Go to main content

man pages section 1: User Commands

Exit Print View

Updated: Thursday, June 13, 2019
 
 

open (1t)

Name

open - based or command pipeline channel

Synopsis

open fileName
open fileName access
open fileName access permissions

Description

open(1t)                     Tcl Built-In Commands                    open(1t)



______________________________________________________________________________

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 identifier 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 speci-
                      fied.

       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 does not exist, create a new file.

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

       a              Open  the  file  for writing only.  If the file does not
                      exist, create a new empty file.  Set the file pointer to
                      the end of the file prior to each write.

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

       All  of the legal access values above may have the character b added as
       the second or third character in the value to indicate that the  opened
       channel  should  be  configured  as if with the fconfigure -translation
       binary option, making the channel suitable for reading  or  writing  of
       binary data.

       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.

       BINARY         Configure  the  opened  channel  with  the  -translation
                      binary option.

       CREAT          Create  the  file  if it does not 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-depen-
                      dent;  its use is discouraged (it is better to  use  the
                      fconfigure  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 inte-
       ger) is used to set the permissions for the  new  file  in  conjunction
       with  the  process's  file mode creation mask.  Permissions defaults to
       0666.

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 pipeline is  taken
       from  the current standard input unless overridden by the command.  The
       id of the spawned process is accessible through the pid command,  using
       the channel id returned by open as argument.

       If  the  command (or one of the commands) executed in the command pipe-
       line returns an error (according to the  definition  in  exec),  a  Tcl
       error is generated when close is called on the channel unless the pipe-
       line is in non-blocking mode then no exit status is returned (a  silent
       close with -blocking 0).

       It is often useful to use the fileevent command with pipelines so other
       processing may happen at the same time as running the  command  in  the
       background.

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

       The fconfigure command can be used to query and set additional configu-
       ration options specific to serial ports (where supported):

       -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  letters:
              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.

       -handshake type
              (Windows and Unix). This option is used to setup automatic hand-
              shake control. Note that not all handshake types maybe supported
              by your operating system. The type  parameter  is  case-indepen-
              dent.

              If  type  is  none  then  any handshake is switched off.  rtscts
              activates hardware handshake.  Hardware  handshake  signals  are
              described  below.   For software handshake xonxoff the handshake
              characters can be redefined with -xchar.  An additional hardware
              handshake  dtrdsr  is available only under Windows.  There is no
              default handshake configuration, the initial  value  depends  on
              your operating system settings.  The -handshake option cannot be
              queried.

       -queue (Windows and Unix). The -queue option can only be  queried.   It
              returns  a  list of two integers representing the current number
              of bytes in the input and output queue respectively.

       -timeout msec
              (Windows and Unix). This option is used to set the  timeout  for
              blocking  read  operations.  It  specifies  the maximum interval
              between the reception of two bytes in  milliseconds.   For  Unix
              systems  the  granularity  is  100  milliseconds.   The -timeout
              option does not affect write operations  or  nonblocking  reads.
              This option cannot be queried.

       -ttycontrol {signal boolean signal boolean ...}
              (Windows  and  Unix). This option is used to setup the handshake
              output lines (see below) permanently or to send a BREAK over the
              serial line.  The signal names are case-independent.  {RTS 1 DTR
              0} sets the RTS output to high and the DTR output to  low.   The
              BREAK  condition (see below) is enabled and disabled with {BREAK
              1} and {BREAK 0} respectively.  It is not a good idea to  change
              the  RTS  (or  DTR) signal with active hardware handshake rtscts
              (or dtrdsr).  The  result  is  unpredictable.   The  -ttycontrol
              option cannot be queried.

       -ttystatus
              (Windows  and  Unix). The -ttystatus option can only be queried.
              It returns the current modem status and handshake input  signals
              (see  below).  The result is a list of signal,value pairs with a
              fixed order, e.g. {CTS 1 DSR 0 RING 1 DCD 0}.  The signal  names
              are returned upper case.

       -xchar {xonChar xoffChar}
              (Windows  and  Unix). This option is used to query or change the
              software handshake characters.  Normally  the  operating  system
              default  should  be  DC1  (0x11) and DC3 (0x13) representing the
              ASCII standard XON and XOFF characters.

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

       -sysbuffer inSize

       -sysbuffer {inSize outSize}
              (Windows  only).  This option is used to change the size of Win-
              dows system buffers for a serial channel. Especially  at  higher
              communication  rates the default input buffer size of 4096 bytes
              can overrun for latent systems. The  first  form  specifies  the
              input buffer size, in the second form both input and output buf-
              fers are defined.

       -lasterror
              (Windows only). This option is query only.  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.   See  below  for  an explanation of the various
              error codes.

SERIAL PORT SIGNALS
       RS-232 is the most commonly  used  standard  electrical  interface  for
       serial  communications.  A  negative  voltage (-3V..-12V) define a mark
       (on=1) bit and a positive voltage (+3..+12V) define a space (off=0) bit
       (RS-232C).  The following signals are specified for incoming and outgo-
       ing data, status lines and handshaking. Here we  are  using  the  terms
       workstation  for  your  computer  and  modem  for  the external device,
       because some signal names (DCD, RI) come from modems.  Of  course  your
       external device may use these signal lines for other purposes.

