Sbang lets you run scripts with long shebang lines

sbang

sbang lets you run scripts with very long shebang (#!) lines.

Many operating systems limit the length and number of possible arguments in shebang lines, making it hard to use interpreters that are deep in the directory hierarchy or require special arguments.

To use, put the long shebang on the second line of your script, and make sbang the interpreter, like this:

#!/bin/sh /path/to/sbang
#!/long/path/to/real/interpreter with arguments

sbang will run the real interpreter with the script as its argument.

Longer explanation

Suppose you have a script, long-shebang.sh, like this:

#!/very/long/path/to/some/interp

echo "success!"

If very/long/path is actually very long, running this script will result in an error on some OS's. On Linux, you get this:

$ ./long-shebang.sh
-bash: ./longshebang.sh: /very/long/path/to/some/interp: bad interpreter:
       No such file or directory

On macOS, the system simply assumes the interpreter is the shell and tries to run with it, which is not likely what you want.

sbang on the command line

You can use sbang in two ways. You can use it directly, from the command line, like this:

$ sbang ./long-shebang.sh
success!

sbang as the interpreter

You can also use sbang as the interpreter for your script. Put #!/bin/sh /path/to/sbang on line 1, and move the original shebang to line 2 of the script:

#!/bin/sh /path/to/sbang
#!/long/path/to/real/interpreter with arguments

echo "success!"

$ ./long-shebang.sh
success!

On Linux, you could shorten line 1 to #!/path/to/sbang, but other operating systems like Mac OS X require the interpreter to be a binary, so it's best to use sbang as an argument to /bin/sh. Obviously, for this to work, sbang needs to have a short enough path that it will run without hitting OS limits.

Other comment syntaxes

For Lua, node, and php scripts, the second line can't start with #!, as # is not the comment character in these languages (though they all ignore #! on the first line of a script). Instrument such scripts like this, using --, //, or <?php ... ?> instead of # on the second line, e.g.:

#!/bin/sh /path/to/sbang
--!/long/path/to/lua with arguments
print "success!"

#!/bin/sh /path/to/sbang
//!/long/path/to/node with arguments
print "success!"

#!/bin/sh /path/to/sbang
<?php #/long/path/to/php with arguments ?>
<?php echo "success!\n"; ?>

How it works

sbang is a very simple posix shell script. It looks at the first two lines of a script argument and runs the last line starting with #!, with the script as an argument. It also forwards arguments.

Authors

sbang was created by Todd Gamblin, tgamblin@llnl.gov, as part of Spack.

Related projects

The long-shebang project is like sbang but written in C instead of POSIX sh. It grew out of Nix a few months after sbang grew out of Spack, for similar reasons.

License

sbang is distributed under the terms of both the MIT license and the Apache License (Version 2.0). Users may choose either license, at their option.

All new contributions must be made under both the MIT and Apache-2.0 licenses.

See LICENSE-MIT, LICENSE-APACHE, COPYRIGHT, and NOTICE for details.

SPDX-License-Identifier: (Apache-2.0 OR MIT)

LLNL-CODE-811652

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