2011-03-18-improving-irb-history.markdown

title	description	keywords	category	layout
Improving IRB history	Improving IRB history. Some ways to improve your interaction with IRB history	ruby, irb, console	ruby	articles

I’ve started to consider irb configurations as a way to improve my productivity. Following this path I’ve got some nice stuff in my irbrc. In the last days I was thinking about how to make irb history more similar to the bash one. So, I thought there was a need for the following features:

• History command
• History execute
• History grep

Also, ignoring duplicated lines on irb exit would be great.

##. The methods

That’s why the best thing I can do now is to show you the code I wrote to achieve the above mentioned features:

{% highlight ruby %} def history_a(n=Readline::HISTORY.size) size=Readline::HISTORY.size Readline::HISTORY.to_a[(size - n)..size-1] end

def decorate_h(n) size=Readline::HISTORY.size ((size - n)..size-1).zip(history_a(n)).map {|e| e.join(" ")} end

def h(n=10) entries = decorate_h(n) puts entries entries.size end

def hgrep(word) matched=decorate_h(Readline::HISTORY.size - 1).select {|h| h.match(word)} puts matched matched.size end

def h!(start, stop=nil) stop=start unless stop code = history_a[start..stop] code.each_with_index { |e,i| irb_context.evaluate(e,i) } Readline::HISTORY.pop code.each { |l| Readline::HISTORY.push l } puts code end {% endhighlight %}

Let me confess I don’t like a lot the naming of some methods :) By the way, these methods make the following output possibile:

{% highlight ruby %} ruby-1.9.2-p0 > h 199 h 200 h 201 hgrep "json" 202 h 203 h 204 h "toy" 205 h 206 hgrep "toy" 207 h! 197 208 h => 10 ruby-1.9.2-p0 > hgrep "toy" 89 a=Arra.toy 97 a=Array.toy 189 a=Arra.toy 197 a=Array.toy 204 h "toy" 206 hgrep "toy" 209 hgrep "toy" => 7 ruby-1.9.2-p0 > h! 197 a=Array.toy => nil ruby-1.9.2-p0 > a=Array.toy => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] {% endhighlight %}

I do know there are many posts around the web on this subject but I do not like some aspects of the solutions I came across. I wanted a bash like history and none of the solutions I found has a real working re-execute command. I found some solutions but all of them use eval to execute code and don’t replace the re-executed command in the history. Actually the h! method I wrote uses irb_context to evaluate the input lines. The issue with the eval version is easy to explain with an example:

{% highlight ruby %} ruby-1.9.2-p0 > eval("a=Array.toy") => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] ruby-1.9.2-p0 > a NameError: undefined local variable or method a' for main:Object from (irb):2 from /home/lucapette/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in

' ruby-1.9.2-p0 > a=Array.toy => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] ruby-1.9.2-p0 > a="l" => "l" ruby-1.9.2-p0 > h 5 200 eval("a=Array.toy") 201 a 202 a=Array.toy 203 a="l" 204 h 5 => 5 ruby-1.9.2-p0 > h! 202 a=Array.toy => nil ruby-1.9.2-p0 > a => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] {% endhighlight %}

Not a very big deal but I really prefer my implementation of the re-execute command. However, I can’t really explain the difference between the two implementations. I think it could be a scope problem, please tell me if I’m wrong.

Erasing duplicates

The last feature I wanted to have in my irb history is an equivalent to bash:

{% highlight bash %} export HISTCONTROL=erasedups {% endhighlight %}

this of course means erasing your duplicates command lines. So I came up with the following:

{% highlight ruby %}

don't save duplicates

IRB.conf[:AT_EXIT].unshift Proc.new { no_dups = [] Readline::HISTORY.each_with_index { |e,i| begin no_dups << e if Readline::HISTORY[i] != Readline::HISTORY[i+1] rescue IndexError end } Readline::HISTORY.clear no_dups.each { |e| Readline::HISTORY.push e } } {% endhighlight %}

I confess I do not like a lot the final implementation of the algorithm I wrote. But it does his job: IRB.conf[:AT_EXIT] is an array of proc that irb would call when you leave it. Thus, I simply added a proc that willy rewrite your irb history with uniq lines. Please tell me if you can do the same using a more elegant solution.

yaih

Well, the history commands we talked about could be a nice improvement in your irbrc too. I published a gem to share these methods with you. Install it with:

{% highlight ruby %} gem install yaih {% endhighlight %}

and then require it in your irbrc. I published yaih just a couple of days ago and it has some lacks. I would like to write some tests for it but I need some suggestion because I don’t know how I can write effective tests in this kind of situation. Then I’d like to add some options, especially if someone will kindly suggest me some :)