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