Stream Editor
A program that parses files or standard input, changes it according to a given set of rules, mostly based on Regular Expressions, and sends the new data to standard output. Unbelievably fast.
Erik Pemente keeps a very good amount of info and links in this page: http://www.student.northpark.edu/pemente/sed/ A spirited introduction to sed programming appears here [L1 ].
There is a page dedicated to the Tcl's implementation of Regular Expressions on this wiki. Tcl uses ARE. sed uses Basic and Extended Regular Expressions only.
$ sed s/foo/bar/ < infile > outfile
can in Tcl be substituted either with regsub or, when like in this case, no regular expression features are needed, with string map:
% > outfile [regsub -all foo [< infile] bar]
resp.
% > outfile [string map {foo bar} [< infile]]where
proc > {filename str} {set f [open $filename w]; puts $f $str; close $w}
proc < filename {set f [open $filename]; return [read $f][close $f]}