Sed failed to match non whitespace characters with character class

Question

I want to extract filter rules configured in /etc/lvm/lvm.conf, like filter = [ \"r|/dev/sda|\" ]. I want sed to return \"r|/dev

Answer 1

Alternatively easier and shorter than [^[:space:]] you can do with \S+ without using brackets []

\S means non whitespace char

echo ' filter = [ "r|/dev/sda|" ] ' | sed -r 's:^\s*filter\s*=\s*\[\s*(\S+)\s*\]:\1:g'

https://ideone.com/PxDX1Q

Answer 2

Acc. to regular-expressions.info:

One key syntactic difference is that the backslash is NOT a metacharacter in a POSIX bracket expression. So in POSIX, the regular expression [\d] matches a \ or a d.

So you need to replace [^\s] with [^[:space:]] (any char other than whitespace).

Example:

echo ' filter = [ "r|/dev/sda|" ] ' | sed -E 's:^\s*filter\s*=\s*\[\s*([^[:space:]]+)\s*\]:\1:g'

Output: "r|/dev/sda|"

Answer 3

In case grep solution is acceptable :

grep -oP 'filter.*\K".*?"' inputfile