Writing linux scripts in C++

Concept

In short (for experienced linux users)

1. Compile and install build-n-run.cpp.

2. Create C++ source file, prepend it with shebang line #!/path/to/build-n-run, make it executable chmod +x script.cpp and run: ./script.cpp.

3. build-n-run compiles script.cpp to ~/bin/build-n-run.compiled/ only if source file is newer than compiled binary, and then runs compiled binary.

In detail

They say compiled languages are inconvenient for scripting because you have to recompile your script everytime you edit it. A little program build-n-run.cpp presented in this repo solves the problem.

In bash scripts, first line always starts with "shebang" followed by name of a bash interpreter. When you run bash script, effectively bash interpreter is run and this script is passed to it as first argument.

    #!/bin/bash
    echo "Hello world!"

Same approach is used for Python scripts, Scala scripts, etc. So I did the same: example script hello.cpp in this repo is normal C++ program prepended with shebang line:

    #!/usr/local/bin/build-n-run
    #include <stdio.h>
    int main() {
        puts("Hello world!");
    }

build-n-run automatically recompiles script if it is new or edited (i.e. if compiled binary does not exist or if source file's modification time is newer than binary's) and then runs it:

    $ hello.cpp
    Recompiling...    <--- First time you run your script, it's recompiled.
    Hello world!

    $ hello.cpp
    Hello world!      <--- No recompilation on next run if script is unchanged.

Installation and use

1. Download build-n-run.cpp from this repo.

2. (Optional) Check its source code: you might want to update GCC options used to compile your scripts, or remove "Recompiling..." message if it messes with our scripts' output.

3. Compile and install it. I install to /usr/local/bin, so I run this command as root; you can install it anywhere you want, just don't forget to update path in scripts' shebang line. I use gcc 7.3.0, so I explicitly link libstdc++fs.a which implements std::experimental::filesystem.

    # g++ build-n-run.cpp -lstdc++fs -o /usr/local/bin/build-n-run
   

That's all. Now write C++ program with shebang line, chmod it to be executable, and run:

    $ chmod +x hello.cpp
    $ ./hello.cpp
    Recompiling...
    Hello world!

Let's take a look at ~/bin/build-n-run.compiled directory:

    $ ls ~/bin/build-n-run.compiled
    home--me--tmp--hello

I downloaded hello.cpp to /home/me/tmp, and compiled binary's name reflects source's full path, slashes replaced with "--".

Security concerns

Compiled cache is inside user's home, so scripts compiled by one user cannot be run by other users (see issue #1).

Discussions

• linux.org.ru (Russian)

• reddit.com