How to capture error message from executed command?

Question

I was tasked to create an automated server hardening script and one thing that they need is a report of all the output of each command executed. I want to store the error message inside a string and append it in a text file.

Let's say I ran this command:

/sbin/modprobe -n -v hfsplus

The output of running this in my machine would be:

FATAL: Module hfsplus not found

How can I store that error message inside a string? Any help would be greatly appreciated. Thanks!

Solution 1

you can do it by redirecting errors command:

/sbin/modprobe -n -v hfsplus 2> fileName 

as a script

#!/bin/bash
errormessage=$( /sbin/modprobe -n -v hfsplus 2>&1)
echo $errormessage

or

 #!/bin/bash
errormessage=`/sbin/modprobe -n -v hfsplus 2>&1 `
echo $errormessage

if you want to append the error use >> instead of >

Make sure to use 2>&1 and not 2> &1 to avoid the error "syntax error near unexpected token `&'"

Solution 2

Simply to store as a string in bash script:

X=`/sbin/modprobe -n -v hfsplus 2>&1`
echo $X

This can be a bit better as you will see messages when command is executed:

TMP=$(mktemp)
/sbin/modprobe -n -v hfsplus 2>&1 | tee $TMP
OUTPUT=$(cat $TMP)
echo $OUTPUT
rm $TMP

Solution 3

I capture error like this

. ${file} 2>&1 | {
  read -d "\0" -t 0.01 error
    [ -z "$error" ] || log_warn Load completion ${file} failed: "\n${error}"
}

if source failed, I will capture the error and log it.log_warn is just a simple function.

BTW, I use this in my dotfiles

Solution 4

Newer bash versions (I.e. bash 4.1+):

$ msg=$(ls -la nofile 2>&1)
$ echo $msg
ls: cannot access nofile: No such file or directory
$ 

Solution 5

To return the error message in a variable, simply;

error=$(/sbin/modprobe -n -v hfsplus 2>&1 1>/dev/null)

echo $error

View more solutions

Comments

[JM S. Tubiera]

I tried running this command: var=$(/sbin/modprobe -n -v hfsplush) And then displaying it: $var But it still doesn't capture the error message inside the string.

[JM S. Tubiera]

I've tried that approach and it stores it DIRECTLY in the text file. I want it to store inside a string first so I can format the contents easily.

[JM S. Tubiera]

I tried putting the output inside a HEREDOC and it worked also. Thanks a lot @Networker!

[Sreeraj]

Always use $(command) instead of backticks for command substitution. It is better :)

[peter_v]

I tried to edit because : Make sure to use 2>&1 and not 2> &1 to avoid the error "syntax error near unexpected token `&'"

[KolonUK]

I know it is better (I've had less issues using $()), but why is that?

[Nobody]

@KolonUK For one thing, you can nest them.

[R. W. Prado]

That's the answer, since the other ones would append standard output to the variable. Usually, you want to know if the message comes from a error or not and that's perfect. For example, to throw a warning or to handle a bad situation in a script.