DragonFly On-Line Manual Pages

APPLY(1)               DragonFly General Commands Manual              APPLY(1)

NAME
     apply -- apply a command to a set of arguments

SYNOPSIS
     apply [-a c] [-d] [-#] command argument ...

DESCRIPTION
     The apply utility runs the named command on each argument argument in
     turn.

     Character sequences of the form ``%d'' in command, where `d' is a digit
     from 1 to 9, are replaced by the d'th following unused argument.  In this
     case, the largest digit number of arguments are discarded for each
     execution of command.

     The options are as follows:

     -#      Normally arguments are taken singly; the optional number -#
             specifies the number of arguments to be passed to command.  If
             the number is zero, command is run, without arguments, once for
             each argument.

             If any sequences of ``%d'' occur in command, the -# option is
             ignored.

     -a c    The use of the character `%' as a magic character may be changed
             with the -a option.

     -d      Display the commands that would have been executed, but do not
             actually execute them.

ENVIRONMENT
     The following environment variable affects the execution of apply:

     SHELL  Pathname of shell to use.  If this variable is not defined, the
            Bourne shell is used.

FILES
     /bin/sh  default shell

EXAMPLES
     apply echo *
            is similar to ls(1);
     apply -2 cmp a1 b1 a2 b2 a3 b3
            compares the `a' files to the `b' files;
     apply -0 who 1 2 3 4 5
            runs who(1) 5 times; and
     apply 'ln %1 /usr/joe' *
            links all files in the current directory to the directory
            /usr/joe.

HISTORY
     The apply command appeared in 4.2BSD.

AUTHORS
     Rob Pike

BUGS
     Shell metacharacters in command may have bizarre effects; it is best to
     enclose complicated commands in single quotes ('').

     The apply utility does not recognize multibyte characters.

DragonFly 4.9                  December 13, 2006                 DragonFly 4.9
apply(n)                     Tcl Built-In Commands                    apply(n)

______________________________________________________________________________

NAME
       apply - Apply an anonymous function

SYNOPSIS
       apply func ?arg1 arg2 ...?
______________________________________________________________________________

DESCRIPTION
       The command apply applies the function func to the arguments arg1 arg2
       ... and returns the result.

       The function func is a two element list {args body} or a three element
       list {args body namespace} (as if the list command had been used).  The
       first element args specifies the formal arguments to func. The
       specification of the formal arguments args is shared with the proc
       command, and is described in detail in the corresponding manual page.

       The contents of body are executed by the Tcl interpreter after the
       local variables corresponding to the formal arguments are given the
       values of the actual parameters arg1 arg2 ....  When body is being
       executed, variable names normally refer to local variables, which are
       created automatically when referenced and deleted when apply returns.
       One local variable is automatically created for each of the function's
       arguments.  Global variables can only be accessed by invoking the
       global command or the upvar command.  Namespace variables can only be
       accessed by invoking the variable command or the upvar command.

       The invocation of apply adds a call frame to Tcl's evaluation stack
       (the stack of frames accessed via uplevel). The execution of body
       proceeds in this call frame, in the namespace given by namespace or in
       the global namespace if none was specified. If given, namespace is
       interpreted relative to the global namespace even if its name does not
       start with "::".

       The semantics of apply can also be described by:

              proc apply {fun args} {
                  set len [llength $fun]
                  if {($len < 2) || ($len > 3)} {
                       error "can't interpret \"$fun\" as anonymous function"
                  }
                  lassign $fun argList body ns
                  set name ::$ns::[getGloballyUniqueName]
                  set body0 {
                       rename [lindex [info level 0] 0] {}
                  }
                  proc $name $argList ${body0}$body
                  set code [catch {uplevel 1 $name $args} res opt]
                  return -options $opt $res
              }

EXAMPLES
       This shows how to make a simple general command that applies a
       transformation to each element of a list.

              proc map {lambda list} {
                  set result {}
                  foreach item $list {
                      lappend result [apply $lambda $item]
                  }
                  return $result
              }
              map {x {return [string length $x]:$x}} {a bb ccc dddd}
                    -> 1:a 2:bb 3:ccc 4:dddd
              map {x {expr {$x**2 + 3*$x - 2}}} {-4 -3 -2 -1 0 1 2 3 4}
                    -> 2 -2 -4 -4 -2 2 8 16 26

       The apply command is also useful for defining callbacks for use in the
       trace command:

              set vbl "123abc"
              trace add variable vbl write {apply {{v1 v2 op} {
                  upvar 1 $v1 v
                  puts "updated variable to \"$v\""
              }}}
              set vbl 123
              set vbl abc

SEE ALSO
       proc(n), uplevel(n)

KEYWORDS
       anonymous function, argument, lambda, procedure,

Tcl                                                                   apply(n)