redirection in a shell script?

[Trever Furnish]

Hopefully this will be a simple question for someone.

In the HP posix shell (man sh-posix), is it possible to set output redirection at the beginning of a script and have that redirection apply to all subsequent lines in the script?

For example, instead of this:

#!/bin/sh
line1 >>/my/log.file
line2 >>/my/log.file
line3 >>/my/log.file

...I'd like to do somethine like this:

#!/bin/sh >>/my/log.file
line1
line2
line3

That particular method doesn't work and I can't find another one that does either. This would *really* clean up my scripts a lot.

I know I could redirect the output for the script itself when I invoke it, but there's always the possibility that if the script exits abnormally I won't get output at all - which defeats the whole purpose.

In Perl I could accomplish this with a simple re-opening of the standard output filehandle like so (example taken from the perlfunc man page):

open(STDOUT, '>', "foo.out") || die "Can't redirect stdout";
open(STDERR, ">&STDOUT") || die "Can't dup stdout";

That would attach STDOUT for the current process to foo.out and then duplicate STDOUT as STDERR.

It seems like there *has* to be some way to do it in a shell language, but I'm missing it...

Help? If anyone needs clarification, just let me know.

[Paula J Frazer-Campbell]

Trevor

How about:-

script >> logfile

You will have to echo out each result.

Paula

[Sridhar Bhaskarla]

Hi Trever,

You can keep the commands in {} to combine the output. For ex., your script would do the following

#!/sbin/sh
...
...
{
line 1
line 2
line 3
} > /my/log.file


-Sri

[A. Clay Stephenson · Accepted solution]

You need to check out the 'exec' statement. Man sh_posix for details.

exec 1>/tmp/myfile
exec 2>>/tmp/myerrs

Stdout is redirected to /tmp/myfile
Stderr is redirected to /tmp/myerrs in append mode

[Deshpande Prashant]

Hi
I use following method.
##-----
#Define common variables ##
HP=`hostname`
LOGFILE=/home/system/LOGS/${HP}-Log

exec 2>&1 >>${LOGFILE}
## start commands

command1.
command2.
...

##-----

Thanks.
Prashant Deshpande.

[Duncan Edmonstone]

Hi,

use exec (see man sh-posix) :

---------------------------
#!/usr/bin/sh

exec 1>mylog

echo hello
echo more
exit
---------------------------


In the above, all stdout will go to mylog

HTH

Duncan

[Trever Furnish]

It figures - you ponder something forever, then the second you ask someone else to think about it you figure something out that works.

But this isn't very elegant at all, so I'd still love to hear it if there's a better way...

Here's the work-around I thought of: Run the script with another script as a wrapper - redirect the output of the internal script to a temporary file. When the internal script is done, then mail/archive/whatever the log file. This gets around a "broken pipe" losing data because the log file writes happen immediately rather than at the end of the process as pipes do.

Actually, I think I gave a bad example initially - instead of writing to a log file, I'm more worried about the case of losing data where I would normally be executing a sub-process and sending it to a pipe, as in this crontab entry example:

0 0 * * * (date; bdf) 2>&1 | /usr/bin/mail -s "bdf" foo@bar.com

[hpuxrox]

You could use a function to do this

#! /bin/sh

Function1 () {

command1
command2
commadn3
}

Function1 > file

[Trever Furnish]

Wow.

Access to the ITRC forums make HP's premium prices well worth it. :-) By the time I'd posted my second message in this article five of you had already replied.

Exec. And it's right there in the man page. Color me embarrassed. But also very grateful.

Many thanks to all. :-) I'll assign points shortly.

[harry d brown jr]

Trevor,

I myself just learned something new (exec 1>>file), I wonder if my boss will let me go home now....yeah right


live free or die
harry