Devoxx UA

Most conferences have been cancelled, since it is difficult to hold a conference these days. The idea to move the conference online has been obviously around, but it was rejected by most organizers, because it it not the same and the all important chance to meet other people is just not the same.  So the Devoxx in Antwerp, which I like to visit every year, did not happen.  But Devoxx Ukraine decided to go for online.

So how did it work:  There were three tracks.  Each track was represented by a youtube channel, on which the live talk was transmitted.  Before and after the talks, professional moderators appeared in these channels, announced the speakers and did what moderators do in normal conferences.  The devoxx App worked on my cell phone and that seemed to be the most up to date schedule.

Some talks were really excellent.  I enjoyed them a lot even online.  For talks that are not so good, it requires more discipline to stay tuned.

The discussion was done in zoom channels that belonged to the three tracks.  So discussions could technically last until the end of the next talk.  The discussions in zoom also worked quite well, which was a surprise.

I think it is probably the right reaction, to have fewer conferences than usually in a year and to cancel some and move some to online, exactly as it is happening.  I think DevoxxUA had around 10’000 visitors, so they absorbed audiences of several conferences.  Also some common speakers at Devoxx conferences were not giving talks, so I assume that also part of the speakers decided that the online format is not ideal for them.

About the contents I will write in another Blog article.

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How to rename files according to a pattern

We often encounter situations, where a large number of files should be copied or renamed or moved or something like that.
This can be done on the Linux command line, but it should be possible in almost the same way on the Unix/Linux/Cygwin-command line of newer MS-Windows or MacOS-X.

Now people routinely do that and they have developed several ways of doing it, which are all valid and useful.

I will show how I do things like that. It works and it is not the only way to do it.

So in the most simple case, all files in a directory ending in ‚.a‘ should be renamed to ‚.b‘.

What I do is:


ls *.a \
|perl -p -e 'chomp;$x = $_;s/\.a$/.b/;$y = $_; s/.+/mv $x $y\n/;' \
|egrep '^mv '\
|sh

You can run it without the last |sh, to check if it really does what you want.

So I use the files as input to a short perl script and create shell commands. It would be possible to do this actually in Perl itself, without piping it into a shell:


ls *.b \
|perl -n -e 'chomp;$x = $_;s/\.b$/.c/;$y=$_;rename $x, $y;'

You could also read the directory from perl, it is quite easy, but for just quickly doing stuff, I prefer getting the input from some ls.

To go into sub directories, you can use find:


find . -name '*.c' -type f -print \
| perl -n -e 'chomp;$x = $_;s/\.c$/.d/;$y=$_;rename $x, $y;'

a
You can also rename all the files that contain a certain string:

find . -name '*.html' -type f -print \
|xargs egrep -l form \
|perl -n -e 'chomp; $x=$_;s/\.html$/.form/;$y=$_;rename $x, $y;'

So you can combine with all kinds of shell commands and do really a lot of things in one line.

Of course you can use Raku, Ruby, Python or your favorite scripting language instead, as long as it allows some simple pattern matching and an efficient implicit iteration over the lines.

For such simple tasks there are also ways to do it directly in the shell like this

for f in *.d ; do mv $f `basename $f .d`.e; done

And you can always use sed, possibly in conjunction with awk instead of perl for such simple tasks.

Another approach is to just pipe the files into an texteditor that is powerful enough and create a one time script using powerful editing commands.
On Linux and Unix servers we almost always use vi, even people like me, who prefer Emacs on their own computer:

ls *.e > tmpscript
vi tmpscript

and then in vi


:0,$s/\(.*\)\(.e\)$/mv \1\2 \1.f/
ZZ

and then

sh tmpscript
rm tmpscript

So, there are many ways to achieve this goal and they are flexible and powerful enough to do really a lot more than just such simple pattern renaming.

If you work in a team and put these things into scripts, it might be necessary to follow a team policy about which scripting languages are preferred and which patterns are preferred. And you need to know the stuff that you write yourself, but also the stuff that your colleagues write.

Please, do not do

mv *.a *.b

It won’t work for good reasons.
On Linux and Unix systems the shell (usually bash) expands the glob expression (the stuff with the stars) into a list of strings and then starts mv with these strings a parameters. So calling mv with some file names ending in .a and .b, mv cannot have any idea what to do. When called with more than two parameters, the last one needs to be a directory where to move the stuff, so usually it will just refuse to work.

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