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foreach(n) [osx man page]

foreach(n)						       Tcl Built-In Commands							foreach(n)


foreach - Iterate over all elements in one or more lists SYNOPSIS
foreach varname list body foreach varlist1 list1 ?varlist2 list2 ...? body _________________________________________________________________ DESCRIPTION
The foreach command implements a loop where the loop variable(s) take on values from one or more lists. In the simplest case there is one loop variable, varname, and one list, list, that is a list of values to assign to varname. The body argument is a Tcl script. For each element of list (in order from first to last), foreach assigns the contents of the element to varname as if the lindex command had been used to extract the element, then calls the Tcl interpreter to execute body. In the general case there can be more than one value list (e.g., list1 and list2), and each value list can be associated with a list of loop variables (e.g., varlist1 and varlist2). During each iteration of the loop the variables of each varlist are assigned consecutive values from the corresponding list. Values in each list are used in order from first to last, and each value is used exactly once. The total number of loop iterations is large enough to use up all the values from all the value lists. If a value list does not contain enough elements for each of its loop variables in each iteration, empty values are used for the missing elements. The break and continue statements may be invoked inside body, with the same effect as in the for command. Foreach returns an empty string. EXAMPLES
This loop prints every value in a list together with the square and cube of the value: set values {1 3 5 7 2 4 6 8} ;# Odd numbers first, for fun! puts "Value Square Cube" ;# Neat-looking header foreach x $values { ;# Now loop and print... puts " $x [expr {$x**2}] [expr {$x**3}]" } The following loop uses i and j as loop variables to iterate over pairs of elements of a single list. set x {} foreach {i j} {a b c d e f} { lappend x $j $i } # The value of x is "b a d c f e" # There are 3 iterations of the loop. The next loop uses i and j to iterate over two lists in parallel. set x {} foreach i {a b c} j {d e f g} { lappend x $i $j } # The value of x is "a d b e c f {} g" # There are 4 iterations of the loop. The two forms are combined in the following example. set x {} foreach i {a b c} {j k} {d e f g} { lappend x $i $j $k } # The value of x is "a d e b f g c {} {}" # There are 3 iterations of the loop. SEE ALSO
for(n), while(n), break(n), continue(n) KEYWORDS
foreach, iteration, list, looping Tcl foreach(n)

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for(n)							       Tcl Built-In Commands							    for(n)


for - ``For'' loop SYNOPSIS
for start test next body _________________________________________________________________ DESCRIPTION
For is a looping command, similar in structure to the C for statement. The start, next, and body arguments must be Tcl command strings, and test is an expression string. The for command first invokes the Tcl interpreter to execute start. Then it repeatedly evaluates test as an expression; if the result is non-zero it invokes the Tcl interpreter on body, then invokes the Tcl interpreter on next, then repeats the loop. The command terminates when test evaluates to 0. If a continue command is invoked within body then any remaining commands in the current execution of body are skipped; processing continues by invoking the Tcl interpreter on next, then evaluating test, and so on. If a break command is invoked within body or next, then the for command will return immediately. The operation of break and continue are similar to the corresponding statements in C. For returns an empty string. Note: test should almost always be enclosed in braces. If not, variable substitutions will be made before the for command starts execut- ing, which means that variable changes made by the loop body will not be considered in the expression. This is likely to result in an infinite loop. If test is enclosed in braces, variable substitutions are delayed until the expression is evaluated (before each loop iter- ation), so changes in the variables will be visible. For an example, try the following script with and without the braces around $x<10: for {set x 0} {$x<10} {incr x} { puts "x is $x" } SEE ALSO
break, continue, foreach, while KEYWORDS
for, iteration, looping Tcl for(n)
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