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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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NPM-RUN-SCRIPT(1)														 NPM-RUN-SCRIPT(1)

NAME
npm-run-script - Run arbitrary package scripts SYNOPSIS
npm run-script <command> [--silent] [-- <args>...] alias: npm run DESCRIPTION
This runs an arbitrary command from a package's "scripts" object. If no "command" is provided, it will list the available scripts. run[-script] is used by the test, start, restart, and stop commands, but can be called directly, as well. When the scripts in the package are printed out, they're separated into lifecycle (test, start, restart) and directly-run scripts. As of ` https://blog.npmjs.org/post/98131109725/npm-2-0-0, you can use custom arguments when executing scripts. The special option -- is used by getopt https://goo.gl/KxMmtG to delimit the end of the options. npm will pass all the arguments after the -- directly to your script: npm run test -- --grep="pattern" The arguments will only be passed to the script specified after npm run and not to any pre or post script. The env script is a special built-in command that can be used to list environment variables that will be available to the script at run- time. If an "env" command is defined in your package, it will take precedence over the built-in. In addition to the shell's pre-existing PATH, npm run adds node_modules/.bin to the PATH provided to scripts. Any binaries provided by locally-installed dependencies can be used without the node_modules/.bin prefix. For example, if there is a devDependency on tap in your package, you should write: "scripts": {"test": "tap test/*.js"} instead of "scripts": {"test": "node_modules/.bin/tap test/*.js"} to run your tests. The actual shell your script is run within is platform dependent. By default, on Unix-like systems it is the /bin/sh command, on Windows it is the cmd.exe. The actual shell referred to by /bin/sh also depends on the system. As of ` https://github.com/npm/npm/releases/tag/v5.1.0 you can customize the shell with the script-shell configuration. Scripts are run from the root of the module, regardless of what your current working directory is when you call npm run. If you want your script to use different behavior based on what subdirectory you're in, you can use the INIT_CWD environment variable, which holds the full path you were in when you ran npm run. npm run sets the NODE environment variable to the node executable with which npm is executed. Also, if the --scripts-prepend-node-path is passed, the directory within which node resides is added to the PATH. If --scripts-prepend-node-path=auto is passed (which has been the default in npm v3), this is only performed when that node executable is not found in the PATH. If you try to run a script without having a node_modules directory and it fails, you will be given a warning to run npm install, just in case you've forgotten. You can use the --silent flag to prevent showing npm ERR! output on error. You can use the --if-present flag to avoid exiting with a non-zero exit code when the script is undefined. This lets you run potentially undefined scripts without breaking the execution chain. SEE ALSO
o npm help 7 scripts o npm help test o npm help start o npm help restart o npm help stop o npm help 7 config January 2019 NPM-RUN-SCRIPT(1)
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