Create Linux Bash and Windows batch scripts simultaneously with Batsh

Arrays

Batsh supports arrays, or variables that store a list of arbitrary data:

a = [1, 2, "hello"];

Batsh numbers the elements in the array consecutively, starting with 0. To access an item in the list, you need to note its index in square brackets. The following line stores 2 from array a in variable b:

b = a[1];

However, Batsh currently does not have any functions that can be used to supplement the array with other elements. The number of elements in an array can only be retrieved using the undocumented len function: length = len(a);. The benefits of arrays are therefore limited.

To Be, or Not To Be

The function exists(), which checks whether a file exists, has proved to be much more useful than readdir() or arrays. In the example shown in Listing 7, exists() first tests whether the file photo1.png is located in the /home/tim/photos/ directory.

Listing 7

Existential Question

 

The value returned by exists() is then checked by the if query: The script follows the instructions between the upper curly brackets if the file exists and the instructions in the curly brackets after else otherwise.

If needed, you can leave out the else. As with while, you can put any logical expression in the parentheses of if (e.g., if (a> b) { ... }.

The problem in Listing 7, however, is that the path specification, /home/tim/photos, is tailored to a Linux system, and the Batsh compiler does not translate it into the appropriate Windows counterpart, as shown in Figure 5.

Figure 5: The Batsh compiler simply uses the path specification /home/tim/photos in the finished batch file.

Batsh cannot even tell your script whether it is running in Bash or Windows, so you have no way to change this behavior. The built-in function bash() can carry out a Bash command assigned to it:

bash("man convert");

The Batsh compiler only translates this function if you can create a Bash script. The selection, man convert, therefore, only appears in the Bash script, not in the Windows batch file. Similarly, the function batch() runs a batch instruction passed in. The Batsh compiler only translates this function if you compile the script for Windows.

To the Source

The Batsh website [3] is not the only place you can compile Batsh programs: The developer has released the compiler source code under an MIT license on GitHub [2].

Batsh was written entirely in the functional programming language OCaml. Therefore, to install the compiler you need a corresponding OCaml environment, which can be found in the repositories of most distributions.

The easiest way to install Batsh is through OCaml's own package manager, OPAM, which you can install on Ubuntu using the opam package:

$ sudo apt-get install opam m4

The m4 package allows you to install some of the additional libraries used by Batsh.

The following command is supposed to load Batsh as soon as these conditions are met:

$ opam install batsh

However, I was unable to resolve the Batsh dependencies automatically on the test machine with Ubuntu 14.10.

An attempt to compile Batsh manually from the source code also failed in the lab for the same reason. To install Batsh, it should be sufficient to set up OCaml using the package manager, then download the current Batsh source code package [3], unzip it, and compile and install it using make and make install. Additional OCaml dependencies are listed on the GitHub site [4].

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