grep -ilR 'foo' * | xargs grep -il 'bar' | etc...

• grep -R --include='*.txt' 'search string' *

• find -type f -name '*.txt' -print0 | \
  xargs -0 grep 'search string'

While grep’s include directive is certainly more concise, I’d argue that learning all of the general case is more useful in the long run. What if you want to exclude a certain path? What it you want to change file permissions instead of grepping? Combining find with xargs tends to be far more flexible than the alternatives.

Examples

• find -type f -not \( -path '*/.svn/*' -a -prune \) \
  -print0 | xargs -0 grep 'search string'

• find -type f -print0 | xargs -0 du | sort -g | tail

# First remove any pre-existing links
find . -type l -print0 | xargs -0 rm;
# Then symbolically link dir2 into dir1
for file in `cd dir2; find`; do
	if [ ! -e dir1/$file ]; then
		depth=`echo $file | awk -F '/' '{print NF}'`;
		prefix=`perl -e 'print "../"x$ARGV[0]' $depth`;
		ln -s "$prefix"dir2/$file dir1/$file;
	fi
done

Well, I can download a fresh copy of the code base and compare, right? Here’s how you can do that.

find ./path -type f -print0 | xargs -0 md5sum > path.md5s;

Do the same to the fresh installation and diff the outputs. That should give you a reasonable feel for what’s changed, yeah? I don’t know if this is the best approach, so if you know a better way, please tell me.

Update: Seems that diff -urN path1 path2 will do it one better and show the contents of what changed. It doesn’t have the same power of pruning subdirectories that you’d expect from find, but in most cases it’s strictly better.

I’m honestly surprised that site only came about within the last six months. Applying social aggregation to tips within a field seems obvious now. That’s the thing with good ideas, yeah?

mysqldump --where="true LIMIT X" schema > output.sql

Unfortunately, this doesn’t allow for any granularity in the number of rows returned. Still, “get me the database and at most 1000 rows from each table” can be helpful in certain situations.

• iotop
• iftop
• mytop
• apachetop

watch --differences -n 5 'df; ls -FlAt;'

It basically says “keep printing out disk usage and recently modified files every 5 seconds until I say otherwise”. Run that inside of /var/lib/mysql/foo and you’re set.

for i in `seq 1 10` do ssh instance$i rcapache2 restart; done

It basically says “connect to instance1, instance2 and so on and restart the apache server on each”. This approach could easily be modified for more complex tasks. That it’s done on one line is what catches my attention. Prior to seeing this done, I would have SSHed into each server by hand.

du -k --max-depth=X | sort -r -g | head -n Y

It basically says “from the current directory, list everything at most X deep by kilobytes, sort it in descending order and only show me the top Y results”. With values like X=4 and Y=10, you’re bound to find the behemoths.

Update

Here’s another way of getting the same results, but with the option for further refinement.

find -size +1M -type f -print0 | xargs -0 ls -Ssh1 | head
find -size +1M -exec du -sk {} \; | sort -nr | less