« Square-Wheeled Bicycle | Main | Origin of the Phrase "Proudly Serving My Corporate Masters" »
July 26, 2005
switch -file, and Regex Hooha
Here's another cool thing in Monad. You know in Perl you have the<> syntax for ripping through files: you get code sequences like:
open FH,"filename";
while (<FH>)
if (some-regular-expression) {
# code to handle lines that match
}
elsif (another-regular-expression) {
# code to handle lines that match
}
# etc.
}
close FH;
Well, Monad has a -file option on the switch statement which can do similar things, especially when combined with the -regex option on switch (which tells it to do regex instead of exact matching):
switch -file "filename" -regex {
"some-regular-expression" {
# code to handle lines that match
}
"another-regular-expression" {
# code to handle lines that match
}
# etc.
}
If you want to run through a bunch of files, then you can enclose the switch in a foreach. Also, in a switch statement $_ is the matched object. So putting this all together you get a basic grep (looking for the word "FileInfo" in all *.mshxml files) that looks like:
foreach ($f in resolve-path *.mshxml) { switch -file $f -regex { "FileInfo" { ($f.Path + ": " + $_ ) } } }
Finally, .Net has capture groups, like Perl, as discussed here; the groups wind up in the Monad variable $matches, so $matches[0] is the text matched by the whole regex, automatically numbered captures wind up in $matches[1], $matches[2], etc., and named captures (specified via (?<name>regex) in .Net) wind up in $matches["name"] ($matches is a hashtable, so $matches.name also works). Viz:
switch -file c:\boot.ini -regex { "(?<arcname>.*)=`"(?<displayname>.*)`"" { ("NAME " + $matches.displayname); ("ARC " + $matches.arcname) } }
The regular expression is:
"(?<arcname>.*)=`"(?<displayname>.*)`"
(Trust me, wade through it and you'll learn something.) That is put everything up to the first equal sign in a capture called arcname, then put everything between the double quotes in a capture called displayname (recall that the backtick ` is the Monad escape character, it escapes the double quotes here).
UPDATE: Lee Holmes had a blog entry about Monad regular expressions. In fact, it was an internal email about his entry, pointing out the switch -file syntax, that inspired this one.
Posted by AdamBa at July 26, 2005 11:30 AM
Trackback Pings
TrackBack URL for this entry:
http://proudlyserving.com/cgi-bin/mt-tb.cgi/272
