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RedHat 9 (Linux i386) - man page for open (redhat section n)

open(n) 			      Tcl Built-In Commands				  open(n)

_________________________________________________________________________________________________

NAME
       open - Open a file-based or command pipeline channel

SYNOPSIS
       open fileName
       open fileName access
       open fileName access permissions
_________________________________________________________________

DESCRIPTION
       This  command opens a file, serial port, or command pipeline and returns a channel identi- |
       fier that may be used in future invocations of commands like read, puts,  and  close.   If
       the first character of fileName is not | then the command opens a file: fileName gives the
       name of the file to open, and it must conform to the conventions described in the filename
       manual entry.

       The access argument, if present, indicates the way in which the file (or command pipeline)
       is to be accessed.  In the first form access may have any of the following values:

       r	      Open the file for reading only; the file must already exist.  This  is  the
		      default value if access is not specified.

       r+	      Open the file for both reading and writing; the file must already exist.

       w	      Open  the  file for writing only.  Truncate it if it exists.  If it doesn't
		      exist, create a new file.

       w+	      Open the file for reading and writing.  Truncate it if it  exists.   If  it
		      doesn't exist, create a new file.

       a	      Open  the  file  for writing only.  If the file doesn't exist, create a new
		      empty file.  Set the initial access position  to the end of the file.

       a+	      Open the file for reading and writing.  If the file doesn't exist, create a
		      new empty file.  Set the initial access position	to the end of the file.

       In  the second form, access consists of a list of any of the following flags, all of which
       have the standard POSIX meanings.  One of the flags must be either RDONLY, WRONLY or RDWR.

       RDONLY	      Open the file for reading only.

       WRONLY	      Open the file for writing only.

       RDWR	      Open the file for both reading and writing.

       APPEND	      Set the file pointer to the end of the file prior to each write.

       CREAT	      Create the file if it doesn't already exist (without this  flag  it  is  an
		      error for the file not to exist).

       EXCL	      If  CREAT  is  also  specified,  an  error  is returned if the file already
		      exists.

       NOCTTY	      If the file is a terminal device, this flag prevents the file from becoming
		      the controlling terminal of the process.

       NONBLOCK       Prevents	the process from blocking while opening the file, and possibly in
		      subsequent I/O operations.  The exact behavior of this flag is system-  and
		      device-dependent;  its use is discouraged (it is better to use the fconfig-
		      ure command to put a file in nonblocking mode).  For details refer to  your
		      system documentation on the open system call's O_NONBLOCK flag.

       TRUNC	      If the file exists it is truncated to zero length.

       If  a  new  file is created as part of opening it, permissions (an integer) is used to set
       the permissions for the new file in conjunction with  the  process's  file  mode  creation
       mask.  Permissions defaults to 0666.

       Note  that  if you are going to be reading or writing binary data from the channel created |
       by this command, you should use the fconfigure command to change the  -translation  option |
       of  the channel to binary before transferring any binary data.  This is in contrast to the |
       ``b'' character passed as part of the equivalent of the access parameter to some  versions |
       of the C library fopen() function.

COMMAND PIPELINES
       If  the first character of fileName is ``|'' then the remaining characters of fileName are
       treated as a list of arguments that describe a command pipeline to  invoke,  in	the  same
       style  as  the  arguments for exec.  In this case, the channel identifier returned by open
       may be used to write to the command's input pipe or read from its output  pipe,	depending
       on  the	value  of access.  If write-only access is used (e.g. access is w), then standard
       output for the pipeline is directed to the current standard output  unless  overridden  by
       the command.  If read-only access is used (e.g. access is r), standard input for the pipe-
       line is taken from the current standard input unless overridden by the command.

SERIAL COMMUNICATIONS
       If fileName refers to a serial port, then the specified serial port is opened and initial- |
       ized  in a platform-dependent manner.  Acceptable values for the fileName to use to open a |
       serial port are described in the PORTABILITY ISSUES section.				  |

CONFIGURATION OPTIONS										  |
       The fconfigure command can be used to query and set the following configuration option for |
       open serial ports:									  |

       -mode baud,parity,data,stop								  |
	      This  option is a set of 4 comma-separated values: the baud rate, parity, number of |
	      data bits, and number of stop bits for this serial port.	The baud rate is a simple |
	      integer  that  specifies the connection speed.  Parity is one of the following let- |
	      ters: n, o, e, m, s;  respectively  signifying  the  parity  options  of	``none'', |
	      ``odd'',	``even'',  ``mark'',  or  ``space''.  Data is the number of data bits and |
	      should be an integer from 5 to 8, while stop is the number of stop bits and  should |
	      be the integer 1 or 2.								  |

       -pollinterval msec									  |
	      This option, available only on Windows for serial ports, is used to set the maximum |
	      time between polling for fileevents.  This affects the time interval between check- |
	      ing  for	events	throughout  the Tcl interpreter (the smallest value always wins). |
	      Use this option only if you want to poll the serial port more often  than  10  msec |
	      (the default).									  |

       -lasterror										  |
	      This  option is available only on Windows for serial ports, and is query only (will |
	      only be reported when directly requested).   In  case  of  a  serial  communication |
	      error,  read  or	puts returns a general Tcl file I/O error.  fconfigure -lasterror |
	      can be called to get a list of error details (e.g. FRAME RXOVER).

