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.
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:
Different *nix systems will print the following as the path for ENV command:
Examples of using ENV
Python 2.x example:
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