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发信人: georgehill (人生不定式), 信区: Linux
标 题: Unix Programming FAQ (v1.37)-Miscellan(转寄)
发信站: BBS 荔园晨风站 (Thu Sep 14 13:02:33 2000), 站内信件
【 以下文字转载自 georgehill 的信箱 】
【 原文由 georgehill.bbs@smth.org 所发表 】
发信人: hhuu (什么是水，就是water啊), 信区: FreeBSD
标 题: Unix Programming FAQ (v1.37)-Miscellan(转寄)
发信站: BBS 水木清华站 (Wed Sep 13 20:52:36 2000)
发信人: Luther (天語『至菜※努力』), 信区: Security
标 题: Unix Programming FAQ (v1.37)-Miscellan(转寄)
发信站: 武汉白云黄鹤站 (Wed Sep 13 15:47:24 2000), 站内信件
5. Miscellaneous programming
****************************
5.1 How do I compare strings using wildcards?
=============================================
The answer to *that* depends on what exactly you mean by `wildcards'.
There are two quite different concepts that qualify as `wildcards'. They
are:
*Filename patterns*
These are what the shell uses for filename expansion (`globbing').
*Regular Expressions*
These are used by editors, `grep', etc. for matching text, but they
normally *aren't* applied to filenames.
5.1.1 How do I compare strings using filename patterns?
-------------------------------------------------------
Unless you are unlucky, your system should have a function `fnmatch()' to
do filename matching. This generally allows only the Bourne shell style of
pattern; i.e. it recognises `*', `[...]' and `?', but probably won't
pattern; i.e. it recognises `*', `[...]' and `?', but probably won't
support the more arcane patterns available in the Korn and Bourne-Again
shells.
If you don't have this function, then rather than reinvent the wheel, you
are probably better off snarfing a copy from the BSD or GNU sources.
Also, for the common cases of matching actual filenames, look for `glob()',
which will find all existing files matching a pattern.
5.1.2 How do I compare strings using regular expressions?
---------------------------------------------------------
There are a number of slightly different syntaxes for regular expressions;
most systems use at least two: the one recognised by `ed', sometimes known
as `Basic Regular Expressions', and the one recognised by `egrep',
`Extended Regular Expressions'. Perl has it's own slightly different
flavour, as does Emacs.
To support this multitude of formats, there is a corresponding multitude of
implementations. Systems will generally have regexp-matching functions
(usually `regcomp()' and `regexec()') supplied, but be wary; some systems
have more than one implementation of these functions available, with
different interfaces. In addition, there are many library implementations
available. (It's common, BTW, for regexps to be compiled to an internal
form before use, on the assumption that you may compare several separate
strings against the same regexp.)
One library available for this is the `rx' library, available from the GNU
One library available for this is the `rx' library, available from the GNU
mirrors. This seems to be under active development, which may be a good or
a bad thing depending on your point of view :-)
5.2 What's the best way to send mail from a program?
====================================================
There are several ways to send email from a Unix program. Which is the best
method to use in a given situation varies, so I'll present two of them. A
third possibility, not covered here, is to connect to a local SMTP port (or
a smarthost) and use SMTP directly; see RFC 821.
5.2.1 The simple method: /bin/mail
----------------------------------
For simple applications, it may be sufficient to invoke `mail' (usually
`/bin/mail', but could be `/usr/bin/mail' on some systems).
*WARNING:* Some versions of UCB Mail may execute commands prefixed by `~!'
or `~|' given in the message body even in non-interactive mode. This can be
a security risk.
Invoked as `mail -s 'subject' recipients...' it will take a message body on
standard input, and supply a default header (including the specified
subject), and pass the message to `sendmail' for delivery.
