Linux Reader Access files and folders on Ext, UFS, HFS, ReiserFS, APFS file systems – from Windows
Linux Reader
Access files and folders on Ext, UFS, HFS, ReiserFS, APFS file systems – from Windows

How to use the /usr/bin/env command in a shell script

Here you will find out:

  • why you need to use the /usr/bin/env command
  • how to use ENV in a script
  • how to define the path for the ENV command
  • when DiskInternals can help you

Are you ready? Let's read!

Why you need to use the /usr/bin/env command

If you have noticed, all shell scripts usually start with this line:

While Perl scripts start with:

This first line is simply referred to as a shebang. Everything written on this line is very important for running your bash or Perl script. Typically, a UNIX system will read the interpreter defined on the first line of a script, be it bash or Perl. But, bash or Perl is not always on the same path as /bin/bash or /usr/bin/Perl. Thus, if you wish for your script to run across all UNIX-like OSes, you need to use the /usr/bin/env command as the shebang for your script.

Portability with #!/usr/bin/env

Using the ENV command, you can make your script run across UNIX-like systems without limitations. The command introduces a direction to call sh/bash/Perl.

Examples:

From the examples above, the ENV utility will invoke the first sh or bash executable found in the user's $PATH.

Another portability problem faced by most users is the interpretation of arguments. Normally, Linux and Cygwin systems do not split up arguments. For example:

From the command above, “python -c” is expected to run as one argument on /usr/bin/env.

How to use ENV in a script

The following is how you can use the ENV command in a script.

ENV works for different purposes, which include:

  • Printing all environment variables
  • Executing other commands in a custom environment
  • Modifying the value of variables
  • Adding or removing variables

How to define the path for the ENV command

Using TYPE or COMMAND, you can set a path ENV command:

Input:

Output:

Different *nix systems will print the following as the path for ENV command:

Examples of using ENV

Perl example:

Python 2.x example:

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