Sed replace value with variable

Question

I have a variable in a config, which I would like to replace with a value.

ROOT="rROOT"

I would like to replace that with

ROOT="$root"

So with the value of $root (Important are the quotation marks).

So far I have tried it that way

sed -i s/'ROOT=rROOT'/'ROOT="$root"'/g $directory/settings.conf

The result is that

ROOT="$root"

But this is stored in the variable $root (It is always a path)

root: /

How can I replace rROOT with the value of $root?

Sed Version: (GNU sed) 4.2.2

See: [Difference between single and double quotes in bash](http://stackoverflow.com/q/6697753/3776858) — Cyrus, Feb 17 '18 at 09:38

score 5 · Answer 1 · answered Feb 17 '18 at 13:20

Ok, don't like to ruin my scripts for testing:

cat tageslog.sh | sed "s/alt=185094/alt=\${root}/g"

Use double quotes, but mask the dollar sign, so it doesn't get lost and root interpreted while calling sed.

Use ${root} instead of "$root".

sed "s/ROOT=.rRoot./ROOT=\${root}/g" $directory/settings.conf

if this works, use the -i switch:

sed -i "s/ROOT=.rRoot./ROOT=\${root}/g" $directory/settings.conf

score 0 · Answer 2 · answered Feb 17 '18 at 13:15

You have different problems:

Testing with echo
I think you tested your command with
echo ROOT="rROOT" | sed s/'ROOT=rROOT'/'ROOT="$root"'/g
The double quotes won't appear in the output of the echo, so you will end up with a command working for ROOT=rROOT.
When the inputfile has qouble quotes, you do not have to insert them.
Testing with the double quotes is possible with
echo 'ROOT="rROOT"' | sed s/'ROOT=rROOT'/'ROOT="$root"'/g
Place the double quotes outside the single quotes; You can test this with echo:
echo 'Showing "$PWD" in double quotes is "'$PWD'"'
echo 'With additional spaces the last part is " '$PWD' " '
Root vaiable has slashes that will confuse sed.
The root variable is replaced before sed tries to understand the command.
You can use another character, like #, in the sed command: sed 's#before#after#'

When your input has double quotes:

echo 'ROOT="rROOT"' | sed 's#ROOT="rROOT"#ROOT="'$root'"#g'
# or by remembering strings
echo 'ROOT="rROOT"' | sed -r 's#(ROOT=")rROOT(")#\1'$root'\2#g'

Input without double quotes

echo 'ROOT=rROOT' | sed 's#ROOT=rROOT#ROOT="'$root'"#g'
# or by remembering strings
echo 'ROOT=rROOT' | sed -r 's#(ROOT=)rROOT#\1"'$root'"#g'

Sed replace value with variable

2 Answers2