diff – even before you have had your morning coffee
| April 22nd, 2008diff is a fabulous tool. Most of the time it is used to compare files. in this case we are going to use it to compare the output of two commands.
For a simple example, I have two directories of images, the file names are the same. The directory ./big has larger versions of the images, where as ./medium has medium sized versions for use on the web. Some of the images may be missing from the directories. Maybe the person converting them added a letter ‘s’ to the end of a file name inadvertently? But which ones?
well we could use ls. I’ll show my entire command line here:
jonny@taft:~/Desktop/images$ ls ./*this is the output
./big:
air.jpg barrels.jpg garbage.jpg photo.jpg smoke.jpg
autos.jpg beam.jpg jordan.jpg plane.jpg turm.jpg
balloon.jpg crack.jpg mouth.jpg rubble.jpg utopia.jpg
./medium:
air.jpg beams.jpg detailTwo.jpg jordan.jpg rubble.jpg
autos.jpg canada.jpg garbage.jpg mouth.jpg smoke.jpg
balloon.jpg crack.jpg hillary.jpg photo.jpg turm.jpg
barrels.jpg detailOne.jpg identity.jpg plane.jpg utopia.jpg
I could compare the list of files visually, but I say “let robots’ brains do robots’ work”
This would be the cool way (which is the way the cool kids are doing things) to do the same job:
diff <(ls ./big) <(ls ./medium)and here is what that looks like:
5c5,6
< beam.jpg
---
> beams.jpg
> canada.jpg
6a8,9
> detailOne.jpg
> detailTwo.jpg
7a11,12
> hillary.jpg
> identity.jpgI think too many times, I miss items, or see things that aren't there when I'm comparing lists visually. Robots are harder to trick at jobs like comparing lists or counting.
... a dba thought I should be able to compare long lists of numbers visually. Since I was a programmer after all, I should have that ability right?? Personally I don't think the task of comparing long strings of numbers visually should be required of a programmer analyst/dba. I like results that I can test with a machine. Robots' brains are for robots' work, people brains are for thinking creatively within a framework of good methods, to solve interesting problems.
as usual ... here is a page with some useful tips including a version of the one above.
http://www.linuxtutorialblog.com