PORTABILITY ISSUES										  |
       Windows (all versions)									  |
	      Valid values for fileName to open a serial port are of the form comX:, where X is a |
	      number, generally from 1 to 4.  This notation only works for serial ports from 1 to |
	      9, if the system happens to have more than four.	An attempt to open a serial  port |
	      that does not exist or has a number greater than 9 will fail.  An alternate form of |
	      opening serial ports is to use the filename \\.\comX, where X is	any  number  that |
	      corresponds  to  a serial port; please note that this method is considerably slower |
	      on Windows 95 and Windows 98.							  |

       Windows NT										  |
	      When running Tcl interactively, there may be some strange interactions between  the |
	      real console, if one is present, and a command pipeline that uses standard input or |
	      output.  If a command pipeline is opened for reading, some of the lines entered  at |
	      the  console  will be sent to the command pipeline and some will be sent to the Tcl |
	      evaluator.  If a command pipeline is opened for writing,	keystrokes  entered  into |
	      the  console  are  not  visible until the the pipe is closed.  This behavior occurs |
	      whether the command pipeline is executing 16-bit	or  32-bit  applications.   These |
	      problems	only  occur  because both Tcl and the child application are competing for |
	      the console at the same time.  If the command pipeline is started from a script, so |
	      that  Tcl  is  not  accessing  the console, or if the command pipeline does not use |
	      standard input or output, but is redirected from or to a file, then the above prob- |
	      lems do not occur.								  |

       Windows 95										  |
	      A command pipeline that executes a 16-bit DOS application cannot be opened for both |
	      reading and writing, since 16-bit DOS applications that receive standard input from |
	      a  pipe  and  send  standard output to a pipe run synchronously.	Command pipelines |
	      that do not execute 16-bit DOS applications run asynchronously and  can  be  opened |
	      for both reading and writing.							  |

	      When  running Tcl interactively, there may be some strange interactions between the |
	      real console, if one is present, and a command pipeline that uses standard input or |
	      output.	If  a  command	pipeline is opened for reading from a 32-bit application, |
	      some of the keystrokes entered at the console will be sent to the command  pipeline |
	      and  some  will  be sent to the Tcl evaluator.  If a command pipeline is opened for |
	      writing to a 32-bit application, no output is visible on the console until the  the |
	      pipe  is closed.	These problems only occur because both Tcl and the child applica- |
	      tion are competing for the console at the same time.  If the  command  pipeline  is |
	      started  from a script, so that Tcl is not accessing the console, or if the command |
	      pipeline does not use standard input or output, but is  redirected  from	or  to	a |
	      file, then the above problems do not occur.					  |

	      Whether  or  not	Tcl is running interactively, if a command pipeline is opened for |
	      reading from a 16-bit DOS application, the call to open will not return until  end- |
	      of-file  has  been received from the command pipeline's standard output.	If a com- |
	      mand pipeline is opened for writing to a 16-bit DOS application, no  data  will  be |
	      sent  to	the command pipeline's standard output until the pipe is actually closed. |
	      This problem occurs because 16-bit  DOS  applications  are  run  synchronously,  as |
	      described above.									  |

       Macintosh										  |
	      Opening a serial port is not currently implemented under Macintosh.		  |

	      Opening  a command pipeline is not supported under Macintosh, since applications do |
	      not support the concept of standard input or output.				  |

       Unix											  |
	      Valid values for fileName  to  open  a  serial  port  are  generally  of	the  form |
	      /dev/ttyX, where X is a or b, but the name of any pseudo-file that maps to a serial |
	      port may be used. 								  |

	      When running Tcl interactively, there may be some strange interactions between  the |
	      console,	if one is present, and a command pipeline that uses standard input.  If a |
	      command pipeline is opened for reading, some of the lines entered  at  the  console |
	      will  be	sent  to the command pipeline and some will be sent to the Tcl evaluator. |
	      This problem only occurs because both Tcl and the child application  are	competing |
	      for  the	console  at  the  same	time.	If the command pipeline is started from a |
	      script, so that Tcl is not accessing the console, or if the command  pipeline  does |
	      not  use standard input, but is redirected from a file, then the above problem does |
	      not occur.									  |

       See the PORTABILITY ISSUES section of the exec command for additional information not spe- |
       cific to command pipelines about executing applications on the various platforms 	  |

SEE ALSO											  |
       file(n),   close(n),  filename(n),  fconfigure(n),  gets(n),  read(n),  puts(n),  exec(n), |
       fopen(1) 										  |

KEYWORDS											  |
       access mode, append, create, file, non-blocking,  open,	permissions,  pipeline,  process, |
       serial											  |

Tcl					       7.6					  open(n)


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