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Bash Scripting: Echo to Standard Error

Hi all.

I'm trying to print out all arguments passed to a script on a single line sent to STDERR

My script:

#!/bin/bash
echo $* >&2

Am I missing something? I know that >&2 should send STDERR to whatever is after it, but do I need to specify that the line is an error or something?

Thanks

Try

Code:

#!/bin/bash

echo "$*" >&2

Hope this helps!

old but I thought I would make a correction

Code:

#!/bin/bash

echo $* 1>&2

$ cat myscript.sh
#!/bin/bash
# not sure how portable this is, but it works on rhel 5.4

echo "$*" >/dev/stderr

$ ./myscript.sh unix is fun
unix is fun
$ ./myscript.sh unix is fun 2>~/testing_dev_stderr
$
$ cat ~/testing_dev_stderr
unix is fun

OR

$ cat myscript.sh
#!/bin/bash
# perhaps a more portable way

echo "$*" >/dev/fd/2

$ ./myscript.sh unix is fun
unix is fun
$ ./myscript.sh unix is fun 2>~/testing_dev_stderr
$
$ cat ~/testing_dev_stderr
unix is fun

I suppose the bottom line is that STDERR should be
available to you in the form of a file ( like just about everything else in unix/linux )

Code:

#output to stdout aka chan 1

# 2 methods: NB default is stdout (chan 1) anyway ...

echo A 

echo A >1



# output to stderr aka chan 2

echo B >2



# output to both

# 2>&1 => output stderr (chan 2)to same chan (&) as stdout (chan 1)

echo C >1 2>&1

echo C 2>&1



# chan 0 is stdin

I realize this is an old post, but I recently needed this information so I'm posting here for people searching for this in the future.

Quote:

Originally Posted by chrism01 (Post 4412310)

Code:

#output to stdout aka chan 1

# 2 methods: NB default is stdout (chan 1) anyway ...

echo A 

echo A >1



# output to stderr aka chan 2

echo B >2



# output to both

# 2>&1 => output stderr (chan 2)to same chan (&) as stdout (chan 1)

echo C >1 2>&1

echo C 2>&1



# chan 0 is stdin

For me, this didn't work:

Code:

echo A >1

echo B >2

What happens for me is the "echo A" is redirected to a file named "1", and the "echo B" is redirected to a file named "2".

After some research and experimentation, I found that this works:

Code:

[~]# cat ./myscript.sh



#!/bin/sh -u



echo "Message A: This to stdout or wherever '1>' redirects."

echo "Message B: This to stdout or wherever '1>' redirects.">&1

echo "Message C: This to stderr or wherever '2>' redirects.">/dev/stderr

echo "Message D: This to stderr or wherever '2>' redirects.">&2

So, running the script I get:

Code:

[~]# #### Discard stdout... only stderr displays

[~]# ./myscript.sh 1>/dev/null

Message C: This to stderr or wherever '2>' redirects.

Message D: This to stderr or wherever '2>' redirects.



[~]# #### Discard stderr... only stdout displays

[~]# ./r.sh 2>/dev/null

Message A: This to stdout or wherever '1>' redirects.

Message B: This to stdout or wherever '1>' redirects.



[~]# #### Discard both stdout and stderr... nothing displays

[~]# ./r.sh 1>/dev/null 2>/dev/null

[~]# ./r.sh 1>/dev/null 2>/dev/null

[~]# ./r.sh >/dev/null 2>&1

[~]#

You can't really test this from the shell command line, because any of these or similar commands will all output to the screen, so it looks like the redirection has no effect:

Code:

[~]# echo A

A

[~]# echo B>&1

B

[~]# echo C>&2

C

[~]# echo D 2>&1

D

[~]# echo E>/dev/stderr

E

[~]#

If you put those commands in a script and test it like the "./myscript.sh" example shown above, you should see if it will work for you.

Here is some information about my system:

Code:

[~]# uname -srvmpio

Linux 3.2.45 #4 SMP Wed May 15 19:43:53 CDT 2013 x86_64 x86_64 x86_64 GNU/Linux



[~]# ls /bin/sh /dev/stdout /dev/stderr

lrwxrwxrwx 1 root root  4 Jul 18 23:18 /bin/sh -> bash

lrwxrwxrwx 1 root root 15 Jun 29  2013 /dev/stderr -> /proc/self/fd/2

lrwxrwxrwx 1 root root 15 Jun 29  2013 /dev/stdout -> /proc/self/fd/1

The above posts are helpful. Thank you!

I've just been seaching for a way to echo to stderr without disturbing the normal output (stdout).
And finally I got here.

Here's my testing results:

Code:

$ cat ./stderr_example.sh 

#!/bin/bash



if [ -z "$1" ]; then

    echo "error '>&2': argument 1 is empty." >&2

    echo "error '>/dev/fd/2': argument 1 is empty." >/dev/fd/2

    echo "error '>/dev/stderr': argument 1 is empty." >/dev/stderr

    exit 1

fi



echo "argument 1 is \`$1'"

$ var1=$(./stderr_example.sh arg1)

$ echo "var1=[$var1]"

var1=[argument 1 is `arg1']

$ var1=$(./stderr_example.sh)

error '>&2': argument 1 is empty.

error '>/dev/fd/2': argument 1 is empty.

error '>/dev/stderr': argument 1 is empty.

$ echo "var1=[$var1]"

var1=[]

All of the above three forms of echoing messages to stderr meet my need.

Some of my system information:

Code:

$ uname -srvmpio

Linux 3.2.0-59-generic-pae #90-Ubuntu SMP Tue Jan 7 23:07:06 UTC 2014 i686 i686 i386 GNU/Linux



$ ls -lgo --time-style=iso /bin/sh /dev/stdout /dev/stderr

lrwxrwxrwx 1  4 12-28 22:26 /bin/sh -> bash

lrwxrwxrwx 1 15 03-03 21:12 /dev/stderr -> /proc/self/fd/2

lrwxrwxrwx 1 15 03-03 21:12 /dev/stdout -> /proc/self/fd/1