Question

Let’s say I have a template text file most of whose content is static but has some variables. E.g.

My favorite site is ${FAV_SITE}

Let’s say that FAV_SITE is set to stackoverflow.com:

export FAV_SITE=stackoverflow.com

How do I print to STDOUT the contents of the file with the vars resolved, i.e.

My favorite site is stackoverflow.com

without using fancy tools like sed or awk?

Answer 1

Using Perl:

#!/usr/bin/perl

use strict;

my $inFile = $ARGV[0];

print "\nInput File=".$inFile;

open(FILEHANDLE, "<$inFile") || die("Could not open file");

my @fileLines = <FILEHANDLE>;

my $rslt;

foreach my $line(@fileLines)
{
    #chomp($line);

    #print "\nLINE BEFORE=".$line;

    while($line =~ m/(\${\w+})/g)
    {
        if($1)
        {
            my $plchldr = $1;

            my $varName = $plchldr;

            $varName =~ s/(\$|{|})//g;

            my $varVal = $ENV{$varName};

            if($varVal)
            {
                $line =~ s/\Q$plchldr/$varVal/g;
            }
        }
    }

    $rslt .= $line;

    #print "\nLINE AFTER=".$line;
}

print "\nRESULT = ".$rslt;

close(FILEHANDLE);

print "\n";

exit(0);