|
|
# Scripts
|
|
|
|
|
|
Racket files can be turned into executable scripts on Unix and Mac OS.
|
|
|
On Windows, a compatibility layer like Cygwin support the same kind of
|
|
|
scripts, or scripts can be implemented as batch files.
|
|
|
|
|
|
## 1. Unix Scripts
|
|
|
|
|
|
In a Unix environment \(including Linux and Mac OS\), a Racket file can
|
|
|
be turned into an executable script using the shell’s `#!` convention.
|
|
|
The first two characters of the file must be `#!`; the next character
|
|
|
must be either a space or `/`, and the remainder of the first line must
|
|
|
be a command to execute the script. For some platforms, the total length
|
|
|
of the first line is restricted to 32 characters, and sometimes the
|
|
|
space is required.
|
|
|
|
|
|
> Use `#lang` `racket/base` instead of `#lang` `racket` to produce scripts
|
|
|
> with a faster startup time.
|
|
|
|
|
|
The simplest script format uses an absolute path to a `racket`
|
|
|
executable followed by a module declaration. For example, if `racket` is
|
|
|
installed in `"/usr/local/bin"`, then a file containing the following
|
|
|
text acts as a “hello world” script:
|
|
|
|
|
|
`#! /usr/local/bin/racket`
|
|
|
`#lang racket/base`
|
|
|
`"Hello, world!"`
|
|
|
|
|
|
In particular, if the above is put into a file `"hello"` and the file is
|
|
|
made executable \(e.g., with `chmod a+x hello`\), then typing `./hello`
|
|
|
at the shell prompt produces the output `"Hello, world!"`.
|
|
|
|
|
|
The above script works because the operating system automatically puts
|
|
|
the path to the script as the argument to the program started by the
|
|
|
`#!` line, and because `racket` treats a single non-flag argument as a
|
|
|
file containing a module to run.
|
|
|
|
|
|
Instead of specifying a complete path to the `racket` executable, a
|
|
|
popular alternative is to require that `racket` is in the user’s command
|
|
|
path, and then “trampoline” using `/usr/bin/env`:
|
|
|
|
|
|
`#! /usr/bin/env racket`
|
|
|
`#lang racket/base`
|
|
|
`"Hello, world!"`
|
|
|
|
|
|
In either case, command-line arguments to a script are available via
|
|
|
`current-command-line-arguments`:
|
|
|
|
|
|
`#! /usr/bin/env racket`
|
|
|
`#lang racket/base`
|
|
|
`(printf "Given arguments: ~s\n"`
|
|
|
`(current-command-line-arguments))`
|
|
|
|
|
|
If the name of the script is needed, it is available via
|
|
|
`(find-system-path 'run-file)`, instead of via
|
|
|
`(current-command-line-arguments)`.
|
|
|
|
|
|
Usually, the best way to handle command-line arguments is to parse them
|
|
|
using the `command-line` form provided by `racket`. The `command-line`
|
|
|
form extracts command-line arguments from
|
|
|
`(current-command-line-arguments)` by default:
|
|
|
|
|
|
`#! /usr/bin/env racket`
|
|
|
`#lang racket`
|
|
|
|
|
|
`(define verbose? (make-parameter #f))`
|
|
|
|
|
|
`(define greeting`
|
|
|
`(command-line`
|
|
|
`#:once-each`
|
|
|
`[("-v") "Verbose mode" (verbose? #t)]`
|
|
|
`#:args`
|
|
|
`(str) str))`
|
|
|
|
|
|
`(printf "~a~a\n"`
|
|
|
`greeting`
|
|
|
`(if (verbose?) " to you, too!" ""))`
|
|
|
|
|
|
Try running the above script with the `--help` flag to see what
|
|
|
command-line arguments are allowed by the script.
|
|
|
|
|
|
An even more general trampoline uses `/bin/sh` plus some lines that are
|
|
|
comments in one language and expressions in the other. This trampoline
|
|
|
is more complicated, but it provides more control over command-line
|
|
|
arguments to `racket`:
|
|
|
|
|
|
`#! /bin/sh`
|
|
|
`#|`
|
|
|
`exec racket -e '(printf "Running...\n")' -u "$0" ${1+"$@"}`
|
|
|
`|#`
|
|
|
`#lang racket/base`
|
|
|
`(printf "The above line of output had been produced via\n")`
|
|
|
`(printf "a use of the `-e' flag.\n")`
|
|
|
`(printf "Given arguments: ~s\n"`
|
|
|
`(current-command-line-arguments))`
|
|
|
|
|
|
Note that `#!` starts a line comment in Racket, and `#|`...`|#` forms a
|
|
|
block comment. Meanwhile, `#` also starts a shell-script comment, while
|
|
|
`exec racket` aborts the shell script to start `racket`. That way, the
|
|
|
script file turns out to be valid input to both `/bin/sh` and `racket`.
|
|
|
|
|
|
## 2. Windows Batch Files
|
|
|
|
|
|
A similar trick can be used to write Racket code in Windows `.bat` batch
|
|
|
files:
|
|
|
|
|
|
`; @echo off`
|
|
|
`; Racket.exe "%~f0" %*`
|
|
|
`; exit /b`
|
|
|
`#lang racket/base`
|
|
|
`"Hello, world!"`
|