
globbed.

% set
noglob
foo	('this is file1 file2 foo ')

(Other variable settings omitted for clarity.)  Note the parentheses around the
value of "foo".  This means that the value is a WORDLIST, not a single word.

% echo $#foo
6

The 6 words in the word list are:
    (1) 'this
    (2) is
    (3) file1
    (4) file2
    (5) foo
    (6) '

Note that the single quotes (') are treated as "ordinary" characters,
and the `` substitution causes the result of the command to be broken into
words at spaces, tabs, and newlines.  If you don't want this to happen, you
should do:

% set foo="`cat foo`"

(Note the double quotes outside the back quotes.)  This prevents breaking into
words at spaces and tabs, but newlines still cause breaks.  The double quotes
also prevent filename substitution from affecting the result of the ``.

>It
>seems as if it would be beneficial for the output to be directly substituted 
>for the `` string and be subject to the same rules as if it had been in the 
>file all along. 

When you consider that `` can be used to execute almost ANY command (careful
of those that produce LOTS of output!), not just "cat" of a file, you can see
why you might want filename substitution on the output.  However, the reason
that this happens comes from the order that the csh does its substitutions:
    (1) History substitution		!
    (2) Quotations			" and '
    (3) Alias substitution
    (4) Variable substitution		$ and colon modifiers
    (5) Command substitution		`
    (6) Filename substitution		[] ? and *
Note that quotations are looked for BEFORE command substitution, but that
filenames are not expanded until AFTER command substitution.  That's why the
quotes in the file do not protect the * from being expanded.

>David L. Smith
>Sinners can repent, but stupid is forever.

Well, then, we'll give you the benefit of the doubt and say that you "sinned"
by not reading the csh manual ....

-- 
Bart Schaefer			CSNET:	schaefer@cse.ogc.edu
				UUCP:	...{tektronix,verdix}!ogcvax!schaefer
"A band of BIG, DUMB, LOUDMOUTHED, BUNGLING OGRES is a GREAT ASSET to the
neighbohood.  It keeps out the RIFF-RAFF."		-- Wormy