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pipe

convert XML file to a format easier to parse with Perl or AWK


  1. pipe.1.man
  2. pipe.2.man
  3. pipe.7.man
  4. pipe.8.man


1. pipe.1.man

Manpage of man

man

Section: User Commands (1)
Updated: 31 Mar 2000
Index Return to Main Contents
 

NAME

pipe - convert XML file to a format easier to parse with Perl or AWK  

SYNOPSIS

pipe [ -l ] [ -- ] [ file ]  

DESCRIPTION

[ToDo]


 

Index

NAME
SYNOPSIS
DESCRIPTION

This document was created by man2html using the manual pages.
Time: 17:32:02 GMT, October 23, 2013

2. pipe.2.man

Manpage of PIPE

PIPE

Section: Linux Programmer's Manual (2)
Updated: 2010-09-10
Index Return to Main Contents
 

NAME

pipe, pipe2 - create pipe  

SYNOPSIS

#include <unistd.h>

int pipe(int pipefd[2]);

#define _GNU_SOURCE             /* See feature_test_macros(7) */
#include <unistd.h>

int pipe2(int pipefd[2], int flags);
 

DESCRIPTION

pipe() creates a pipe, a unidirectional data channel that can be used for interprocess communication. The array pipefd is used to return two file descriptors referring to the ends of the pipe. pipefd[0] refers to the read end of the pipe. pipefd[1] refers to the write end of the pipe. Data written to the write end of the pipe is buffered by the kernel until it is read from the read end of the pipe. For further details, see pipe(7).

If flags is 0, then pipe2() is the same as pipe(). The following values can be bitwise ORed in flags to obtain different behavior:

O_NONBLOCK
Set the O_NONBLOCK file status flag on the two new open file descriptions. Using this flag saves extra calls to fcntl(2) to achieve the same result.
O_CLOEXEC
Set the close-on-exec (FD_CLOEXEC) flag on the two new file descriptors. See the description of the same flag in open(2) for reasons why this may be useful.
 

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.  

ERRORS

EFAULT
pipefd is not valid.
EINVAL
(pipe2()) Invalid value in flags.
EMFILE
Too many file descriptors are in use by the process.
ENFILE
The system limit on the total number of open files has been reached.
 

VERSIONS

pipe2() was added to Linux in version 2.6.27; glibc support is available starting with version 2.9.  

CONFORMING TO

pipe(): POSIX.1-2001.

pipe2() is Linux-specific.  

EXAMPLE

The following program creates a pipe, and then fork(2)s to create a child process; the child inherits a duplicate set of file descriptors that refer to the same pipe. After the fork(2), each process closes the descriptors that it doesn't need for the pipe (see pipe(7)). The parent then writes the string contained in the program's command-line argument to the pipe, and the child reads this string a byte at a time from the pipe and echoes it on standard output.

#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

int
main(int argc, char *argv[])
{
    int pipefd[2];
    pid_t cpid;
    char buf;

    if (argc != 2) {
        fprintf(stderr, "Usage: %s <string>
", argv[0]); exit(EXIT_FAILURE); } if (pipe(pipefd) == -1) { perror("pipe"); exit(EXIT_FAILURE); } cpid = fork(); if (cpid == -1) { perror("fork"); exit(EXIT_FAILURE); } if (cpid == 0) { /* Child reads from pipe */ close(pipefd[1]); /* Close unused write end */ while (read(pipefd[0], &buf, 1) > 0) write(STDOUT_FILENO, &buf, 1); write(STDOUT_FILENO, "
", 1); close(pipefd[0]); _exit(EXIT_SUCCESS); } else { /* Parent writes argv[1] to pipe */ close(pipefd[0]); /* Close unused read end */ write(pipefd[1], argv[1], strlen(argv[1])); close(pipefd[1]); /* Reader will see EOF */ wait(NULL); /* Wait for child */ exit(EXIT_SUCCESS); } }
 

SEE ALSO

fork(2), read(2), socketpair(2), write(2), popen(3), pipe(7)  

COLOPHON

This page is part of release 3.32 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
VERSIONS
CONFORMING TO
EXAMPLE
SEE ALSO
COLOPHON

This document was created by man2html using the manual pages.
Time: 17:32:02 GMT, October 23, 2013

3. pipe.7.man

Manpage of PIPE

PIPE

Section: Linux Programmer's Manual (7)
Updated: 2005-12-08
Index Return to Main Contents
 

NAME

pipe - overview of pipes and FIFOs  

DESCRIPTION

Pipes and FIFOs (also known as named pipes) provide a unidirectional interprocess communication channel. A pipe has a read end and a write end. Data written to the write end of a pipe can be read from the read end of the pipe.

