Try it with a very filled folder, though. I would expect the majority of the time spent is setup and actually going through the lines themselves isn't very slow.
On 22/07/2020 22:31, Aureliano Guedes wrote: > That is a little bit disappointing: > > $ time ls -l | perl -lane 'print "$F[7] $F[1]"' > /dev/null > > real 0m0.008s > user 0m0.013s > sys 0m0.000s > > $ time ls -l | raku -ne 'say "$_[7] $_[1]" given .words' > /dev/null > Use of Nil in string context > in block at -e line 1 > > real 0m0.302s > user 0m0.370s > sys 0m0.060s > > > The delay is so long that I wouldn't use that in a very filled folder. > Perhaps I know, it will be improved (I hope). > > On Wed, Jul 22, 2020 at 4:21 PM Larry Wall <la...@wall.org > <mailto:la...@wall.org>> wrote: > > On Sun, Jul 19, 2020 at 09:38:31PM -0700, William Michels via > perl6-users wrote: > : Hello, > : > : I ran across this 2010 Perl(5) article on the Oracle Linux Blog: > : > : "The top 10 tricks of Perl one-liners" > : > https://blogs.oracle.com/linux/the-top-10-tricks-of-perl-one-liners-v2 > : > : Q1. Now that it's a decade later--and Raku (née Perl6) has hit the > : scene--can someone translate the 'top ten tricks' in the blog > article > : above into Raku? > : > : Q2. Are many of the ten Perl(5) one-liner 'tricks' unnecessary > in Raku > : (better defaults, more regularized regexes, etc.)? > : > : Best, Bill. > > Yes, and yes. :-) > > More specificially, here's my take. > > > Trick #1: -l > > > > Smart newline processing. Normally, perl hands you entire > lines, > > including a trailing newline. With -l, it will strip the > trailing > > newline off of any lines read, and automatically add a > newline to > > anything you print (including via -p). > > > > Suppose I wanted to strip trailing whitespace from a > file. I might > > naïvely try something like > > > > perl -pe 's/\s*$//' > > > > The problem, however, is that the line ends with "\n", > which is > > whitespace, and so that snippet will also remove all > newlines from > > my file! -l solves the problem, by pulling off the > newline before > > handing my script the line, and then tacking a new one on > afterwards: > > > > perl -lpe 's/\s*$//' > > This trick is not needed in Raku, since newlines are stripped by > default. Also, > there are .trim methods that you can use instead of regex. > > > Trick #2: -0 > > > > Occasionally, it's useful to run a script over an entire > file, > > or over larger chunks at once. -0 makes -n and -p feed > you chunks > > split on NULL bytes instead of newlines. This is often > useful for, > > e.g. processing the output of find -print0. Furthermore, > perl -0777 > > makes perl not do any splitting, and pass entire files to > your script > > in $_. > > > > find . -name '*~' -print0 | perl -0ne unlink > > > > Could be used to delete all ~-files in a directory tree, > without > > having to remember how xargs works. > > The key word above is "occasionally", so most of these seldom-used > switches are gone. > Also, most of their functions are really easy to do from inside > the language. > So these days dividing a file by null chars would typicaly be > handled with: > > for slurp.split("\0") { ... } > > > Trick #3: -i > > > > -i tells perl to operate on files in-place. If you use -n > or -p with > > -i, and you pass perl filenames on the command-line, perl > will run > > your script on those files, and then replace their > contents with the > > output. -i optionally accepts an backup suffix as > argument; Perl will > > write backup copies of edited files to names with that > suffix added. > > > > perl -i.bak -ne 'print unless /^#/' script.sh > > > > Would strip all whole-line commands from script.sh, but > leave a copy > > of the original in script.sh.bak. > > I'm not aware of a direct replacement for this in Raku. Perl has > to be > better at something... > > > Trick #4: The .. operator > > > > Perl's .. operator is a stateful operator -- it remembers > state > > between evaluations. As long as its left operand is > false, it returns > > false; Once the left hand returns true, it starts > evaluating the > > right-hand operand until that becomes true, at which > point, on > > the next iteration it resets to false and starts testing > the other > > operand again. > > > > What does that mean in practice? It's a range operator: > It can be > > easily used to act on a range of lines in a file. For > instance, > > I can extract all GPG public keys from a file using: > > > > perl -ne 'print if /-----BEGIN PGP PUBLIC KEY > BLOCK-----/../-----END PGP PUBLIC KEY BLOCK-----/' FILE > > The scalar .. operator in Perl translates to the ff operator in Raku. > It's slightly less magical, however, insofar as it won't treat bare > numbers as line numbers in the input. > > > Trick #5: -a > > > > -a turns on autosplit mode – perl will automatically > split input > > lines on whitespace into the @F array. If you ever run > into any advice > > that accidentally escaped from 1980 telling you to use > awk because > > it automatically splits lines into fields, this is how > you use perl > > to do the same thing without learning another, even > worse, language. > > > > As an example, you could print a list of files along with > their link > > counts using > > > > ls -l | perl -lane 'print "$F[7] $F[1]"' > > This feature was always a bit suspect because it hard-wired a > particular > name. You don't even need a weird name in Raku: > > ls -l | raku -ne 'say "$_[7] $_[1]" given .words' > > > Trick #6: -F > > > > -F is used in conjunction with -a, to choose the delimiter on > > which to split lines. To print every user in /etc/passwd > (which is > > colon-separated with the user in the first column), we > could do: > > > > perl -F: -lane 'print $F[0]' /etc/passwd > > Again, we felt this switch wasn't really pulling it's weight, so > we pulled it > in favor of explicit split or comb: > > raku -ne 'say $_[0] given .split(":")' /etc/passwd > > > Trick #7: \K > > > > \K is undoubtedly my favorite little-known-feature of > Perl regular > > expressions. If \K appears in a regex, it causes the > regex matcher to > > drop everything before that point from the internal > record of "Which > > string did this regex match?". This is most useful in > conjunction > > with s///, where it gives you a simple way to match a > long expression, > > but only replace a suffix of it. > > > > Suppose I want to replace the From: field in an email. We > could > > write something like > > > > perl -lape 's/(^From:).