1ReadPassword(3) User Contributed Perl Documentation ReadPassword(3)
2
6 Term::ReadPassword - Asking the user for a password
7
9 use Term::ReadPassword;
10 while (1) {
11 my $password = read_password('password: ');
12 redo unless defined $password;
13 if ($password eq 'flubber') {
14 print "Access granted.\n";
15 last;
16 } else {
17 print "Access denied.\n";
18 redo;
19 }
20 }
21
23 This module lets you ask the user for a password in the traditional
24 way, from the keyboard, without echoing.
25 This is not intended for use over the web; user authentication over the
27 web is another matter entirely. Also, this module should generally be
28 used in conjunction with Perl's crypt() function, sold separately.
29 The read_password function prompts for input, reads a line of text from
31 the keyboard, then returns that line to the caller. The line of text
32 doesn't include the newline character, so there's no need to use chomp.
33 While the user is entering the text, a few special characters are
35 processed. The character delete (or the character backspace) will back
36 up one character, removing the last character in the input buffer (if
37 any). The character CR (or the character LF) will signal the end of
38 input, causing the accumulated input buffer to be returned. Control-U
39 will empty the input buffer. And, optionally, the character Control-C
40 may be used to terminate the input operation. (See details below.) All
41 other characters, even ones which would normally have special purposes,
42 will be added to the input buffer.
43 It is not recommended, though, that you use the as-yet-unspecified
45 control characters in your passwords, as those characters may become
46 meaningful in a future version of this module. Applications which allow
47 the user to set their own passwords may wish to enforce this rule,
48 perhaps with code something like this:
49 {
51 # Naked block for scoping and redo
52 my $new_pw = read_password("Enter your new password: ");
53 if ($new_pw =~ /([^\x20-\x7E])/) {
54 my $bad = unpack "H*", $1;
55 print "Your password may not contain the ";
56 print "character with hex code $bad.\n";
57 redo;
58 } elsif (length($new_pw) < 5) {
59 print "Your password must be longer than that!\n";
60 redo;
61 } elsif ($new_pw ne read_password("Enter it again: ")) {
62 print "Passwords don't match.\n";
63 redo;
64 } else {
65 &change_password($new_pw);
66 print "Your password is now changed.\n";
67 }
68 }
69 The second parameter to read_password is the optional "idle_timeout"
71 value. If it is a non-zero number and there is no keyboard input for
72 that many seconds, the input operation will terminate. Notice that this
73 is not an overall time limit, as the timer is restarted with each new
74 character.
75 The third parameter will optionally allow the input operation to be
77 terminated by the user with Control-C. If this is not supplied, or is
78 false, a typed Control-C will be entered into the input buffer just as
79 any other character. In that case, there is no way from the keyboard to
80 terminate the program while it is waiting for input. (That is to say,
81 the normal ability to generate signals from the keyboard is suspended
82 during the call to read_password.)
83 If the input operation terminates early (either because the
85 idle_timeout was exceeded, or because a Control-C was enabled and
86 typed), the return value will be "undef". In either case, there is no
87 way provided to discover what (if anything) was typed before the early
88 termination, or why the input operation was terminated.
89 So as to discourage users from typing their passwords anywhere except
91 at the prompt, any input which has been "typed ahead" before the prompt
92 appears will be discarded. And whether the input operation terminates
93 normally or not, a newline character will be printed, so that the
94 cursor will not remain on the line after the prompt.
95
97 Windows users will want Term::ReadPassword::Win32.
98 This module has a poorly-designed interface, and should be thoroughly
100 rethought and probably re-united with the Windows version.
101 Users who wish to see password characters echoed as stars may set
103 $Term::ReadPassword::USE_STARS to a true value. The bugs are that some
104 terminals may not erase stars when the user corrects an error, and that
105 using stars leaks information to shoulder-surfers.
106
108 You would think that a module dealing with passwords would be full of
109 security features. You'd think that, but you'd be wrong. For example,
110 perl provides no way to erase a piece of data from memory. (It's easy
111 to erase it so that it can't be accessed from perl, but that's not the
112 same thing as expunging it from the actual memory.) If you've entered a
113 password, even if the variable that contained that password has been
114 erased, it may be possible for someone to find that password, in
115 plaintext, in a core dump. And that's just one potential security hole.
116 In short, if serious security is an issue, don't use this module.
118
120 This program is free software; you may redistribute it, modify it, or
121 both, under the same terms as Perl itself.
122
124 Tom Phoenix <rootbeer@redcat.com>. Copyright (C) 2007 Tom Phoenix.
125
127 Term::ReadLine, "crypt" in perlfunc, and your system's manpages for the
128 low-level I/O operations used here.
129perl v5.12.0 2007-12-14 ReadPassword(3)