[Techtalk] Shell scripting for newbies

[Conor Daly]

On Thu, Feb 19, 2004 at 05:25:30PM -0800 or so it is rumoured hereabouts, 
Kai MacTane thought:
> 
> >url=$1; [ -z $url ] && url=about:blank
> 
> After the semicolon, we have a test (the part in square brackets). The 
> square brackets themselves tell bash to treat their contents as something 
> to be tested for truth or falsehood.

To be a bit pedantic on this, the first bracket '[' is a symlink to the
program 'test' which expects a ']' as its last argument when called as
'['.  You can also run 'test' in the same fashion with no closing ']'.
AIUI, the '[ .. ]' invocation was designed to look 'natural' in an
'if-then' clause thus:

if [ -z $url ]; then
....
fi

while the quoted construct above could be written:

test -z $url && url=about:blank

though it appears lately that people are using [...] instead which is a
little harder for a novice bash reader to understand.

Note than 'man [' gives 'No manual entry for [' while 'man test' gives the
manpage and all the switches!!

Conor
-- 
Conor Daly <conor.daly at oceanfree.net>

Domestic Sysadmin :-)
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