Command Reference2.  FPGA Express Shell Commands         redirect



_N_A_M_E
          redirect       Redirects the output of a command to a
                         file.


SYNTAX
          string redirect [-append] _f_i_l_e__n_a_m_e {_c_o_m_m_a_n_d}

          string    _f_i_l_e__n_a_m_e
          string    _c_o_m_m_a_n_d


ARGUMENTS
          -append        Appends the output to _f_i_l_e__n_a_m_e.


          _f_i_l_e__n_a_m_e      Indicates the file to which to redirect
                         output.


          _c_o_m_m_a_n_d        The command to execute. Intermediate
                         output from this command, as well as the
                         result of the command, will be
                         redirected to _f_i_l_e__n_a_m_e.



DESCRIPTION
          The redirect command performs the same function as the
          traditional unix-style redirection operators > and >>.
          The _c_o_m_m_a_n_d must be rigidly quoted (that is, enclosed
          in curly braces) in order for the operation to succeed.
          It must not be constructed as a nested command.

          The result of a redirect command which does not
          generate a Tcl error is the empty string.  Screen
          output occurs only if errors occurred during execution
          of the _c_o_m_m_a_n_d (other than opening the redirect file).
          When errors occur, a summary message is outpt.  See the
          examples.

          Although the result of a successful redirect command is
          the empty string, it is still possible to get and use
          the result of the command that you redirected.
          Construct a set command in which you set a variable to
          the result of your command. Then, redirect the set
          command.  The variable holds the result of your
          command.  See the examples.

          The redirect command is much more flexible that
          traditional unix redirection operators.  With redirect,
          you can redirect multiple commands or an entire script.



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redirect        2.  FPGA Express Shell Commands Command Reference



          See the examples for an example of how to construct
          such a command.

          Note that the builtin Tcl command puts does not respond
          to output redirection of any kind. Use the builtin echo
          command instead.

















































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Command Reference2.  FPGA Express Shell Commands         redirect



EXAMPLES
          In the following example, the output of the plus
          procedure is redirected.  The echoed string and the
          result of the plus operation is in the output file.
          Notice that the result was not echoed to the screen.

               prompt> proc plus {a b} {echo "In plus" ; return [expr $a + $b]}
               prompt> redirect p.out {plus 12 13}
               prompt> exec cat p.out
               In plus
               25


          In this example, a typo in the command created an error
          condition.  The error message indicates that you can
          use error_info to trace the error, but you should first
          check the output file.

               prompt> redirect p.out {plus2 12 13}
               Error: Errors detected during redirect
                       Use error_info for more info. (CMD-013)
               prompt> exec cat p.out
               Error: unknown command 'plus2' (CMD-005)


          In this example, we explore the usage of results from
          redirected commands.  Since the result of  redirect for
          a command which does not generate a Tcl error is the
          empty string, use the set command to trap the result of
          the command.  For example, assume that there is a
          command to read a file which has a result of "1" if it
          succeeds, and "0" if it fails.  If you redirect only
          the command, there is no way to know if it succeeded.

               redirect p.out { read_a_file "a.txt" }
               # Now what?  How can I redirect and use the result?


          But if you set a variable to the result, then it is
          possible to use that result in a conditional
          expression, etc.

               redirect p.out { set rres [read_a_file "a.txt"] }
               if { $rres == 1 } {
                 echo "Read ok!"
               }


          The redirect command is not limited to redirection of a
          single command.  You can redirect entire blocks of a
          script with a single redirect command.  This simple
          example with echo demonstrates this feature:



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redirect        2.  FPGA Express Shell Commands Command Reference



               prompt> redirect p.out {
               ?         echo -n "Hello "
               ?         echo "world"
               ?       }
               prompt> exec cat p.out
               Hello world
               prompt>



SEE ALSO
          echo(2), _e_r_r_o_r__i_n_f_o(2), _s_e_t(2).











































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