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<concept xml:lang="en" id="GUID-00FFF2B3-F8E4-5CBF-B031-240D98BB2111"><title>External Programs</title><prolog><metadata><keywords/></metadata></prolog><conbody><p>External programs are executables built outside but which can be launched from the Zsh command prompt. </p> <p>If the command is neither built-in, nor specified with an absolute pathname, the shell will look in the <filepath>\sys\bin</filepath> on each drive in reverse alphabetical order (<filepath>y:</filepath>, <filepath>x:</filepath>,... to <filepath>b:</filepath>, <filepath>a:</filepath> and later <filepath>z:</filepath>) and execute the first external program found. </p> <p>To execute the external program directly give the following command at the command-prompt: </p> <p><userinput>command &lt;ext_pgm&gt;</userinput> </p> <p>where <codeph>ext_pgm</codeph> is the name of the external program. </p> <p>For example: </p> <p>The program below reads input from Zsh and writes data to Zsh which can then be redirected back to the Telnet client. </p> <codeblock id="GUID-2A92BFF9-D69D-5C18-B657-9D7D5738EA22" xml:space="preserve">#include &lt;stdio.h&gt;

#include <string.h>

#include <unistd.h>

int  main()

    {

    char userData[20]; char ch; int x=0;

    memset(userData,0,20);

    x=read(0,userData, 20);    

    while(strcmp(userData, "quit"))

        {

        write(1, userData, x);

        memset(userData,0,20);

        x=read(0,userData, 20);        

        }        

    return 0;                 

    }