This command is part of the TclX package.

for_file var filename code

This command implements a loop over the contents of a file. For each line in filename, it sets var to the line and executes code.

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Here's how to redo it in pure-Tcl:

 proc for_file {varName filename body} {
    upvar 1 $varName var
    set fp [open $filename]
    while {[gets $fp var]>=0} {
       uplevel 1 $body
    }
    close $fp
 } ;#

break and continue support would need some extra action, compare do...until in Tcl.

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