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OpenSolaris 2009.06 - man page for eval (opensolaris section 1)

exec(1) 				  User Commands 				  exec(1)

NAME
       exec, eval, source - shell built-in functions to execute other commands

SYNOPSIS
   sh
       exec [argument]...

       eval [argument]...

   csh
       exec command

       eval argument...

       source [-h] name

   ksh
       *exec [argument]...

       *eval [argument]...

   ksh93
       +exec [-c] [-a name] [command [argument ... ]]

       +eval [argument]...

DESCRIPTION
   sh
       The  exec  command  specified  by the arguments is executed in place of this shell without
       creating a new process. Input/output arguments and appear and, if no other  arguments  are
       specified, cause the shell input/output to be modified.

       The  arguments  to the eval built-in are read as input to the shell and the resulting com-
       mand(s) executed.

   csh
       exec executes command in place of the current shell, which terminates.

       eval reads its arguments as input to the shell and executes the resulting command(s). This
       is usually used to execute commands generated as the result of command or variable substi-
       tution.

       source reads commands from name. source commands can be nested, but if they are nested too
       deeply  the shell can run out of file descriptors. An error in a sourced file at any level
       terminates all nested source commands.

       -h    Place commands from the file name on the history list without executing them.

   ksh
       With the exec built-in, if arg is specified, the command specified  by  the  arguments  is
       executed in place of this shell without creating a new process. Input/output arguments can
       appear and affect the current process. If no arguments are specified the  effect  of  this
       command	is to modify file descriptors as prescribed by the input/output redirection list.
       In this case, any file descriptor numbers greater than 2 that are opened with this  mecha-
       nism are closed when invoking another program.

       The  arguments  to  eval  are read as input to the shell and the resulting command(s) exe-
       cuted.

       On this man page, ksh(1) commands that are preceded  by	one  or  two  *  (asterisks)  are
       treated specially in the following ways:

	   1.	  Variable  assignment lists preceding the command remain in effect when the com-
		  mand completes.

	   2.	  I/O redirections are processed after variable assignments.

	   3.	  Errors cause a script that contains them to abort.

	   4.	  Words, following a command preceded by ** that are in the format of a  variable
		  assignment,  are  expanded  with  the same rules as a variable assignment. This
		  means that tilde substitution is performed after the = sign and word	splitting
		  and file name generation are not performed.

   ksh93
       exec  is  a special built-in command that can be used to manipulate file descriptors or to
       replace the current shell with a new command.

       If command is specified, then the current shell process is replaced by command rather than
       running	command  and  waiting for it to complete. There is no need to use exec to enhance
       performance since the shell implicitly uses the exec mechanism internally whenever  possi-
       ble.

       If  no  operands  are specified, exec can be used to open or close files, or to manipulate
       file descriptors from 0 to 9 in the current shell environment using the standard redirect-
       ion mechanism available with all commands. The close-on-exec flags is set on file descrip-
       tor numbers greater than 2 that are opened this way so that they are closed  when  another
       program is invoked.

       Because	exec is a special command, any failure causes the script that invokes it to exit.
       This can be prevented by invoking exec from the command	utility.

       exec cannot be invoked from a restricted shell to create files or to open a file for writ-
       ing or appending.

       eval  is  a  shell special built-in command that constructs a command by concatenating the
       arguments together, separating each with a space. The resulting string is taken	as  input
       to  the	shell and evaluated in the current environment. command words are expanded twice,
       once to construct argument, and again when the shell executes the constructed command.  It
       is not an error if argument is not specified.

       On  this manual page, ksh93 commands that are preceded by one or two + symbols are special
       built-in commands and are treated specially in the following ways:

	   1.	  Variable assignment lists preceding the command remain in effect when the  com-
		  mand completes.

	   2.	  I/O redirections are processed after variable assignments.

	   3.	  Errors cause a script that contains them to abort.

	   4.	  They are not valid function names.

	   5.	  Words  following  a command preceded by ++ that are in the format of a variable
		  assignment are expanded with the same rules  as  a  variable	assignment.  This
		  means that tilde substitution is performed after the = sign and field splitting
		  and file name generation are not performed.

OPTIONS
   ksh93
       The following options are supported by ksh93 exec:

       -a name	  argv[0] is set to name for command.

       -c	  Clear all environment variables before executions except  variable  assignments
		  that are part of the current exec command.

EXIT STATUS
   ksh
       The following exit values are returned by exec:

       0	Successful completion.

       1-125	A redirection error occurred.

       127	command was not found.

       126	command was found, but it is not an executable utility.

   ksh93
       The  following  exit  values  are returned by exec. If command is specified, exec does not
       return.

       0     Successful completion. All I/O redirections were successful.

       >0    An error occurred.

       The following exit values are returned by eval:

       If argument is not specified, the exit status is 0. Otherwise, it is the  exit  status  of
       the command defined by the argument operands.

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO
       csh(1), ksh(1), ksh93(1), sh(1), attributes(5)

SunOS 5.11				    8 Apr 2008					  exec(1)


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