linux + bash + export parameters in to a new file from data file

Question

I have Linux machine red-hat 5.1 and I ask the following question

my target is to create new output_file.txt file from answer_file.txt according to data_file.txt

as we see here I run first the data_file.txt and export all parameters from the file then I try to print all answer_file.txt in to new file output_file.txt

so I will get this file with the new parameters from data_file.txt but I not success -:(

please advice how to export the parameters from data_file.txt in to answer_file.txt and then create new file with the correct values?

remark - I work with bash and I not want to use sed or awk for this task , and I not want to change the content of the original data_file.txt or answer_file.txt ( I need the simple way from bash shell to do the Job )

 [root@test1a /var/tmp]# more data_file.txt 
 arg1=a
 arg2=b
 arg3=c


 [root@test1a /var/tmp]# more answer_file.txt
 param1=$arg1
 param2=$arg2
 param3=$arg3



 [root@test1a /var/tmp]#  . ./data_file.txt 
 [root@test1a /var/tmp]# export arg1 arg2 arg3
 [root@test1a /var/tmp]#  cat `  . ./answer_file.txt  `  >/var/tmp/output_file.txt
 -bash: ./answer_file.txt: line 4: unexpected EOF while looking for matching `''
 -bash: ./answer_file.txt: line 5: syntax error: unexpected end of file






 ( my target is to get: Example of expected results from output_file.txt )

    more answer_file.txt  
    param1=a  
    param2=b  
    param3=c

Answer 1

You need to run eval on each line in the file. Try this:

$ cat data_file.txt
arg1=a
arg2=b
arg3=c

$ cat answer_file.txt
param1=$arg1
param2=$arg2
param3=$arg3

$ . data_file.txt

$ eval "echo \"$(cat answer_file.txt)\""
param1=a
param2=b
param3=c

# alternative, shorter command
$ eval "echo \"$(<answer_file.txt)\""
param1=a
param2=b
param3=c

Answer 2

Sorry I didn't flesh this out more fully, I'm a bit tired (community, feel free to edit this and step in). Hopefully this will get you started with what you need:

$ cat data.txt
arg1=a
arg2=b
arg3=c
export arg1 arg2 arg3
$ cat answer.txt
echo param1=$arg1
param2=$arg2
param3=$arg3
$ eval `cat data.txt`;eval `cat answer.txt`
param1=a param2=b param3=c