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Top Forums Shell Programming and Scripting Advanced error handling in shell scripts Post 302363695 by script_man on Wednesday 21st of October 2009 05:10:53 AM
Old 10-21-2009
Advanced error handling in shell scripts

Hi all


I've got a question regarding error handling in shell scripts. My background is mainly object oriented programming languages, but for a year or so I've been doing more and more (bash) shell scripting (which I quite enjoy by the way).

To handle errors in my scripts I often find myself doing something like:

Code:
<execute some command>
  if [ $? -ne 0 ] ;then
    <handle error>
  fi

In many cases the <handle error> is the same for the commands executed, so you end up duplicating code. Thus I think it would be better to encapsulate this code in a function, e.g.

Code:
exec_cmd()
  {
    $1 # the command to be executed is passed in as an argument
    if [ $? -ne 0 ] ; then
      <handle error>
    fi
  }

And execute commands by calling this function:
Code:
exec_cmd "<some command>"

Furthermore, the function can easily be enhanced to write the command as well as the command output and return code to a log file:
Code:
exec_cmd()
{
  echo ""   >> $log_file
  echo "---------------------------------------------------------" >> $log_file
  echo "$1" >> $log_file
  $1        >> $log_file 2>&1
  return_code=$?
  if [ $return_code -ne 0 ] ; then
    echo "ERROR - $1 failed with $return_code"
    exit 1
  fi
}

exec_cmd "<cmd1>"
exec_cmd "<cmd2>"
exec_cmd "<cmd2>"
...

I found this quite handy to handle errors in my scripts. If you write command, output and return code to a log file, it also makes it quite easy to investigate problems with scripts that run in the background.


Now my question is:
How is that as a practise? Is it common? Or would it be considerd as bad and if so why? Has the bash already got something like this build in? (E.g. there might be an exit on fail option; I also know that you can start scripts with an option which outputs the commands which are being executed).

How do the experienced people here do the error handling in their scripts?

Thanks and best wishes
 

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RBASH(1)						      General Commands Manual							  RBASH(1)

NAME
rbash - restricted bash, see bash(1) RESTRICTED SHELL
If bash is started with the name rbash, or the -r option is supplied at invocation, the shell becomes restricted. A restricted shell is used to set up an environment more controlled than the standard shell. It behaves identically to bash with the exception that the follow- ing are disallowed or not performed: o changing directories with cd o setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV o specifying command names containing / o specifying a file name containing a / as an argument to the . builtin command o specifying a filename containing a slash as an argument to the -p option to the hash builtin command o importing function definitions from the shell environment at startup o parsing the value of SHELLOPTS from the shell environment at startup o redirecting output using the >, >|, <>, >&, &>, and >> redirection operators o using the exec builtin command to replace the shell with another command o adding or deleting builtin commands with the -f and -d options to the enable builtin command o using the enable builtin command to enable disabled shell builtins o specifying the -p option to the command builtin command o turning off restricted mode with set +r or set +o restricted. These restrictions are enforced after any startup files are read. When a command that is found to be a shell script is executed, rbash turns off any restrictions in the shell spawned to execute the script. SEE ALSO
bash(1) GNU Bash-4.0 2004 Apr 20 RBASH(1)
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