'''S'''tream '''Ed'''itor

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
[http://www.grymoire.com/Unix/Sed.html#uh-0].

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.

One reason Tcl'ers encounter '''sed''' is that [autoconf] and autoconf-generated build scripts makes heavy use of sed to mangle text.
----
 $ 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 $f}
 proc < {filename}     {set f [open $filename]; return [read $f][close $f]}
----
[RS] 2006-09-05: Playing around, waiting for a longish run to complete:
 proc sed {script input} {
    set sep [string index $script 1]
    foreach {cmd from to flag} [split $script $sep] break
    if {$cmd ne "s"} {error "not yet implemented"}
    set cmd regsub
    if {$flag eq "g"} {lappend cmd -all}
    lappend cmd $from $input $to
    eval $cmd
 }
Testing:
 sed s-foo-bar "A foolish idea for fools"
 A barlish idea for fools
 % sed s/foo/bar/g "A foolish idea for fools"
 A barlish idea for barls

Add to it to make it come closer to the real thing:^)

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