Removing substring out of string using sed

Question

I am trying to remove substring out of variable using sed like this:

PRINT_THIS="`echo "$fullpath" | sed 's/${rootpath}//' -`"

where

fullpath="/media/some path/dir/helloworld/src"
rootpath=/media/some path/dir

I want to echo just rest of the fullpath like this (i am using this on whole bunch of directories, so I need to store it in variables and do it automatically

echo "helloworld/src"

using variable it would be

echo "Directory: $PRINT_THIS"

Problem is, I can not get sed to remove the substring, what I am I doing wrong? Thanks

Answer 1

You don't need sed for that, bash alone is enough:

$ fullpath="/media/some path/dir/helloworld/src"
$ rootpath="/media/some path/dir"
$ echo ${fullpath#${rootpath}}
/helloworld/src
$ echo ${fullpath#${rootpath}/}
helloworld/src
$ rootpath=unrelated
$ echo ${fullpath#${rootpath}/}
/media/some path/dir/helloworld/src

Check out the String manipulation documentation.

Answer 2

To use variables in sed, you must use it like this :

sed "s@$variable@@g" FILE

two things :

• I use double quotes (shell don't expand variables in single quotes)
• I use another separator that doesn't conflict with the slashes in your paths

Ex:

$ rootpath="/media/some path/dir"
$ fullpath="/media/some path/dir/helloworld/src"
$ echo "$fullpath"
/media/some path/dir/helloworld/src
$ echo "$fullpath" | sed "s@$rootpath@@"
/helloworld/src