This example mails a test message to `root' on the local system:
#include <stdio.h>
#define MAILPROG "/bin/mail"
#define MAILPROG "/bin/mail"
int main()
{
FILE *mail = popen(MAILPROG " -s 'Test Message' root", "w");
if (!mail)
{
perror("popen");
exit(1);
}
fprintf(mail, "This is a test.\n");
if (pclose(mail))
{
fprintf(stderr, "mail failed!\n");
exit(1);
}
}
If the text to be sent is already in a file, then one can do:
system(MAILPROG " -s 'file contents' root </tmp/filename");
These methods can be extended to more complex cases, but there are many
pitfalls to watch out for:
pitfalls to watch out for:
* If using system() or popen(), you must be very careful about quoting
arguments to protect them from filename expansion or word splitting
* Constructing command lines from user-specified data is a common source
of buffer-overrun errors and other security holes
* This method does not allow for CC: or BCC: recipients to be specified
(some versions of /bin/mail may allow this, some do not)
5.2.2 Invoking the MTA directly: /usr/lib/sendmail
--------------------------------------------------
The `mail' program is an example of a "Mail User Agent", a program intended
to be invoked by the user to send and receive mail, but which does not
handle the actual transport. A program for transporting mail is called an
"MTA", and the most commonly found MTA on Unix systems is called
`sendmail'. There are other MTAs in use, such as `MMDF', but these
generally include a program that emulates the usual behaviour of `sendmail'.
Historically, `sendmail' has usually been found in `/usr/lib', but the
current trend is to move library programs out of `/usr/lib' into
directories such as `/usr/sbin' or `/usr/libexec'. As a result, one
normally invokes `sendmail' by its full path, which is system-dependent.
To understand how `sendmail' behaves, it's useful to understand the concept
of an "envelope". This is very much like paper mail; the envelope defines
who the message is to be delivered to, and who it is from (for the purpose
of reporting errors). Contained in the envelope are the "headers", and the
of reporting errors). Contained in the envelope are the "headers", and the
"body", separated by a blank line. The format of the headers is specified
primarily by RFC 822; see also the MIME RFCs.
There are two main ways to use `sendmail' to originate a message: either
the envelope recipients can be explicitly supplied, or `sendmail' can be
instructed to deduce them from the message headers. Both methods have
advantages and disadvantages.
5.2.2.1 Supplying the envelope explicitly
.........................................
The recipients of a message can simply be specified on the command line.
This has the drawback that mail addresses can contain characters that give
`system()' and `popen()' considerable grief, such as single quotes, quoted
strings etc. Passing these constructs successfully through shell
interpretation presents pitfalls. (One can do it by replacing any single
quotes by the sequence single-quote backslash single-quote single-quote,
then surrounding the entire address with single quotes. Ugly, huh?)
Some of this unpleasantness can be avoided by eschewing the use of
`system()' or `popen()', and resorting to `fork()' and `exec()' directly.
This is sometimes necessary in any event; for example, user-installed
handlers for SIGCHLD will usually break `pclose()' to a greater or lesser
extent.
Here's an example:
#include <sys/types.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sysexits.h>
/* #include <paths.h> if you have it */
#ifndef _PATH_SENDMAIL
#define _PATH_SENDMAIL "/usr/lib/sendmail"
#endif
/* -oi means "dont treat . as a message terminator"
* remove ,"--" if using a pre-V8 sendmail (and hope that no-one
* ever uses a recipient address starting with a hyphen)
* you might wish to add -oem (report errors by mail)
*/
#define SENDMAIL_OPTS "-oi","--"
/* this is a macro for returning the number of elements in array */
#define countof(a) ((sizeof(a))/sizeof((a)[0]))
#define countof(a) ((sizeof(a))/sizeof((a)[0]))
/* send the contents of the file open for reading on FD to the
* specified recipients; the file is assumed to contain RFC822 headers
* & body, the recipient list is terminated by a NULL pointer; returns
* -1 if error detected, otherwise the return value from sendmail
* (which uses <sysexits.h> to provide meaningful exit codes)
*/
int send_message(int fd, const char **recipients)
{
static const char *argv_init[] = { _PATH_SENDMAIL, SENDMAIL_OPTS };
const char **argvec = NULL;
int num_recip = 0;
pid_t pid;
int rc;
int status;
/* count number of recipients */
while (recipients[num_recip])
++num_recip;
if (!num_recip)
return 0; /* sending to no recipients is successful */
/* alloc space for argument vector */
argvec = malloc((sizeof char*) * (num_recip+countof(argv_init)+1));
if (!argvec)
return -1;
/* initialise argument vector */
memcpy(argvec, argv_init, sizeof(argv_init));
memcpy(argvec+countof(argv_init),
recipients, num_recip*sizeof(char*));
argvec[num_recip + countof(argv_init)] = NULL;
/* may need to add some signal blocking here. */
/* fork */
switch (pid = fork())
{
{
case 0: /* child */
/* Plumbing */
if (fd != STDIN_FILENO)
dup2(fd, STDIN_FILENO);
/* defined elsewhere -- closes all FDs >= argument */
closeall(3);
/* go for it: */
execv(_PATH_SENDMAIL, argvec);
_exit(EX_OSFILE);
default: /* parent */
free(argvec);
rc = waitpid(pid, &status, 0);
if (rc < 0)
return -1;
if (WIFEXITED(status))
return WEXITSTATUS(status);
return -1;
return -1;
case -1: /* error */
free(argvec);
return -1;
}
}
5.2.2.2 Allowing sendmail to deduce the recipients
..................................................
