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<h3 class="section">32.2 Reading Passwords</h3>

<p>When reading in a password, it is desirable to avoid displaying it on
the screen, to help keep it secret.  The following function handles this
in a convenient way.

<!-- unistd.h -->
<!-- BSD -->
<div class="defun">
&mdash; Function: char * <b>getpass</b> (<var>const char *prompt</var>)<var><a name="index-getpass-3676"></a></var><br>
<blockquote>
        <p><code>getpass</code> outputs <var>prompt</var>, then reads a string in from the
terminal without echoing it.  It tries to connect to the real terminal,
<samp><span class="file">/dev/tty</span></samp>, if possible, to encourage users not to put plaintext
passwords in files; otherwise, it uses <code>stdin</code> and <code>stderr</code>. 
<code>getpass</code> also disables the INTR, QUIT, and SUSP characters on the
terminal using the <code>ISIG</code> terminal attribute (see <a href="Local-Modes.html#Local-Modes">Local Modes</a>). 
The terminal is flushed before and after <code>getpass</code>, so that
characters of a mistyped password are not accidentally visible.

        <p>In other C libraries, <code>getpass</code> may only return the first
<code>PASS_MAX</code> bytes of a password.  The GNU C library has no limit, so
<code>PASS_MAX</code> is undefined.

        <p>The prototype for this function is in <samp><span class="file">unistd.h</span></samp>.  <code>PASS_MAX</code>
would be defined in <samp><span class="file">limits.h</span></samp>. 
</p></blockquote></div>

   <p>This precise set of operations may not suit all possible situations.  In
this case, it is recommended that users write their own <code>getpass</code>
substitute.  For instance, a very simple substitute is as follows:

<pre class="smallexample">     #include &lt;termios.h&gt;
     #include &lt;stdio.h&gt;
     
     ssize_t
     my_getpass (char **lineptr, size_t *n, FILE *stream)
     {
       struct termios old, new;
       int nread;
     
       /* <span class="roman">Turn echoing off and fail if we can't.</span> */
       if (tcgetattr (fileno (stream), &amp;old) != 0)
         return -1;
       new = old;
       new.c_lflag &amp;= ~ECHO;
       if (tcsetattr (fileno (stream), TCSAFLUSH, &amp;new) != 0)
         return -1;
     
       /* <span class="roman">Read the password.</span> */
       nread = getline (lineptr, n, stream);
     
       /* <span class="roman">Restore terminal.</span> */
       (void) tcsetattr (fileno (stream), TCSAFLUSH, &amp;old);
     
       return nread;
     }
</pre>
   <p>The substitute takes the same parameters as <code>getline</code>
(see <a href="Line-Input.html#Line-Input">Line Input</a>); the user must print any prompt desired.

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