A pipe is created using pipe(2), which creates a new pipe and returns two file descriptors, one referring to the read end of the pipe, the other referring to the write end. Pipes can be used to create a communication channel between related processes; see pipe(2) for an example.

A FIFO (short for First In First Out) has a name within the file system (created using mkfifo(3)), and is opened using open(2). Any process may open a FIFO, assuming the file permissions allow it. The read end is opened using the O_RDONLY flag; the write end is opened using the O_WRONLY flag. See fifo(7) for further details. Note: although FIFOs have a pathname in the file system, I/O on FIFOs does not involve operations on the underlying device (if there is one).  

I/O on Pipes and FIFOs

The only difference between pipes and FIFOs is the manner in which they are created and opened. Once these tasks have been accomplished, I/O on pipes and FIFOs has exactly the same semantics.

If a process attempts to read from an empty pipe, then read(2) will block until data is available. If a process attempts to write to a full pipe (see below), then write(2) blocks until sufficient data has been read from the pipe to allow the write to complete. Nonblocking I/O is possible by using the fcntl(2) F_SETFL operation to enable the O_NONBLOCK open file status flag.

The communication channel provided by a pipe is a byte stream: there is no concept of message boundaries.

If all file descriptors referring to the write end of a pipe have been closed, then an attempt to read(2) from the pipe will see end-of-file (read(2) will return 0). If all file descriptors referring to the read end of a pipe have been closed, then a write(2) will cause a SIGPIPE signal to be generated for the calling process. If the calling process is ignoring this signal, then write(2) fails with the error EPIPE. An application that uses pipe(2) and fork(2) should use suitable close(2) calls to close unnecessary duplicate file descriptors; this ensures that end-of-file and SIGPIPE/EPIPE are delivered when appropriate.

It is not possible to apply lseek(2) to a pipe.  

Pipe Capacity

A pipe has a limited capacity. If the pipe is full, then a write(2) will block or fail, depending on whether the O_NONBLOCK flag is set (see below). Different implementations have different limits for the pipe capacity. Applications should not rely on a particular capacity: an application should be designed so that a reading process consumes data as soon as it is available, so that a writing process does not remain blocked.

In Linux versions before 2.6.11, the capacity of a pipe was the same as the system page size (e.g., 4096 bytes on i386). Since Linux 2.6.11, the pipe capacity is 65536 bytes.  

PIPE_BUF

POSIX.1-2001 says that write(2)s of less than PIPE_BUF bytes must be atomic: the output data is written to the pipe as a contiguous sequence. Writes of more than PIPE_BUF bytes may be nonatomic: the kernel may interleave the data with data written by other processes. POSIX.1-2001 requires PIPE_BUF to be at least 512 bytes. (On Linux, PIPE_BUF is 4096 bytes.) The precise semantics depend on whether the file descriptor is nonblocking (O_NONBLOCK), whether there are multiple writers to the pipe, and on n, the number of bytes to be written:
O_NONBLOCK disabled, n <= PIPE_BUF
All n bytes are written atomically; write(2) may block if there is not room for n bytes to be written immediately
O_NONBLOCK enabled, n <= PIPE_BUF
If there is room to write n bytes to the pipe, then write(2) succeeds immediately, writing all n bytes; otherwise write(2) fails, with errno set to EAGAIN.
O_NONBLOCK disabled, n > PIPE_BUF
The write is nonatomic: the data given to write(2) may be interleaved with write(2)s by other process; the write(2) blocks until n bytes have been written.
O_NONBLOCK enabled, n > PIPE_BUF
If the pipe is full, then write(2) fails, with errno set to EAGAIN. Otherwise, from 1 to n bytes may be written (i.e., a "partial write" may occur; the caller should check the return value from write(2) to see how many bytes were actually written), and these bytes may be interleaved with writes by other processes.
 

Open File Status Flags

The only open file status flags that can be meaningfully applied to a pipe or FIFO are O_NONBLOCK and O_ASYNC.

Setting the O_ASYNC flag for the read end of a pipe causes a signal (SIGIO by default) to be generated when new input becomes available on the pipe (see fcntl(2) for details). On Linux, O_ASYNC is supported for pipes and FIFOs only since kernel 2.6.  