The `-t' option to `sendmail' instructs `sendmail' to parse the headers of
the message, and use all the recipient-type headers (i.e. `To:', `Cc:' and
`Bcc:') to construct the list of envelope recipients. This has the
advantage of simplifying the `sendmail' command line, but makes it
impossible to specify recipients other than those listed in the headers.
(This is not usually a problem.)
As an example, here's a program to mail a file on standard input to
specified recipients as a MIME attachment. Some error checks have been
omitted for brevity. This requires the `mimencode' program from the
`metamail' distribution.
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
/* #include <paths.h> if you have it */
/* #include <paths.h> if you have it */
#ifndef _PATH_SENDMAIL
#define _PATH_SENDMAIL "/usr/lib/sendmail"
#endif
#define SENDMAIL_OPTS "-oi"
#define countof(a) ((sizeof(a))/sizeof((a)[0]))
char tfilename[L_tmpnam];
char command[128+L_tmpnam];
void cleanup(void)
{
unlink(tfilename);
}
int main(int argc, char **argv)
{
FILE *msg;
int i;
if (argc < 2)
if (argc < 2)
{
fprintf(stderr, "usage: %s recipients...\n", argv[0]);
exit(2);
}
if (tmpnam(tfilename) == NULL
|| (msg = fopen(tfilename,"w")) == NULL)
exit(2);
atexit(cleanup);
fclose(msg);
msg = fopen(tfilename,"a");
if (!msg)
exit(2);
/* construct recipient list */
fprintf(msg, "To: %s", argv[1]);
for (i = 2; i < argc; i++)
fprintf(msg, ",\n\t%s", argv[i]);
fputc('\n',msg);
fputc('\n',msg);
/* Subject */
fprintf(msg, "Subject: file sent by mail\n");
/* sendmail can add it's own From:, Date:, Message-ID: etc. */
/* MIME stuff */
fprintf(msg, "MIME-Version: 1.0\n");
fprintf(msg, "Content-Type: application/octet-stream\n");
fprintf(msg, "Content-Transfer-Encoding: base64\n");
/* end of headers -- insert a blank line */
fputc('\n',msg);
fclose(msg);
/* invoke encoding program */
sprintf(command, "mimencode -b >>%s", tfilename);
if (system(command))
exit(1);
/* invoke mailer */
sprintf(command, "%s %s -t <%s",
_PATH_SENDMAIL, SENDMAIL_OPTS, tfilename);
if (system(command))
exit(1);
return 0;
}
--
║ ◇ 系統 ◇ ║ ¤ FreeBSD ¤ ║ --=【紅色小魔鬼】=-- ║ Ｗｅｌｃｏｍｅ ║
※ 来源:．武汉白云黄鹤站 bbs.whnet.edu.cn．[FROM: 202.112.20.201]
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※ 转载:．武汉白云黄鹤站 bbs.whnet.edu.cn．[FROM: 202.112.20.201]
--
行列中 作不朽文章
谈笑间 论古今英雄
痴狂里 诉红尘情爱
来去时 不枉一生风流
--------- bbs.ntu.edu.tw
※ 修改:·hhuu 於 Sep 13 20:53:16 修改本文·[FROM: 166.111.160.6]
※ 来源:·BBS 水木清华站 smth.org·[FROM: 166.111.160.6]
--
※ 转载:·BBS 荔园晨风站 bbs.szu.edu.cn·[FROM: 192.168.1.115]
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