       TXD(output)
              Transmitted Data: Outgoing serial data.

       RXD(input)
              Received Data:Incoming serial data.

       RTS(output)
              Request  To Send: This hardware handshake line informs the modem
              that your workstation is ready to receive data. Your workstation
              may  automatically  reset this signal to indicate that the input
              buffer is full.

       CTS(input)
              Clear To Send: The complement to RTS. Indicates that  the  modem
              is ready to receive data.

       DTR(output)
              Data  Terminal Ready: This signal tells the modem that the work-
              station is ready to establish a link. DTR is often enabled auto-
              matically whenever a serial port is opened.

       DSR(input)
              Data  Set  Ready:  The  complement to DTR. Tells the workstation
              that the modem is ready to establish a link.

       DCD(input)
              Data Carrier Detect: This  line  becomes  active  when  a  modem
              detects a "Carrier" signal.

       RI(input)
              Ring  Indicator:  Goes active when the modem detects an incoming
              call.

       BREAK  A BREAK condition is not a hardware signal line, but  a  logical
              zero  on the TXD or RXD lines for a long period of time, usually
              250 to 500 milliseconds.  Normally a receive  or  transmit  data
              signal stays at the mark (on=1) voltage until the next character
              is transferred. A BREAK is sometimes used to reset the  communi-
              cations  line  or  change  the  operating mode of communications
              hardware.

ERROR CODES (Windows only)
       A lot of different errors may occur during serial  read  operations  or
       during  event  polling in background. The external device may have been
       switched off, the data lines may be noisy, system buffers  may  overrun
       or  your  mode  settings may be wrong.  That is why a reliable software
       should always catch serial read operations.  In cases of an  error  Tcl
       returns  a general file I/O error.  Then fconfigure -lasterror may help
       to locate the problem.  The following error codes may be returned.

       RXOVER    Windows input buffer overrun. The data comes faster than your
                 scripts reads it or your system is overloaded. Use fconfigure
                 -sysbuffer to avoid a temporary bottleneck and/or  make  your
                 script faster.

       TXFULL    Windows  output  buffer  overrun.  Complement to RXOVER. This
                 error should practically not happen, because Tcl cares  about
                 the output buffer status.

       OVERRUN   UART  buffer  overrun  (hardware)  with  data lost.  The data
                 comes faster than the system driver receives it.  Check  your
                 advanced serial port settings to enable the FIFO (16550) buf-
                 fer and/or setup a lower(1) interrupt threshold value.

       RXPARITY  A parity error has been detected by your UART.  Wrong  parity
                 settings with fconfigure -mode or a noisy data line (RXD) may
                 cause this error.

       FRAME     A stop-bit error has been detected by your UART.  Wrong  mode
                 settings with fconfigure -mode or a noisy data line (RXD) may
                 cause this error.

       BREAK     A BREAK condition has been detected by your UART (see above).

PORTABILITY ISSUES
       Windows
              Valid values for fileName to open a serial port are of the  form
              comX, where X is a number, generally from 1 to 9.  A legacy form
              accepted as well is comX:. This notation only works  for  serial
              ports  from  1 to 9.  An attempt to open a serial port that does
              not exist or has a number greater than 9 will fail.   An  alter-
              nate  form  of  opening  serial  ports  is  to  use the filename
              //./comX, where X is any number that  corresponds  to  a  serial
              port.

              When running Tcl interactively, there may be some strange inter-
              actions between the real console, if one is present, and a  com-
              mand  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 pipe is closed.  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 com-
              mand pipeline does not use standard  input  or  output,  but  is
              redirected  from  or  to  a file, then the above problems do not
              occur.

       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.   Advanced
              configuration  options  are only supported for serial ports when
              Tcl is built to use the POSIX serial interface.

              When running Tcl interactively, there may be some strange inter-
              actions  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  pipe-
              line 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 specific to command pipelines about executing applica-
       tions on the various platforms

EXAMPLE
       Open a command pipeline and catch any errors:

              set fl [open "| ls this_file_does_not_exist"]
              set data [read $fl]
              if {[catch {close $fl} err]} {
                  puts "ls command failed: $err"
              }


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       +---------------+------------------+
       |ATTRIBUTE TYPE | ATTRIBUTE VALUE  |
       +---------------+------------------+
       |Availability   | runtime/tcl-8    |
       +---------------+------------------+
       |Stability      | Uncommitted      |
       +---------------+------------------+
SEE ALSO
       file(n),  close(n),  filename(n),  fconfigure(n),   gets(n),   read(n),
       puts(n), exec(n), pid(n), fopen(3)

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



NOTES
       This    software    was    built    from    source     available     at
       https://github.com/oracle/solaris-userland.    The  original  community
       source was downloaded from  http://prdownloads.sourceforge.net/tcl/tcl-
       core8.6.7-src.tar.gz

       Further information about this software can be found on the open source
       community website at https://www.tcl.tk/.



Tcl                                   8.3                             open(1t)