CODEWITHSUNDEEP
bash
Pradeep Gupta
Pradeep Gupta

Reputation: 407

Want to echo good error message in case of linux command failed

I am trying to write a function in bash so that when any command fails, It will print a nice error message, I tried this

#!/bin/bash
msg()
{
  if echo $? > 0 ; then
    echo "==> Something wrong happened. Please see /var/log/install.log"
  else
    echo "==> Done"
  fi
}

But when I tried to use them in this way:

#!/bin/bash
msg()
{
  if echo $? > 0 ; then
    echo "==> Something wrong happened. Please see /var/log/install.log"
  else
    echo "==> Done"
  fi
}

mkdir vcvcxvcxv
msg

Then I ran this on terminal

$ bash check 
mkdir: vcvcxvcxv: File exists
==> Something wrong happened, Please see /var/log/install.log

I got same output whatever. But I suppose to get the "Done" message when my command succeeds. Is there any help in this regard?

Upvotes: 0

Views: 777

Answers (2)

tripleee
tripleee

Reputation: 189377

Although you got your immediate problem fixed already, your code isn't very idiomatic, and violates some fundamental shell scripting principles.

  • Errors should produce an error status
  • Error messages should go to standard error
  • Don't be needlessly verbose

So the simplest fix is really

mkdir vcvcxvcxv || exit

since mkdir already produces an error message on stderr, and exit will propagate the value of $? to the calling process.

Incidentally, you can get much the same effect with set -e but it is slightly cumbersome to use for the newcomer.

If you want the "helpful" error message, perhaps this;

death () {
    rc=$?
    echo "$0: see /var/log/install.log" >&2
    exit $rc
}

mkdir vcvcxvcxv || death
echo "$0: done." >&2

would be closer to what you really need. Notice how the status messages are redirected to standard error (and each has the name of the script, so you can see what's causing the failure when you have scripts calling scripts calling scripts, etc) and the exit status is naturally propagated to the caller, and the entire script aborted, in the case of a fatal error. Also, the flow of the main script becomes more natural as it grows;

something || death
additional thing || death
final thing || death
echo "$0: done." >&2

(Of course, if failure means death always, you actually want set -e.)

Upvotes: 1

Ignacio Vazquez-Abrams
Ignacio Vazquez-Abrams

Reputation: 798606

This:

if echo $? > 0

does not do anything you want it to.

if [ $? -ne 0 ]

Upvotes: 3

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