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sudo !!

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A time-saver for those that forget to sudo, bash substitutes !! for the last command entered, for example

charles@lucifer$ make sandwich

Permission Denied!

charles@lucifer$ sudo !!

sudo make sandwich

echo "You seriously think I would write a sandwich recipe just to demonstrate bash shortcut?"

You seriously think I would write a sandwich recipe just to demonstrate a bash shortcut?

Walking a directory tree with bash

Posted in

I'm doing the hard-drive shuffle thing. I have a lot of data and I'm paranoid about losing it. I've been let down once or twice by bad copies so I thought I should take checksums before copying. I had a lot of fun arguing with wildcards and string escaping so I thought I'd share my adventure, as I've already worked out how to do this and forgotten at least once.

My first attempt. It dies when fed directories.

md5sum * | md5sums.txt

I try again, and it occours to me to use tee in append mode so I get output to the screen as well

for foo in `ls -R` do
md5sum $foo | tee -a md5sums.txt
done

This doesn't work, md5sum complains. I have a look at  ls -R

Quote:
some.file
another.file

Directory1/
Directory2/

Directory1:
inDirectory1.file
inDirectory1again.file

Directory2:
inDirectory2.file
inDirectory2again.file

I RTFM and can't find an option to list full paths. I consider using find.

for foo in `find -type f` do
md5sum $foo | tee -a md5sums.txt
done

This fails when anything has a space in the filename. I RTFM on find. find -ls does the escaping i need but has all the useful info that ls -l spits out. Not too handy and I don't feel like resorting to sed, or awk. Further through the fine manual I find

man find wrote:
-exec command ;
Execute command; true if 0 status is returned. All following arguments to find are taken to be
arguments to the command until an argument consisting of ‘;’ is encountered. The string ‘{}’ is
replaced by the current file name being processed everywhere it occurs in the arguments to the
command

To cut a long story short that's not quite the whole truth, as the shell works its magic on {} and ; so we need to add quotes and a slash.

find -type f -exec md5sum '{}' \; | tee md5sums.txt  

Of course as I watch the damn thing run I start wondering about how to perform the md5sums in parallel to get it done faster. I start the same command on the copy of the files and notice that find lists the files in a different order, so I'm going to need to apply sort and whilst I'm at it I should probably use the list to strip out any of the inevitable duplicate files I have kicking around.

Or I could have just installed md5deep.

Do the same thing to many files when wildcards break

Posted in

This is a gem I use a lot, and forget a lot, so it's write it down time.

Suppose I have a folder with a number of tarballs in it and I want to extract all of them, tar -xf *.tar won't work as tar will try and extract all but the first file that matches the wild card from the first item. We break out the trusty for loop.

for foo in `ls *.tar`
do
tar -xf $foo
done

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