Integer conversions in bash

Since version 2, bash support a single aritmethic operations. Altough bash is not a mathematical shell (use bc instead), you can perform certain conversions using the bash arithmetic logic.

For example you can remove the left zeroes in a decimal number without require any external utility or print formats, let’s suppose that you want to strip zeroes from the number 007, which is stored in bond variable.

$ echo $bond
007
$ let nozeros=10#$bond
$ echo $nozeros
7

In many forums and mailing list, people need to use ugly sed expressions, or awk invokation, but (with bash) it’s just simply

Using the same trick, you can perform a base conversions, for example:

$ let i=0x10
$ echo $i
16
$ let i=2#10000
$ echo $i
16

Or create an easy number checking:

$ is_decimal () { let i=10#$1 2>/dev/null; }
$ is_decimal 'a' || echo Nop
Nop
$ is_decimal 56 && echo 'Yep'
Yep

Enjoy!

Update dot files with git

For a years I was using a custom created scripts to keep my dot files updated. I had a local repository in bazaar and a script which check differences between home dot files and files stored in the repository. This solutions works fine for years, but now I want to do some changes…

The first one is moving my dot files to git (and probably pushed them to github), and the second one is to create a hook for git to update my dot files. I known that there are a lot of similar solutions, one more complex, other more easy, but this is mine

So, I created a post-commit hook script for git, which perform the modifications that I need. Now I just only do this steps:

1. Create a new git repo:

mkdir mydots_repo
cd my_dots_repo && git init

2. Put the hook:

wget -O .git/hooks/post-commit  http://2tu.us/2scm 
chmod 755 .git/hooks/post-commit

3. Copy old files:

cp ~/old/bzr_repo/* .
git add *
 

4. Commit and recreate links:

git commit -a -m'initial import'

And it’s works