CODEWITHSUNDEEP
bashshelloutput-redirect
Marcus Frenkel
Marcus Frenkel

Reputation: 711

In a bash shell, redirect standard error to standard output and reference the error part with a string prefix

The command od / /dev/null returns both standard error and standard output and is used here just for test.

I can redirect the standard error to standard output with:

echo "The command result is: $(od / /dev/null 2>&1)"

Which returns:

The command result is: od: /: read error: Is a directory
0000000

Whereas the error part is "od: /: read error: Is a directory" and the non error one is "0000000".

I need to add a reference in the output to distinguish which part is the standard error, by adding a prefix "The error is:", and get and output like:

The command result is: 0000000
The error is: od: /: read error: Is a directory

If there is no error, the string "The error is:" can still be part of the output.

Any advise how to accomplish this?

EDIT:

The answer from choroba works for the test command od / /dev/null, but when I try to use the following ssh command (which is what I'll actually use), the standard error goes at the end of the output instead of within the START/END strings and the START string is missing:

Command: echo "START___$(ssh [email protected] 2>&1 2> >(sed 's/^/ERR: /' >&2))___END"
Output: ___END__ERR: ssh: Could not resolve hostname 1.1.1.900: Name or service not known

When I use the test command with the addition of START/END strings, I get a normal output whereas the standard output and error is within START/END strings:

Command:echo "START___$(od / /dev/null 2>&1 2> >(sed 's/^/ERR: /' >&2))___END"
Output: START___0000000
ERR: od: /: read error: Is a directory___END

Any help for this scenario?

EDIT 2

I added the ssh command in a subprocess but still have the problem. Interestingly, it works OK for telnet.

SSH:

Command: echo "START___$((ssh [email protected]) 2>&1 2> >(sed 's/^/ERR: /' >&2))___END"

Output: ___END__ERR: ssh: Could not resolve hostname 1.1.1.900: Name or service not known

Telnet:

Command: echo "START___$((telnet 1.1.1.900) 2>&1 2> >(sed 's/^/ERR: /' >&2))___END"

Output: START___ERR: telnet: could not resolve 1.1.1.900/telnet: Name or service not known___END

EDIT 3 - SOLUTION

The solution to work with ssh command is to filter control chars from the ssh response before feeding sed:

echo "START___$(ssh [email protected] 2>&1 2> >(tr -d '[:cntrl:]' | sed 's/^/ERR: /' >&2))___END"

Upvotes: 0

Views: 117

Answers (2)

agc
agc

Reputation: 8406

For Debian based Linuxes, run apt install devscripts, and then try the annotate-output util.

annotate-output od / /dev/null

Output:

07:21:44 I: Started od / /dev/null
07:21:44 E: od: /: read error: Is a directory
07:21:44 O: 0000000
07:21:44 I: Finished with exitcode 1

Upvotes: 0

choroba
choroba

Reputation: 241858

You can use sed and the process substitution:

echo "The command result is: $(od / /dev/null 2>&1 2> >(sed 's/^/ERR: /' >&2))"

Upvotes: 1

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