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!

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. — Miguel Roque, May 29 '14 at 07:42

score 53 · Answer 1 · edited Jun 28 '18 at 10:43

53

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 `&'"

edited Jun 28 '18 at 10:43

peter_v

103

answered May 29 '14 at 07:42

Nidal

8,956

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. – Miguel Roque May 29 '14 at 07:45
1

@MiguelRoque see updates – Nidal May 29 '14 at 07:46
1

I tried putting the output inside a HEREDOC and it worked also. Thanks a lot @Networker! – Miguel Roque May 29 '14 at 07:52
1

Someone reverted the edit I did, because I had a "syntax error near &" and removed the space after >. A justification would have been nice. – Pierre.Sassoulas Jan 12 '18 at 10:08
I tried to edit because : Make sure to use 2>&1 and not 2> &1 to avoid the error "syntax error near unexpected token `&'" – peter_v Jun 28 '18 at 08:14

graphite · Answer 2 · 2014-05-29T08:06:18.293

19

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

edited May 29 '14 at 08:06

answered May 29 '14 at 07:47

graphite

501

1

Always use $(command) instead of backticks for command substitution. It is better :) – Sreeraj Feb 13 '15 at 07:02
I know it is better (I've had less issues using $()), but why is that? – KolonUK Oct 29 '19 at 11:48
@KolonUK For one thing, you can nest them. – Nobody May 21 '20 at 14:05

score 10 · Answer 3 · edited Feb 08 '19 at 11:49

10

To return the error message in a variable, simply;

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

echo $error

edited Feb 08 '19 at 11:49

Prvt_Yadav

5,882

answered Feb 08 '19 at 10:56

Henry

200

2

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. – R. W. Prado Sep 15 '21 at 20:48

score 6 · Answer 4 · answered Nov 04 '17 at 10:58

6

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
$

answered Nov 04 '17 at 10:58

BurningKrome

238

harish.venkat · Answer 5 · 2014-05-29T07:52:44.790

4

To append to a file use /sbin/modprobe -n -v hfsplus 2>> filename

edited May 29 '14 at 07:52

answered May 29 '14 at 07:44

harish.venkat

7,573

score 4 · Answer 6 · answered Feb 13 '15 at 06:22

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

How to capture error message from executed command?

6 Answers6

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