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>Chapter 4. Other ways of running Hugs</H1
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="RUNHUGS"
>4.1. Running standalone Haskell programs</A
></H1
><P
><B
CLASS="COMMAND"
>runhugs</B
> [<TT
CLASS="REPLACEABLE"
><I
>option</I
></TT
>...] <TT
CLASS="REPLACEABLE"
><I
>file</I
></TT
> [<TT
CLASS="REPLACEABLE"
><I
>argument</I
></TT
>...]</P
><P
>The <B
CLASS="COMMAND"
>runhugs</B
> command is an interpreter for an executable Hugs
script.
The first non-option should be the name of a file containing a Haskell
<TT
CLASS="LITERAL"
>Main</TT
> module.
The <B
CLASS="COMMAND"
>runhugs</B
> command will invoke the
the <CODE
CLASS="FUNCTION"
>main</CODE
> function in this module, with any subsequent
arguments available through the <CODE
CLASS="FUNCTION"
>getArgs</CODE
> action.</P
><P
>For example, suppose we have a file <TT
CLASS="FILENAME"
>echo.hs</TT
> containing
<PRE
CLASS="PROGRAMLISTING"
>module Main where
import System.Environment
main = do
args <- getArgs
putStrLn (unwords args)</PRE
>
Then we can run this program with the command
<PRE
CLASS="SCREEN"
>runhugs echo.hs a b c</PRE
>
We can also test the program from within the interpreter
using the <CODE
CLASS="FUNCTION"
>withArgs</CODE
> function from the
<TT
CLASS="LITERAL"
>System.Environment</TT
> module:
<PRE
CLASS="SCREEN"
>Main> withArgs ["a", "b", "c"] main
a b c</PRE
></P
><P
>On Unix systems, it is possible for an executable file to specify which
program is used to run it.
To do this we need to make the module a literate script, like the following:
<PRE
CLASS="PROGRAMLISTING"
>#! /usr/local/bin/runhugs +l
> module Main where
> import System.Environment
> main = do
> args <- getArgs
> putStrLn (unwords args)</PRE
>
If this file is called <TT
CLASS="FILENAME"
>myecho</TT
>, and is executable,
we can say
<PRE
CLASS="SCREEN"
>myecho a b c</PRE
>
This invokes the command
<PRE
CLASS="SCREEN"
>/usr/local/bin/runhugs +l myecho a b c</PRE
>
The <A
HREF="options.html#OPTION-LITERATE"
><CODE
CLASS="OPTION"
>+l</CODE
></A
> option tells
<B
CLASS="COMMAND"
>runhugs</B
> that <TT
CLASS="FILENAME"
>myecho</TT
> contains a
literate script,
even though its name does not end in <SPAN
CLASS="QUOTE"
>"<TT
CLASS="LITERAL"
>.lhs</TT
>"</SPAN
>.</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>Unfortunately, the <TT
CLASS="LITERAL"
>#!</TT
> feature passes additional arguments
(if any) to the program as a single argument: if the first line were
<PRE
CLASS="PROGRAMLISTING"
>#! /usr/local/bin/runhugs +l -98</PRE
>
then the first argument to <B
CLASS="COMMAND"
>runhugs</B
> would be
<SPAN
CLASS="QUOTE"
>"<TT
CLASS="LITERAL"
>+l -98</TT
>"</SPAN
>.
You can get around this using the
<A
HREF="options.html#OPTION-SPLIT-OPTIONS"
><CODE
CLASS="OPTION"
>-X</CODE
></A
> option,
which asks for the string to be split into options:
<PRE
CLASS="PROGRAMLISTING"
>#! /usr/local/bin/runhugs -X +l -98</PRE
>
Then the program will read and act on both the <CODE
CLASS="OPTION"
>+l</CODE
> and
<CODE
CLASS="OPTION"
>-98</CODE
> options.</P
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