From: Kaspar Schiess <eule@...>
Date: 2004-10-14T20:50:00+09:00
Subject: Re: [nuby] shell-like substitution in a string

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Hello Lionel,

That was quite a quiz you asked us ;)

I have a solution using only 'regular' regular expressions, the one in
1.8.1. Thus: this solution works without oniguruma.

I work around the lookbehind trouble by appending three spaces in front
of the string.

I am sure this solution is hideously complicated and can be improoved.
Anyone ?

Here's the output:
~ bluna ${var\}weird}
~ bluna weird substitute

~ sh ${tool} -o ${target} -L${libpath} -l${lib} ${source}
~ sh gcc -o test.exe -L/usr/lib -lopengl render.c

~ \${var}
~ \${var}

~ \\${var}
~ \\rvar

~ $\${var}
~ $\${var}

~ $\$${var}
~ $\$rvar

with an env of

~ env = {
	'var\}weird' => 'weird substitute',
	'var' => 'rvar',
	'tool' => 'gcc',
	'target' => 'test.exe',
	'libpath' => '/usr/lib',
	'lib' => 'opengl',
	'source' => 'render.c'
~ }

Hope this hits your nerv,
kaspar
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tests = []

tests << 'bluna ${var\\}weird}'
tests << 'sh ${tool} -o ${target} -L${libpath} -l${lib} ${source}'
tests << '\\${var}'
tests << '\\\\${var}'
tests << '$\${var}'
tests << '$\$${var}'


env = {
	'var\}weird' => 'weird substitute',
	'var' => 'rvar', 
	'tool' => 'gcc', 
	'target' => 'test.exe', 
	'libpath' => '/usr/lib', 
	'lib' => 'opengl', 
	'source' => 'render.c'
}

class ShellExpander
	REString = /
		^ 
		(?:
			\\ . |
			[^\\$] |
			\$ \\ . |
			\$ [^\\{]
		){3,}
		\$ \{
		(
			(?: \\ . | [^\\}] )*
		)
		}
	/x

	def initialize env={}
		@env = env
	end
	
	# call-seq: 
	#  #expand( str ) => str
	def expand str
		for_each_shell_expansion_in str do |var|
			@env[var]
		end
	end
	
	def for_each_shell_expansion_in str
		tomatch = str
		replacements = []
		offset = 0
		while str.length > 0 
			tomatch = ' '*3 + tomatch
			offset -= 3
			md = REString.match tomatch
			break unless md
			
			replacement = yield( md[1] )
			i, j = offset+md.begin(1), offset+md.end(1)
			
			replacements << [i, j, replacement] if replacement
			
			offset += md.pre_match.length + md[0].length
			tomatch = md.post_match
		end

		offset = 0
		replacements.each do |from, to, rep|
			str[ (offset+from-2)...(offset+to+1) ] = rep
			
			offset += rep.length - (to-from+3)
		end
		
		str
	end
end

expander = ShellExpander.new env

tests.each do |str|
	puts
	puts str
	puts expander.expand(str)
end



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