Portability notes

On some systems (but not Linux), pipes are bidirectional: data can be transmitted in both directions between the pipe ends. According to POSIX.1-2001, pipes only need to be unidirectional. Portable applications should avoid reliance on bidirectional pipe semantics.  

SEE ALSO

dup(2), fcntl(2), open(2), pipe(2), poll(2), select(2), socketpair(2), stat(2), mkfifo(3), epoll(7), fifo(7)  

COLOPHON

This page is part of release 3.32 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
DESCRIPTION
I/O on Pipes and FIFOs
Pipe Capacity
PIPE_BUF
Open File Status Flags
Portability notes
SEE ALSO
COLOPHON

This document was created by man2html using the manual pages.
Time: 17:32:02 GMT, October 23, 2013

4. pipe.8.man

Manpage of PIPE

PIPE

Section: Maintenance Commands (8)
Index Return to Main Contents
 

NAME

pipe - Postfix delivery to external command  

SYNOPSIS

pipe [generic Postfix daemon options] command_attributes...
 

DESCRIPTION

The pipe(8) daemon processes requests from the Postfix queue manager to deliver messages to external commands. This program expects to be run from the master(8) process manager.

Message attributes such as sender address, recipient address and next-hop host name can be specified as command-line macros that are expanded before the external command is executed.

The pipe(8) daemon updates queue files and marks recipients as finished, or it informs the queue manager that delivery should be tried again at a later time. Delivery status reports are sent to the bounce(8), defer(8) or trace(8) daemon as appropriate.  

SINGLE-RECIPIENT DELIVERY



Some destinations cannot handle more than one recipient per
delivery request. Examples are pagers or fax machines.
In addition, multi-recipient delivery is undesirable when
prepending a Delivered-to: or X-Original-To:
message header.

To prevent Postfix from sending multiple recipients per delivery request, specify

    transport_destination_recipient_limit = 1

in the Postfix main.cf file, where transport is the name in the first column of the Postfix master.cf entry for the pipe-based delivery transport.  

COMMAND ATTRIBUTE SYNTAX



The external command attributes are given in the master.cf
file at the end of a service definition.  The syntax is as follows:
chroot=pathname (optional)
Change the process root directory and working directory to the named directory. This happens before switching to the privileges specified with the user attribute, and before executing the optional directory=pathname directive. Delivery is deferred in case of failure.

This feature is available as of Postfix 2.3.

directory=pathname (optional)
Change to the named directory before executing the external command. The directory must be accessible for the user specified with the user attribute (see below). The default working directory is $queue_directory. Delivery is deferred in case of failure.

This feature is available as of Postfix 2.2.

eol=string (optional, default:
)
The output record delimiter. Typically one would use either \r
or
. The usual C-style backslash escape sequences are recognized: \a \b \f
\r \t \v \
ddd (up to three octal digits) and \\.
flags=BDFORXhqu.> (optional)
Optional message processing flags. By default, a message is copied unchanged.
B
Append a blank line at the end of each message. This is required by some mail user agents that recognize "From " lines only when preceded by a blank line.
D
Prepend a "Delivered-To: recipient" message header with the envelope recipient address. Note: for this to work, the transport_destination_recipient_limit must be 1 (see SINGLE-RECIPIENT DELIVERY above for details).

The D flag also enforces loop detection (Postfix 2.5 and later): if a message already contains a Delivered-To: header with the same recipient address, then the message is returned as undeliverable. The address comparison is case insensitive.

This feature is available as of Postfix 2.0.

F
Prepend a "From sender time_stamp" envelope header to the message content. This is expected by, for example, UUCP software.
O
Prepend an "X-Original-To: recipient" message header with the recipient address as given to Postfix. Note: for this to work, the transport_destination_recipient_limit must be 1 (see SINGLE-RECIPIENT DELIVERY above for details).

This feature is available as of Postfix 2.0.

R
Prepend a Return-Path: message header with the envelope sender address.
X
Indicate that the external command performs final delivery. This flag affects the status reported in "success" DSN (delivery status notification) messages, and changes it from "relayed" into "delivered".

This feature is available as of Postfix 2.5.

h
Fold the command-line $original_recipient and $recipient address domain part (text to the right of the right-most @ character) to lower case; fold the entire command-line $domain and $nexthop host or domain information to lower case. This is recommended for delivery via UUCP.
q
Quote white space and other special characters in the command-line $sender, $original_recipient and $recipient address localparts (text to the left of the right-most @ character), according to an 8-bit transparent version of RFC 822. This is recommended for delivery via UUCP or BSMTP.

