jvisualvm instead of kill -3

Whenever I need to see what's going on under the hood of a process I issue a kill -3 to get a stack-trace. Well, I was just introduced to jvisualvm! This is a great way to see what's going on with a running java process.

Changing the mysql prompt

This is such an obvious thing to do, why didn't I do it before?

I'm constantly jumping into and between multiple databases as multiple users (test, standard, mysql) it becomes a little dangerous and I'm finding myself checking where I am and who I am:
SELECT user();
SELECT database();

but you can change the standard mysql prompt to display the user and database! Just edit the my.cnf file and place the following under [mysql]:

prompt=\\u@\\d:

Now my prompt looks like this:
paul@test:
or
root@main:

If you don't have permissions to alter the my.cnf directly, then you could change your personal .bashrc (or equivalent) to contain something like this:

alias mysql='mysql --prompt="\u@\d:"'

This has saved me a lot of paranoia (and probably some headaches).

bash substring substitution

I just came across this today, it's something that I wish I'd known years ago (I think it just shows that I need to read more manuals), I've been emulating this feature with Perl and regexes or with the basename/dirname commands.

It's very simple; today I wanted to run through a set of files with a particular file extension, do some processing and then print the output to another file named the same as the original but with a different extension.

So, say the files are .tsv (tab delimited) and I want to create a .csv (comma delimited) one from the first two columns, you can do it like this:

for file in `ls *.tsv`;
  do cut -f1,2 --output-delimiter=, \
  $file > ${file/.tsv/.csv};
done

Sweet, eh?