shebanger
shebanger is a small CLI tool to transform a boring shell script into an
exciting series of shebang lines!
shebanger takes a shell script as input, and outputs a series of shell
scripts. Each of the output shell scripts only consists of a shebang line, they
don't have any code in their body. Executing the first output shell script will
run your original input shell program.
Installation
This section lists installation instructions for various Linux distros.
Generic Linux
There is a statically-linked x86_64 Linux ELF binary for shebanger available on each of
the GitHub Releases.
Nix / NixOS
Cloudy can be built with Nix by using the .nix files in this repo:
$ nix-build
You can find the shebanger binary in ./result/bin/shebanger.
You can also install shebanger from Nixpkgs by using the haskellPackages.shebanger
derivation:
$ nix-build '<nixpkgs>' -A haskellPackages.shebanger
Other Distros
PRs are welcome adding instructions for installing Cloudy on other Linux
distributions!
Usage
shebanger assumes it will be available on your PATH. You might see errors
with the following commands if shebanger can't be found on your PATH.
There is an example shell script to use with shebanger in this repo called
test.sh:
$ cat test.sh
#!/usr/bin/env bash
echo "arguments to this script: $@"
...
First, run shebanger on this script:
$ shebanger ./test.sh
This outputs a bunch of scripts named like the following:
$ ls test.sh.shebanged*
test.sh.shebanged
test.sh.shebanged.1
test.sh.shebanged.2
test.sh.shebanged.3
test.sh.shebanged.4
test.sh.shebanged.5
...
Each of these scripts is just a single line, and they look like the following:
$ cat ./test.sh.shebanged
#!/usr/bin/env -S shebanger exec IyEvdXNyL2Jpbi9lbnYgYmFzaAoKZWNobyAiYXJndW1lbnRzIHRvIHRoaXMgc2NyaXA=
You can see that this is a script that only consists of a shebang line. The
contents of the original script are split into 50-byte chunks, base-64 encoded,
passed within the shebang lines of the output scripts.
If you run ./test.sh.shebanged, the original test.sh will be reconstructed
and executed:
$ ./test.sh.shebanged hello this is an argument
arguments to this script: hello this is an argument
...
How Does shebanger Work?
shebanger works by base-64-encoding the original input script, and splitting
it up into the shebang lines of a series of output scripts. Each of these
output scripts consist of only a shebang line.
When running the output script, by executing each output script one-by-one in
turn, shebanger collects the contents of the original script, reconstructs
it, and executes it.
shebanger actually doesn't require the input to be a script, it works on any
executable. However, see the following sections on limitations of this.
Limitations
Currently shebanger collects the contents of the original scripts into an
environment variable, and passes that along when exec'ing the next script.
This means that shebanger is not able to execute scripts longer than a few
hundred kilobytes, since they tend to overflow the max size of all environment
variables.
Inspiration
shebanger is inspired by bangscript
by @viperML. The About explanation of bangscript is:
Embed scripts in a shebang
When I read this, I immediately thought it would be what shebanger currently
is. Since bangscript is instead something actually useful, I knew I needed to write
shebanger.
FAQs
-
Q: Why would someone ever actually use shebanger?
A: ...