Executor Plugin for VfxApply
============================

## Scripts

Each script command is named, and will be executed in order of appearance. Errors
will be reported and execution will stop if the exit code is non-zero, using
the names as logical pointers.

    props:
        set:
            <varname>: { value:<expr>, escape:<bool> }
        script:
            <step>:
                info: <string>
                exec: <commmand>
                parse: <parse-expr>


### Command lines

Command line uses placeholders.

        {%input}    The input filename, escaped for the command line
        {%uinput}   Unescaped input filename
        {%output}   The output filename, escaped for command line
        {%uoutput}  Unescaped outptu filename

Any parameters will also be available:

        {%paramname} 

And you can use `set` to assign stuff to variables.


### Setting variables

Setting variables is done using the `set` prop. The core syntax is:

    set:
        myvarname: { value:"MyValue" }

Additionally, `escape` can be used to flag that the value need to be
escaped for the command line.

        myvarname: { value:"SomeValue", escape:true }

Variables set this way can be used for the command line, and the same
expressions can be used to define vars:

    set:
        tempfile: { value:"{%uinput}.tmp", escape:true }
    script:
        first:
            exec "first --temp-file {%tempfile}"


### Parsing output

To parse the output, add a `parse` key to the command block.

        parse:
            regex:    <- expression
            from:     <- stream for comparison (stdout or stderr)
            frame:    <- index of frame number, or leave out
            fps:      <- index of frames per second, or leave out