The result is compatible with the address parsing of command-line recipients by the Postfix sendmail(1) mail submission command.

The q flag affects only entire addresses, not the partial address information from the $user, $extension or $mailbox command-line macros.

u
Fold the command-line $original_recipient and $recipient address localpart (text to the left of the right-most @ character) to lower case. This is recommended for delivery via UUCP.
.
Prepend "." to lines starting with ".". This is needed by, for example, BSMTP software.
>
Prepend ">" to lines starting with "From ". This is expected by, for example, UUCP software.
null_sender=replacement (default: MAILER-DAEMON)
Replace the null sender address (typically used for delivery status notifications) with the specified text when expanding the $sender command-line macro, and when generating a From_ or Return-Path: message header.

If the null sender replacement text is a non-empty string then it is affected by the q flag for address quoting in command-line arguments.

The null sender replacement text may be empty; this form is recommended for content filters that feed mail back into Postfix. The empty sender address is not affected by the q flag for address quoting in command-line arguments.

Caution: a null sender address is easily mis-parsed by naive software. For example, when the pipe(8) daemon executes a command such as:

    Wrong: command -f$sender -- $recipient
the command will mis-parse the -f option value when the sender address is a null string. For correct parsing, specify $sender as an argument by itself:

    Right: command -f $sender -- $recipient
This feature is available as of Postfix 2.3.
size=size_limit (optional)
Don't deliver messages that exceed this size limit (in bytes); return them to the sender instead.
user=username (required)
user=username:groupname
Execute the external command with the user ID and group ID of the specified username. The software refuses to execute commands with root privileges, or with the privileges of the mail system owner. If groupname is specified, the corresponding group ID is used instead of the group ID of username.
argv=command... (required)
The command to be executed. This must be specified as the last command attribute. The command is executed directly, i.e. without interpretation of shell meta characters by a shell command interpreter.

In the command argument vector, the following macros are recognized and replaced with corresponding information from the Postfix queue manager delivery request.

In addition to the form ${name}, the forms $name and $(name) are also recognized. Specify $$ where a single $ is wanted.

${client_address}
This macro expands to the remote client network address.

This feature is available as of Postfix 2.2.

${client_helo}
This macro expands to the remote client HELO command parameter.

This feature is available as of Postfix 2.2.

${client_hostname}
This macro expands to the remote client hostname.

This feature is available as of Postfix 2.2.

${client_port}
This macro expands to the remote client TCP port number.

This feature is available as of Postfix 2.5.

${client_protocol}
This macro expands to the remote client protocol.

This feature is available as of Postfix 2.2.

${domain}
This macro expands to the domain portion of the recipient address. For example, with an address user+foo@domain the domain is domain.

This information is modified by the h flag for case folding.

This feature is available as of Postfix 2.5.

${extension}
This macro expands to the extension part of a recipient address. For example, with an address user+foo@domain the extension is foo.

A command-line argument that contains ${extension} expands into as many command-line arguments as there are recipients.

This information is modified by the u flag for case folding.

${mailbox}
This macro expands to the complete local part of a recipient address. For example, with an address user+foo@domain the mailbox is user+foo.

A command-line argument that contains ${mailbox} expands to as many command-line arguments as there are recipients.

This information is modified by the u flag for case folding.

${nexthop}
This macro expands to the next-hop hostname.

This information is modified by the h flag for case folding.

${original_recipient}
This macro expands to the complete recipient address before any address rewriting or aliasing.

A command-line argument that contains ${original_recipient} expands to as many command-line arguments as there are recipients.

This information is modified by the hqu flags for quoting and case folding.

This feature is available as of Postfix 2.5.

${recipient}
This macro expands to the complete recipient address.

A command-line argument that contains ${recipient} expands to as many command-line arguments as there are recipients.

This information is modified by the hqu flags for quoting and case folding.

${sasl_method}
This macro expands to the name of the SASL authentication mechanism in the AUTH command when the Postfix SMTP server received the message.

This feature is available as of Postfix 2.2.

${sasl_sender}
This macro expands to the SASL sender name (i.e. the original submitter as per RFC 4954) in the MAIL FROM command when the Postfix SMTP server received the message.

This feature is available as of Postfix 2.2.

${sasl_username}
This macro expands to the SASL user name in the AUTH command when the Postfix SMTP server received the message.

