sed plus sign doesn't work

Question

I'm trying to replace /./ or /././ or /./././ to / only in bash script. I've managed to create regex for sed but it doesn't work.

variable="something/./././"
variable=$(echo $variable | sed "s/\/(\.\/)+/\//g")
echo $variable # this should output "something/"

When I tried to replace only /./ substring it worked with regex in sed \/\.\/. Does sed regex requires more flags to use multiplication of substring with + or *?

Answer 1

Use -r option to make sed to use extended regular expression:

$ variable="something/./././"
$ echo $variable | sed -r "s/\/(\.\/)+/\//g"
something/

Answer 2

Any sed:

sed 's|/\(\./\)\{1,\}|/|g'

But a + or \{1,\} would not even be required in this case, a * would do nicely, so

sed 's|/\(\./\)*|/|g'

should suffice

Answer 3

Two things to make it simple:

$ variable="something/./././"
$ sed -r 's#(\./){1,}##' <<< "$variable"
something/

• Use {1,} to indicate one or more patterns. You won't need g with this.
• Use different delimiterers # in above case to make it readable
• + is ERE so you need to enable -E or -r option to use it

Answer 4

You can also do this with bash's built-in parameter substitution. This doesn't require sed, which doesn't accept -r on a Mac under OS X:

variable="something/./././"
a=${variable/\/*/}/                   # Remove slash and everything after it, then re-apply slash afterwards
echo $a
something/

See here for explanation and other examples.