How to expand shell variables in a text file?

This solution is not elegant, but it works. Create a script call shell_expansion.sh:

echo 'cat <<END_OF_TEXT' >  temp.sh
cat "$1"                 >> temp.sh
echo 'END_OF_TEXT'       >> temp.sh
bash temp.sh >> "$2"
rm temp.sh

You can then invoke this script as followed:

bash shell_expansion.sh Text_File.msh Text_File_expanded.msh

This question has been asked in another thread, and this is the best answer IMO:

export LOG_FILE_PATH=/expanded/path/of/the/log/file/../logfile.log
cat Text_File.msh | envsubst > Text_File_expanded.msh

if on Mac, install gettext first: brew install gettext

see: Forcing bash to expand variables in a string loaded from a file

If you want it in one line (I'm not a bash expert so there may be caveats to this but it works everywhere I've tried it):

when test.txt contains

${line1}
${line2}

then:

>line1=fark
>line2=fork
>value=$(eval "echo \"$(cat test.txt)\"")
>echo "$value"
line1 says fark
line2 says fork

Obviously if you just want to print it you can take out the extra value=$() and echo "$value".

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