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


apply -- apply a command to a set of arguments


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


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.


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.


/bin/sh default shell


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.


The apply command appeared in 4.2BSD.


Rob Pike


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) ______________________________________________________________________________


apply - Apply an anonymous function


apply func ?arg1 arg2 ...? ______________________________________________________________________________


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 }


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


proc(n), uplevel(n)


anonymous function, argument, lambda, procedure, Tcl apply(n)

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