[plug] script error

[Craig Ringer]

Mr E_T wrote:
> On Thursday 12 January 2006 15:40, Jon Miller wrote:
> 
>>Any idea how to append 1 file to another?  using cat file1 >> file2 does not work in a script.
>>
> 

> also to get the perm right use 
> chmod --reference=${tmail}/{$1} ${cmail}/${1}
> chown --reference=${tmail}/{$1} ${cmail}/${1}

AFAIK permissions are only affected by the >> redirect operator if the 
second file must be created. In that case, I think the file is created 
according to the umask, so you would need to change the permissions if 
you need to override the defaults.

Usually, you're better off setting the umask at the beginning of the 
script. Please don't just write a hard-coded umask unless you REALLY 
know you need it; just set or clear the bits you absolutely need to 
control using the `&' and `|' binary operators.

I really hate it when programmers blindly set the `umask'. Not that I'm 
looking at you, Mozilla project, or anything...

> cat $omail/$1 > $cmail/$1
> cat $tmail/$1 >> $cmail/$1
> 
> Notice the first cat is a single > this creates or zreos the file first.

Strictly, it truncates it, creating it if it does not exist. It doesn't 
as such zero anything. If I have a 1MB file "spam" and run:

echo eggs > spam

this truncates `spam' to 5 bytes (4 bytes, plus newline because I didn't 
use `echo -n'). If `spam' didn't exist, it would've been created.

See:

$ info '(bash.info.gz)Redirections'

for details on this, and a lot of other important things. Another really 
good bash info page to read is:

$ info '(bash.info.gz)Shell Parameter Expansion'

This will teach you a LOT about smarter ways to manipulate the data you 
work with. You'll find it much less necessary to break out to `sed', 
`awk', or edit pipelines with `cut' and friends.

The bash manual isn't easy to find things in, can be rather dense, and 
isn't the best organized ... but it is very complete. Please don't 
ignore it.

--
Craig Ringer