Wednesday, June 16, 2010

Case insensitive regex in bash

By default regexes in [[ ]] are case sensitive. If you want to match in a case insensitive way you have to set the shell option nocasematch.

if [[ $mytext =~ existenz ]];
echo "yep"
echo "nope"

If you run the above script you should get "nope" as the output. For case insensitive matching just insert this into the script prior to the regex:

shopt -s nocasematch;

You can unset the nocasematch shell option using the following: shopt -u nocasematch

Here's a more complete example:

function testText
if [[ $mytext =~ existenz ]];
echo "yep"
echo "nope"
shopt -s nocasematch

If you run that script then the output is:


Sunday, June 13, 2010

R related links

These are just a few R links I think are interesting and worth a further read:

  1. Colour palettes in R.

  2. Using R for introductory statistics

  3. Web-friendly visualisations in R

  4. A different way to view probability densities

  5. Thoughts on Making Data Work

Also of note is Google's announcement (on June 2nd) that they were working with the USPTO to make all granted patents, trademarks and published applications freely available for download - see this post.

Tuesday, June 1, 2010

I love subshells

Sometimes it's the little things in life that give us the greatest pleasures. I love subshells. There, I admitted it.

Say you want to do something with the output of a program but would like to prepend some output/text that also needs to be operated on. The standard idiom would be to create a file with the prepended output, append your output to this and then operate on the file, but you can remove the intermediate files using a subshell. Here's a contrived example:

> (echo -e "some\toutput\tto\tappend"; perl -lane 'print join("\t", log($F[0])/log(10), @F[1 .. #$F])' ;) | a2ps

Something else I use subshells for a lot is to launch programs in a different directory without having to cd there and then back again:

> (cd ~/workspace/; eclipse &)

like I said; it's the little things.