Difference Between #!/usr/bin/bash and #!/usr/bin/env bash

In this article, we are going to see that what is the difference between #!/usr/bin/bash and #!/usr/bin/env bash

What is #!? 

This is called the shebang character sequence consisting of the character’s number sign and an exclamation mark at the beginning of the script. It is also called sharp-exclamation, sha-bang, hashbang, pound-bang, or hash-piling. this character sequence tells the OS to invoke the specified shell to execute the commands that follow in the script. 

Using #!/usr/bin/bash

This is a shebang line used in script files to set bash, present in the “/bin” directory, as the default shell to execute the commands in the file. It defines the absolute path /usr/bin/bash to the Bash shell.

We can find where your bash is located in the system by which command:

$ which bash
/usr/bin/bash

using  #!/usr/bin/bash is recommended when users want to accurately point to an interpreter’s absolute path. it also offers high security and is open to passing additional parameters.

#!/usr/bin/bash -r

Using #!/usr/bin/env bash

It is also a shebang line used in script files to execute commands with a bash shell. the difference is it uses the env command to display the environment variable present in the system, then executes commands with a defined interpreter. The env command works by instructing the system to look for specifies interpreters through the $PATH variable and use the first occurrence found.

$ which bash
/usr/bin/env

Also, you can identify all the current environment variables defined by the shell by using the command env.

$ env

$ env | grep PATH

 Table of Difference Between #!/usr/bin/bash and #!/usr/bin/env bash

From the above, we can see $PATH contains symlinks to /bin and other directories also.

Sr.No	#!/usr/bin/bash	#!/usr/bin/env bash
1	It offers more security	It offers more Portability
2	It can support extra parameters passing after the declaration of an interpreter.	Automatically searches for the interpreter and chooses the first occurrence.
3	More specifically, since we are declaring the exact path to an interpreter.	Cannot support extra parameter passing because the system reads them as a single command.
4	Not offers modification to the environment.	Offer the possibility to modify the environment of the invoked command
5	Runs the only bash executable that is located in #!/usr/bin/bash.	It makes sure that if the script interpreter is accessible on the path then it will be found and gets executed.