Interpolating strings within strings

Darby has asked for the wisdom of the Perl Monks concerning the following question:

I am working on a library module to replace an aging shell script. It (among a few other things) reads in a variety of FTP commands from a file and then performs the given FTP transaction. The system in question doesn't have Net::FTP, so that won't work much as I would prefer using that. My module will read in the config files, set up a hash with all the relevant information and return it upon request. The problem I am having is that the FTP commands in the file include variables which are set in the module. In my calling program, I call various methods in the module, print the relevant FTP transaction to a file and then call FTP passing in that file. Easy enough usually. I have a few lines of code like so:

      while (my $command = $ftpgizmo->next_ftp_command )
      {
         print OUT "${command}\n";
      }
[download]

Now $command is going to be a string like:

cd $FTPPath
or
type ${TransferMode}
[download]

This is exactly what prints out though. How would I go about making sure that these variables are interpolated so that it prints out

cd /my/ftp/path
or
type ASCII
[download]

Currently, in the next_ftp_command, I define and set these variables before returning the given string, but this doesn't work.
Thanks,
Doug

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Re: Interpolating strings within strings by ccn (Vicar) on Sep 29, 2004 at 16:21 UTC
`while (my $command = $ftpgizmo->next_ftp_command ) { print OUT eval qq{"$command\n"}; }` [download]	[reply] [d/l]
Re^2: Interpolating strings within strings by Darby (Sexton) on Sep 29, 2004 at 16:47 UTC
Awesome, you guys are great. Thanks a lot. Doug	[reply]
Re^3: Interpolating strings within strings by ikegami (Patriarch) on Sep 29, 2004 at 17:44 UTC
If your variables are in a hash, the following doesn't compile the string at runtime. It's safer and possibly faster. I've even added an esacpe sequence (`${$}`) in case you need to use `$`! `%vars = ( FTPPath => '/my/ftp/path', TransferMode => 'ASCII', ); s/(\$(\w+\|{(\$\|\w+)}))/ my $var = defined($3) ? $3 : $2; $var eq '$' ? '$' : (defined($vars{$var}) ? $vars{$var} : $1); /eg;` [download] Test code: Read more... (722 Bytes)	[reply] [d/l] [select]
Re: Interpolating strings within strings by diotalevi (Canon) on Sep 29, 2004 at 16:18 UTC
Use sprintf. `return sprintf "cd %s", $FTPPath;`	[reply] [d/l]
Re: Interpolating strings within strings by amphiplex (Monk) on Sep 29, 2004 at 16:33 UTC
`eval` should do it, but you have to make sure that the command string gets double-quotes left and right. an example: `my $FTPPath = "/my/ftp/path"; my $command = 'cd $FTPPath'; my $command_new = eval "\"$command\""; print "$command_new\n";` [download] ---- amphiplex	[reply] [d/l]