Sed to Replace a string with variable

I have a data in variable which I need to replace a string in file with.

  app_name="Test 12 & - 3"
  echo "application_name" > test.txt
  sed  "s/application_name/$app_name/g" test.xt

I get following as output

Test 12 application_name - 3

instead of

Test 12 & - 3

The same command works fine if the var doesn’t have & but with & it doesnt work.

Any suggestions ?

Regards.

>Solution :

& in the substitution part of the s command has a special meaning in sed (and in other search and substitute facilities, such as Vim’s): it is substituted with the string that matched the search pattern, which in your case is the application_name string between the first two /s.

To include a literal &, you need to escape it when it appears in between the second and third /s of the sed command:

sed "s/application_name/${app_name/&/\\&}/g" test.txt

The ${app_name/&/\\&} part is nothing else than ${app_name} with & substituted by \& (since \ itself is a special character, I had to escape it too, \\&). See also man bash for more details (search for Pattern substitution in there).