How to expand shell variables in a text file?

Question

Consider a ASCII text file (lets say it contains code of a non-shell scripting language):

Text_File.msh:

spool on to \'$LOG_FILE_PATH/lo         


        

Answer 1

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

Answer 2

One limitation of the above answers is that they both require the variables to be exported to the environment. Here's what i came up with that would allow the variables to be local to the current shell script:

#!/bin/sh
FOO=bar;
FILE=`mktemp`; # Let the shell create a temporary file
trap 'rm -f $FILE' 0 1 2 3 15;   # Clean up the temporary file 

(
  echo 'cat <<END_OF_TEXT'
  cat "$@"
  echo 'END_OF_TEXT'
) > $FILE
. $FILE

The above example allows the variable $FOO to be substituted in the files named on the command line. I'm sure it can be improved, but this works for me so far.

Thanks to both previous answers for their ideas!

Answer 3

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

Answer 4

#logfiles.list:

$EAMSROOT/var/log/LinuxOSAgent.log
$EAMSROOT/var/log/PanacesServer.log
$EAMSROOT/var/log/PanacesStrutsGUI.log

#My Program:

cat logfiles.list | while read line
    do
        eval Eline=$line
        echo $Eline
    done

Answer 5

If a Perl solution is ok for you:

Sample file:

$ cat file.sh
spool on to '$HOME/logfile.log';
login 'username' 'password';

Solution:

$ perl -pe 's/\$(\w+)/$ENV{$1}/g' file.sh
spool on to '/home/user/logfile.log';
login 'username' 'password';

Answer 6

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".