正则表达式匹配但 sed 无法替换

Question

I am having a tricky regex issue

I have the string like below

some_Name   _  _Bday Date Comm.txt

And here is my regex to match the spaces and underscore

\_?\s\_?

Now when i try to replace the string using sed and the above regex

echo "some_Name   _  _Bday Date Comm.txt" | sed 's/\_?\s\_?/\_/g'

The output i want is

some_Name_Bday_Date_Comm.txt

Any ideas on how do i go about this ?

Answer 1

You are using a POSIX BRE regex engine with the \\_?\\s\\_? pattern that matches a _? , a whitespace (if your sed supports \\s shorthand) an a _? substring, ie the ? are treated as literal question mark symbols.

You may use

sed -E 's/[[:space:]_]+/_/g'
sed 's/[[:space:]_]\{1,\}/_/g'

See online sed demo

The [[:space:]_]+ POSIX ERE pattern (enabled with -E option) will match one or more whitespace or underscore characters.

The POSIX ERE + quantifier can be written as \\{1,\\} in POSIX BRE. Also, if you use a GNU sed , you may use \\+ in the second sed command.

Answer 2

This might work for you (GNU sed):

sed -E 's/\s(\s*_)*/_/g' file

This will replace a space followed by zero or more of the following: zero or more spaces followed by an underscore.