Richard Suchenwirth 2003-07-09 - After having written the following code repeatedly, I just declare it to be an idiom. The filter functionality is frequently seen on Unix (and even DOS) tools, and I think was published in the Software Tools book:
Such tools (grep, sed, awk, sort, ...) can easily be combined ("glued") in pipes to do powerful things. A little framework for Tcl scripts with the filter functionality:
set about "usage: myFilter ?file...?
Does something meaningful with the specified fiules, or stdin.
"
#-- This handler contains the real functionality for one stream (or file)
proc myHandler channel {
...
}
#-- This prevents lengthy errors if a filter|more is terminated with 'q'
proc puts! string {catch {puts stdout $string}}
if {[lsearch $argv "--help"]>=0} {puts $about; exit}
if {[llength $argv]==0} {
puts! [myHandler stdin]
} else {
foreach file $argv {
set fp [open $file]
puts! [myHandler $fp]
close $fp
}
}