Filters

$ cat q.tcl                                                                                                              
# Filters

package require tov

set reader  [::tov::FileReader new in.txt]
set filter1 [::tov::FilterDoer new]
set filter2 [::tov::FilterDoer new]
set writer  [[::tov::FileWriter new out.txt] cascade { configure -buffering none ` yourself }]

$reader  sender [format {%s value $value} $filter1]  ;# One way to do it.
$filter1 sender "$filter2 value \$value"             ;# Another way. Neither are pretty.

$filter1 calculator {string toupper $value}

$filter2 cascade [format {
          calculator {regsub -all {\.} $value "!"}
        ` sender {%s value $value}
} $writer]; # Meh for usability.

$reader value -1 ;# Go.

$reader  destroy
$filter1 destroy
$filter2 destroy
$writer  destroy

# EOF

$ cat in.txt; tclsh8.6 q.tcl; cat out.txt
A Tcl script is a string containing one or more commands.
A TCL SCRIPT IS A STRING CONTAINING ONE OR MORE COMMANDS!