Expanding variables in a string

Ruby
1

Hello,

If I have a string containing variables, how can I expand them?

I retrieve this string from a db so I cannot expand it at the time of
assignment.

Eg:

myaction = ‘perl #{ENV[‘HOME_SCRIPTS’]}/myscript.pl -#{params[:date]}’

I want to be able to do:

system(myaction)

but for this I have to expand the vars inside the script first.

Many Thanks,
Aman

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2

On Mon, Aug 11, 2008 at 6:00 AM, Thind, Aman [email protected]
wrote:

I want to be able to do:

system(myaction)

but for this I have to expand the vars inside the script first.

Many Thanks,
Aman

You mean you wish to execute in Ruby code you have in a string ?

If that’s wha you’re looking for then eval is what you want.

3

On Aug 11, 12:00 am, “Thind, Aman” [email protected] wrote:

I want to be able to do:

system(myaction)

but for this I have to expand the vars inside the script first.

Have you tried putting double quotes (rather than single quotes)
around the String in question?

v = “hello”
w = “1. #{v}” # → 1. hello
x = ‘2. #{v}’ # → 2. #{v}

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4

On Mon, Aug 11, 2008 at 6:39 AM, Thind, Aman [email protected]
wrote:

NameError: undefined local variable or method `perl’ for main:Object

Thanks,
Aman

Sorry, I misunderstood your problem.

You could try %Q, like this
h = {}
h[‘MY_THING’] = 78 # hash just for the example

myaction = %Q{perl with whaterver you want and also #{h[‘MY_THING’]}}
system myaction

Hope it helps.

5

2008/8/11 Thind, Aman [email protected]:

NameError: undefined local variable or method `perl’ for main:Object

You could try something like this:

myaction.gsub(/#{(.+?)}/){eval($1)}

Regards,

Park H.

6

Thanks for the reply!

If I do eval(myaction) then it thinks all the words in the string are
variables and complains:

irb(main):002:0> myaction = ‘perl #{ENV[HOME_SCRIPTS]}/myscript.pl
-#{params[:date]}’
=> “perl #{ENV[HOME_SCRIPTS]}/myscript.pl -#{params[:date]}”

irb(main):004:0> eval myaction
NameError: undefined local variable or method `perl’ for main:Object

What I want is for all the known variables in the string to be expanded;
the same effect that assignment with double quotes has.

Please remember I know using double quotes in the assignment to myaction
would solve the problem but I am doing this assignment only for
illustration.

I actually get the string from a db query so have to expand the
variables after the assignment.

Thanks,
Aman

7

On 11 Aug 2008, at 06:02, Heesob P. wrote:

irb(main):004:0> eval myaction

I actually get the string from a db query so have to expand the
variables after the assignment.

You could try something like this:

myaction.gsub(/#{(.+?)}/){eval($1)}

Or even
my_interpolated_action = eval “%@#{action.gsub(’@’,’@’)}@”
(lifted from activerecord where something similar is done)

Fred