Alex Muller

Shell scripting is really pretty good fun. I’m nowhere near claiming to be an expert (hell, I’ve been doing it for about three weeks now), but I kind of feel like I’m getting somewhere. Here’s some stuff I’ve been messing around with, hopefully accompanied by some clear explanations that, if nothing else, will help me get my head around it a little better. I’m playing with my chat logs because I’m obsessed with stats (hopefully you’ve figured that out by now).

Redirecting output

One of the most simple things, but it bears noting down. You can redirect the output of the bash shell by using the greater than symbol (>). Let’s build it up:

Will list all the files and folders in directory.

Applies the recursive -R switch, which will list all the files and folders, as well as any files inside any folders.

Now we get on to the redirecting output bit: the > part followed by a filename will take the output and put it in the file you named. Here’s the output – not that you care, or anything…

Grep

Grep is something different: a command for searching, basically. I’m going to use it with the file that was created above in order to make it more readable.

Will search for (and print) the lines containing “hello” in the file text file “example”. Clearly this is a pretty basic use of the tool, but it works. To get a bit more complicated:

Will print all the lines in the output_list file that contain the phrase “.chatlog”, and save them to the filtered_list file.

What’s changed? The egrep just tells grep to apply the -e flag, which will make it use regular expressions for searching. I haven’t bothered trying to understand these. For me, it’s only to add the $ sign to the end of the string to indicate it should only search for that at the end of a line. Here’s the output from the second part. Much easier to read, much easier to do stats on/with…

There you go

Hopefully that helps someone understand something a little better. If I’ve got something wrong, let me know please. I might report back if I can find it in me to manipulate the text file a little bit.

This is hardly complicated, but it’s something that’s been bugging me. A few minutes later, tada: a script that will open the Last.fm page of the currently playing iTunes track.

Copy and paste the above into Script Editor (Applications > AppleScript) on the Mac, and hit compile. As the comment in the code says, this is hardly my finest piece of work (at least, I hope it isn’t), so I’m not too bothered what you do with it. Enjoy it, whatever happens…