Echo to StdErr

[Seth Hollist]

How could I use and echo or print statement from within a shell script to send information to Standard Error instead of Standard Out?

Thanks.

[Sridhar Bhaskarla]

Seth,

How about

echo "your_message" 1>&2

-Sri

[linuxfan]

Hi Seth,

By default both STDOUT and STDERR are displayed on your terminal.

Within a script if you want to send the display of STDOUT to STDERR you could do something like

echo "message" 2>err_log 1>&2

where your STDERR is being sent to err_log and you are forcing STDOUT to be redirected to STDERR (which is basically err_log)

-HTH
Ramesh

[Sridhar Bhaskarla]

Ramesh,

Just curious - what's the difference in the outputs of the conventional of redirection like

echo "my process" > errlog 2>&1

and the one you stated?

I am very much interested to know the case where Seth wanted to use stdErr.

-Sri

[linuxfan]

Hi Sridhar,

Actually AFAIK if you redirect STDOUT and STDERR to the same file, then it doesn't matter if you are using 2>&1 or 1>&2

Also I don't believe there is any difference in
echo "messages" > error.log 2>&1 and
ehco "messages" 2>error.log 1>&2

Since both the STDOUT and STDERR are getting redirected to the same file(error.log).

The only reason i specified 2>error_log is because sometimes i want STDOUT and STDERR to go to different files.

-Regards
Ramesh

[Seth Hollist]

The idea is to send STDOUT to a file and to send STDERR to the terminal or display.

echo my_message 1>&2 seems to work fine for what I wanted, but it would be better if I could prevent it from going to STDOUT as to keep it from wrighting to the log file as well.

[Sridhar Bhaskarla]

In fact, it doesn't really matter Seth. By default StdOut and StdErr will send the output to the terminal.

So, it is just the same if you do
echo "message" 2>&1 or simply
echo "message".

After understanding your task, I feel you can do this way.

some_commands > /tmp/yourlogfile

You are deliberately not specifying the StdErr redirection here so it will by default output to the terminal. However, the StdOut will go to yourlogfile.

What do you say?

-Sri

[linuxfan]

Hi Seth,

If you do
echo "messages" 1>&2
both STDOUT and STDERR will be displayed on your screen

echo "messages" 2>error_log
will display STDOUT to screen and STDERR to the error_log file

echo "messages" >error_log
will display STDERR to the screen and STDOUT to the error_log file

echo "messages" >error_log 2>&1
will redirect both STDOUT and STDERR to the file error_log

-HTH
Ramesh

[Seth Hollist]

I guess I should be more specific...

I've got a program that populates files with certain information. Within that program it calles another script

Other_script > log_file

Within the other script I have

echo my_message 1>&2

That way I see my_message as if it were eched to the terminal from the original scrip, even though it's comeing from the Other_scrip and getting into the log file as well.

[S.C. Fun]

Hi seth,
From the above, I perceived this is what u mean:
1.The script Other_script will produce stderr.
2.You need to redirect this stderr to log_file.
3.You also want to see this stderr on terminal when u run the script containing Other_script.
4.Stdout will go to log_file and terminal.

If the above is correct, then try this in your script:

other_script 2>&1|tee log_file

Rgds,
S.C. Fun

[Alan Riggs · Accepted solution]

If you script in posix or ksh then use the print command instead of echo. It has a number of useful features, among them the -u flag which allows you to specify which file descriptor (I/O stream) you wish to print to. Since STDERR is defined as descriptor 2, simply use:

print -u 2 "whatever"

[Seth Hollist]

S.C. Fun,

> 1.The script Other_script will produce stderr.

- Yes, That's bascially my whole question right there, how to make the script produce stderr.

> 2.You need to redirect this stderr to log_file.

- No, I'm already redirecting stdout to log_file. I don't need anything else going to the log_file, but I do want to be able to send other messages to the terminal through the use of stderr.

> 3.You also want to see this stderr on terminal when u run the script containing Other_script.

- Yes, stderr needs to only go to the termial.

> 4.Stdout will go to log_file and terminal.

- No... Stdout and only Stdout will go to the log_file.

[Joseph C. Denman]

WOW!! I'm still confused ***as always***

example, if you have a script.

#/sbin/sh #test.sh
echo "This is a test" >&2
##end of script

then run it as:

./test.sh > log_file

-This is a test- will be appear on the terminal, but will not go to the log_file. Only standard out will go to log_file. Is this what you are asking?


...jcd...

[Seth Hollist]

Yeah, something like that, except that

echo "This is a test" >&2

will still send something to the log file because all your doing is telling stdout to also go to stderr.

The fallowing answered my question and works great. Thanks.

print -u 2 "whatever"