Command Substitution for the Windows Command Shell

Most Unix-like shells support a technique called command substitution: a way to use the output of one command in the middle of another command. The Windows standard shell (command prompt) lacks this ability, but the csub command provides a simple way to mock this for most situations.

csub [--help|-h|/?] <command> [<strings>] [`<command>`] [<strings>] [`<command>`] …

In most shells, one can accomplish command substitution by quoting a command with backquotes like so:

> echo It's a fine day in `hostname`-land.
It's a fine day in mycomputer03-land.

In other shells, like Bash, you can also accomplish this by enclosing the command in $(…), like this:

> echo It's a fine day in $(hostname)-land.
It's a fine day in mycomputer03-land.

The csub command provides a way to do this in the Windows command shell — anything in the csub arguments between backquotes is executed and replaced with the output, like so:

C:\> csub echo It's a fine day in `hostname`-land.
It's a fine day in mycomputer03-land.

The csub command is executed inside its own context, so commands that would change the environment cannot change the environment of the caller. For example,

C:\qux\baz\frotz> csub cd `echo \qux`

C:\qux\baz\frotz>

In the above example, you'd like the current directory to be C:\qux after running the command. The csub command does change the directory, but only it its own environment; it does not change the environment at the calling level.

This project uses the CMake build tool. CMake is a meta-build system that locates and uses your local development tools to build the project if possible.

To build, first install [CMake][https://cmake.org/]. Then go to the project root directory and run the following command:

cmake -B build

This will locate your installed development tools and configure your project build in the build/ directory. After that, whenever you want a new build, run this command:

cmake --build build

This will build a debug version of the project, located in build/Debug/. To build a release version, run

cmake --build build --config release

You can find the built release executable in build/Release/.

The built executable is csub.exe, and can be copied anywhere to your command path. There is no Windows installation required for this tool.

Steve Hollasch, [email protected]
https://github.com/hollasch/csub