*/$1 Nelson Elhage > <nelhage\@ksplice.com <http://ksplice.com>>/' > > > > But having to parenthesize the right bit and include the > $1 is > > annoying and error-prone. We can simplify the regex by > using \K to > > tell perl we won't want to replace the start of the match: > > > > perl -lape 's/^From:\K.*/ Nelson Elhage > <nelhage\@ksplice.com <http://ksplice.com>>/' > > Perl's \K \k becomes <( )> in Raku. Note that there are other > regex changes as well, > and that in the replacement it's not necessary to escape the @ in > the absence of brackets: > > raku -pe 's/ ^ "From:" <(.*)> / Nelson Elhage > <nelh...@ksplice.com <mailto:nelh...@ksplice.com>>/' > > The )> is not required to balance there, but helps clarify the > intention. If you do > have a quoting problem in the replacement, you can use the > assignment form with > any other form of quoting instead: > > raku -pe 's[ ^ "From:" <(.*)> ] = Q[Nelson Elhage > <nelh...@ksplice.com <mailto:nelh...@ksplice.com>>]' > > > Trick #8: $ENV{} > > > > When you're writing a one-liner using -e in the shell, > you generally > > want to quote it with ', so that dollar signs inside the > one-liner > > aren't expanded by the shell. But that makes it annoying > to use a ' > > inside your one-liner, since you can't escape a single > quote inside > > of single quotes, in the shell. > > > > Let's suppose we wanted to print the username of anyone > in /etc/passwd > > whose name included an apostrophe. One option would be to > use a > > standard shell-quoting trick to include the ': > > > perl -F: -lane 'print $F[0] if $F[4] =~ /'"'"'/' /etc/passwd > > > > But counting apostrophes and backslashes gets old fast. A > better > > option, in my opinion, is to use the environment to pass > the regex > > into perl, which lets you dodge a layer of parsing entirely: > > > > env re="'" perl -F: -lane 'print $F[0] if $F[4] =~ > /$ENV{re}/' /etc/passwd > > > > We use the env command to place the regex in a variable > called re, > > which we can then refer to from the perl script through > the %ENV > > hash. This way is slightly longer, but I find the savings > in counting > > backslashes or quotes to be worth it, especially if you > need to end > > up embedding strings with more than a single metacharacter. > > This is rather Unix-centric on the face of it, since on Windows you'd > have to use outer "" quoting instead. But you can certainly use the > same trick with Raku, provided you spell ENV right: > > env re="'" raku -ne '(say .[0] if .[4] ~~ /<{ %*ENV<re> }>/) > given .split(":")' /etc/passwd > > It probably won't be very efficient though, and doesn't do a thing > for readability. > Much easier to use a character name: > > raku -ne '(say .[0] if .[4] ~~ /\c[APOSTROPHE]/) given > .split(":")' /etc/passwd > > You could backport that trick to Perl using \N{} too, I guess. > > > Trick #9: BEGIN and END > > > > BEGIN { ... } and END { ... } let you put code that gets > run entirely > > before or after the loop over the lines. > > > > For example, I could sum the values in the second column > of a CSV > > file using: > > > > perl -F, -lane '$t += $F[1]; END { print $t }' > > Same trick, except you can omit the brackets: > > raku -ne 'my $t += [1] given .split(","); END say $t' > > Note the 'my' is required because strict is the default. > > > Trick #10: -MRegexp::Common > > > > Using -M on the command line tells perl to load the given > module > > before running your code. There are thousands of modules > available > > on CPAN, numerous of them potentially useful in > one-liners, but > > one of my favorite for one-liner use is Regexp::Common, > which, as > > its name suggests, contains regular expressions to match > numerous > > commonly-used pieces of data. > > > > The full set of regexes available in Regexp::Common is > available in > > its documentation, but here's an example of where I might > use it: > > > > Neither the ifconfig nor the ip tool that is supposed to > replace it > > provide, as far as I know, an easy way of extracting > information for > > use by scripts. The ifdata program provides such an > interface, but > > isn't installed everywhere. Using perl and > Regexp::Common, however, > > we can do a pretty decent job of extracing an IP from ips > output: > > > > ip address list eth0 | \ > > perl -MRegexp::Common -lne 'print $1 if /($RE{net}{IPv4})/' > > I don't know if there's anything quite comparable. And who's to say > what's "common" anymore... Certainly we have -M. But Raku's regex > and grammars are so much more powerful that these things are likely to > kept in more specific Grammar modules anyway, or just hand-rolled for > the purpose on the spot. > > > ~nelhage Join the discussion Comments ( 7 ) > > Larry > > > > -- > Aureliano Guedes > skype: aureliano.guedes > contato: (11) 94292-6110 > whatsapp +5511942926110
