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# Chapter 14 The OSH shell

- Startup
- Aliases
- Interactive syntax

OMake also includes a standalone command-line interpreter `osh` that can be used as an interactive shell. The shell uses the same syntax, and provides the same features on all platforms `omake` supports, including Win32.

## 14.1 Startup

On startup, `osh` reads the file `~/.oshrc` if it exists. The syntax of this file is the same as an `OMakefile`. The following additional variables are significant.

##### prompt

The `prompt` variable specifies the command-line prompt. It can be a simple string.

        prompt = osh>

Or you may choose to define it as a function of no arguments.

        prompt() =
            return $"<$(USER):$(HOST) $(homename $(CWD))>"

An example of the latter prompt is as follows.

        <jyh:kenai.yapper.org ~>cd links/omake
        <jyh:kenai.yapper.org ~/links/omake>

If you include any "invisible" text in the prompt (such as various terminal escape sequences), they must be wrapped using the `prompt-invisible` function. For example, to create a bold prompt on terminals that support it, you can use the following.

        prompt =
           bold-begin = $(prompt-invisible $(tgetstr bold))
           bold-end = $(prompt-invisible $(tgetstr sgr0))
           value $(bold-begin)$"osh>"$(bold-end)

##### ignoreeof

If the `ignoreeof` is `true`, then `osh` will not exit on a terminal end-of-file (usually `^D` on Unix systems).

## 14.2 Aliases

Command aliases are defined by adding functions to the `Shell.` object. The following alias adds the `-AF` option to the `ls` command.

        Shell. +=
           ls(argv) =
              "ls" -AF $(argv)

Quoted commands do not undergo alias expansion. The quotation `"ls"` prevents the alias from being recursive.

## 14.3 Interactive syntax

The interactive syntax in `osh` is the same as the syntax of an `OMakefile`, with one exception in regard to indentation. The line before an indented block must have a colon at the end of the line. A block is terminated with a `.` on a line by itself, or `^D`. In the following example, the first line `if true` has no body, because there is no colon.

       # The following if has no body
       osh>if true
       # The following if has a body
       osh>if true:
       if>       if true:
       if>          println(Hello world)
       if>          .
       Hello world

Note that `osh` makes some effort to modify the prompt while in an indented body, and it auto-indents the text.

The colon signifier is also allowed in files, although it is not required.

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