On Mon, Jan 16, 2012 at 09:25:30PM +0100, Andre Speelmans wrote:
> I was not trying, the OP had a script that did a:
> cat file | while read line; do something done
>
> Matthew commented that you should not rely on cat for reading a file
> line by line and I was curious as to why not. ...
I'm not aware of any particular reason not to use 'cat', and while it
doesn't cost a lot, it's usually less expensive to use redirection.
I just wanted to remind people that another way to redirect input (and
output) is through the exec command. For instance:
exec 0</usr/tmp/foo
exec 1>/usr/tmp/bar
exec 2>/usr/tmp/error
while read INLINE
do
echo $INLINE
done
would read lines from file "/usr/tmp/foo" and output them to
"/usr/tmp/bar", all within the shell. Moreover, any errors (should be none
with something this simple, of course) would go to "/usr/tmp/error" as
STDOUT.
But wait! There's more!
You can redirect to/from any numeric file descriptor. For instance:
exec 3</usr/tmp/foo
while read INLINE <&3
do
echo $INLINE
done
would open file descriptor 3 on "/usr/tmp/foo", and the "while read" will
walk through that file line by line.
You can close descriptors in a script when done with them, e.g.,
exec 3>&-
would close that descriptor opened in the above script snippet.
Cheers,
--
Dave Ihnat
dih...@dminet.com
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