What is the preferred Bash shebang

Question

Is there any Bash shebang objectively better than the others for most uses       usr bin env bash    bin bash    bin sh    bin sh - etc   I vaguely recall a long time ago hearing that adding a dash to the end prevents someone passing a command to your script  but can   t find any details on that

User · Answer

Using a shebang line to invoke the appropriate interpreter is not just for BASH. You can use the shebang for any interpreted language on your system such as Perl, Python, PHP (CLI) and many others. By the way, the shebang

#!/bin/sh -

(it can also be two dashes, i.e. --) ends bash options everything after will be treated as filenames and arguments.

Using the env command makes your script portable and allows you to setup custom environments for your script hence portable scripts should use

#!/usr/bin/env bash

Or for whatever the language such as for Perl

#!/usr/bin/env perl

Be sure to look at the man pages for bash:

man bash

and env:

man env

Note: On Debian and Debian-based systems, like Ubuntu, sh is linked to dash not bash. As all system scripts use sh. This allows bash to grow and the system to stay stable, according to Debian.

Also, to keep invocation *nix like I never use file extensions on shebang invoked scripts, as you cannot omit the extension on invocation on executables as you can on Windows. The file command can identify it as a script.

User · Answer

bin sh is usually a link to the system s default shell  which is often bash but on  e g   Debian systems is the lighter weight dash   Either way  the original Bourne shell is sh  so if your script uses some bash  2nd generation   Bourne Again sh   specific features        tests  arrays  various sugary things  etc    then you should be more specific and use the later  This way  on systems where bash is not installed  your script won t run  I understand there may be an exciting trilogy of films about this evolution   but that could be hearsay   Also note that when evoked as sh  bash to some extent behaves as POSIX standard sh  see also the GNU docs about this

User · Answer

It really depends on how you write your bash scripts  If your  bin sh is symlinked to bash  when bash is invoked as sh  some features are unavailable   If you want bash-specific  non-POSIX features  use    bin bash

User · Answer

bin sh as most scripts do not need specific bash feature and should be written for sh  Also  this makes scripts work on the BSDs  which do not have bash per default

User · Answer

You should use    usr bin env bash for portability  different  nixes put bash in different places  and using  usr bin env is a workaround to run the first bash found on the PATH  And sh is not bash

User · Answer

I recommend using      bin bash   It s not 100  portable  some systems place bash in a location other than  bin   but the fact that a lot of existing scripts use    bin bash pressures various operating systems to make  bin bash at least a symlink to the main location   The alternative of      usr bin env bash   has been suggested -- but there s no guarantee that the env command is in  usr bin  and I ve used systems where it isn t   Furthermore  this form will use the first instance of bash in the current users  PATH  which might not be a suitable version of the bash shell    But  usr bin env should work on any reasonably modern system  either because env is in  usr bin or because the system does something to make it work  The system I referred to above was SunOS 4  which I probably haven t used in about 25 years    If you need a script to run on a system that doesn t have  bin bash  you can modify the script to point to the correct location  that s admittedly inconvenient    I ve discussed the tradeoffs in greater depth in my answer to this question   A somewhat obscure update  One system I use  Termux  a desktop-Linux-like layer that runs under Android  doesn t have  bin bash  bash is  data data com termux files usr bin bash  -- but it has special handling to support    bin bash

[bash] What is the preferred Bash shebang?

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