This feature is available as of Postfix 2.2.

${sender}
This macro expands to the envelope sender address. By default, the null sender address expands to MAILER-DAEMON; this can be changed with the null_sender attribute, as described above.

This information is modified by the q flag for quoting.

${size}
This macro expands to Postfix's idea of the message size, which is an approximation of the size of the message as delivered.
${user}
This macro expands to the username part of a recipient address. For example, with an address user+foo@domain the username part is user.

A command-line argument that contains ${user} expands into as many command-line arguments as there are recipients.

This information is modified by the u flag for case folding.

 

STANDARDS

RFC 3463 (Enhanced status codes)
 

DIAGNOSTICS

Command exit status codes are expected to follow the conventions defined in <sysexits.h>. Exit status 0 means normal successful completion.

In the case of a non-zero exit status, a limited amount of command output is reported in an delivery status notification. When the output begins with a 4.X.X or 5.X.X enhanced status code, the status code takes precedence over the non-zero exit status (Postfix version 2.3 and later).

Problems and transactions are logged to syslogd(8). Corrupted message files are marked so that the queue manager can move them to the corrupt queue for further inspection.  

SECURITY




This program needs a dual personality 1) to access the private
Postfix queue and IPC mechanisms, and 2) to execute external
commands as the specified user. It is therefore security sensitive.
 

CONFIGURATION PARAMETERS



Changes to main.cf are picked up automatically as pipe(8)
processes run for only a limited amount of time. Use the command
"postfix reload" to speed up a change.

The text below provides only a parameter summary. See postconf(5) for more details including examples.  

RESOURCE AND RATE CONTROLS



In the text below, transport is the first field in a
master.cf entry.
transport_destination_concurrency_limit ($default_destination_concurrency_limit)
Limit the number of parallel deliveries to the same destination, for delivery via the named transport. The limit is enforced by the Postfix queue manager.
transport_destination_recipient_limit ($default_destination_recipient_limit)
Limit the number of recipients per message delivery, for delivery via the named transport. The limit is enforced by the Postfix queue manager.
transport_time_limit ($command_time_limit)
Limit the time for delivery to external command, for delivery via the named transport. The limit is enforced by the pipe delivery agent.

Postfix 2.4 and later support a suffix that specifies the time unit: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is seconds.

 

MISCELLANEOUS CONTROLS



config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf configuration files.
daemon_timeout (18000s)
How much time a Postfix daemon process may take to handle a request before it is terminated by a built-in watchdog timer.
delay_logging_resolution_limit (2)
The maximal number of digits after the decimal point when logging sub-second delay values.
export_environment (see 'postconf -d' output)
The list of environment variables that a Postfix process will export to non-Postfix processes.
ipc_timeout (3600s)
The time limit for sending or receiving information over an internal communication channel.
mail_owner (postfix)
The UNIX system account that owns the Postfix queue and most Postfix daemon processes.
max_idle (100s)
The maximum amount of time that an idle Postfix daemon process waits for an incoming connection before terminating voluntarily.
max_use (100)
The maximal number of incoming connections that a Postfix daemon process will service before terminating voluntarily.
process_id (read-only)
The process ID of a Postfix command or daemon process.
process_name (read-only)
The process name of a Postfix command or daemon process.
queue_directory (see 'postconf -d' output)
The location of the Postfix top-level queue directory.
recipient_delimiter (empty)
The separator between user names and address extensions (user+foo).
syslog_facility (mail)
The syslog facility of Postfix logging.
syslog_name (see 'postconf -d' output)
The mail system name that is prepended to the process name in syslog records, so that "smtpd" becomes, for example, "postfix/smtpd".
 

SEE ALSO

qmgr(8), queue manager
bounce(8), delivery status reports
postconf(5), configuration parameters
master(5), generic daemon options
master(8), process manager
syslogd(8), system logging
 

LICENSE



The Secure Mailer license must be distributed with this software.
 

AUTHOR(S)

Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA


 

Index

NAME
SYNOPSIS
DESCRIPTION
SINGLE-RECIPIENT DELIVERY
COMMAND ATTRIBUTE SYNTAX
STANDARDS
DIAGNOSTICS
SECURITY
CONFIGURATION PARAMETERS
RESOURCE AND RATE CONTROLS
MISCELLANEOUS CONTROLS
SEE ALSO
LICENSE
AUTHOR(S)

This document was created by man2html using the manual pages.
Time: 17:32:02 GMT, October 23, 2013

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