Extract column starting with uppercase followed by next column starting with lower case

Question

I have a file with multiple columns, separated by an underscore (_).

Most of the columns started with an uppercase for the first character, some with lower case.

I am intended to extract the string for each line, which begins with an upper case and the next column started with a lower case. There will be at least one such case happened for every line. (Update: It would be great to have only the first match). The tricky part is that the case doesn't happen at the same column for every line.

For example:

Today_is_a_Good_Day
It_Doesnt_rain
i_dont_Like_rainy_day

Desired output:

Today_is
Doesnt_rain
Like_rainy

Is there any way to do such text extraction using grep/sed/awk or other command?

I was trying to look for some similar solution to my problem but failed to find one.

Update: There will be at least

Answer 1

With a grep implementation with PCRE support and -o:

$ grep -P -o '(?<![^_])\p{Lu}[^_]*_\p{Ll}[^_]*' < your-file
Today_is
Doesnt_rain
Like_rainy

(you can replace grep -P with pcregrep if your grep doesn't support -P).

That's an uppercase Letter followed by 0 or more non-_s, followed by _, a lowercase Letter and another sequence of 0 or more non-_s, the whole thing only matching provided it doesn't follow a non-_ (that is, follows a _ or the start of the line).

That will print every matching occurrence on its own line. To limit it to the first match on each line, you could take a different approach:

grep -P -o '^(.*?_)??\K\p{Lu}[^_]*_\p{Ll}[^_]*' < your-file

For the last match on each line, the same but using the greedy version of the operators for the part that eats away the leading part:

grep -P -o '^(.*_)?\K\p{Lu}[^_]*_\p{Ll}[^_]*' < your-file

Answer 2

$ grep -o '[[:upper:]][[:alpha:]]*_[[:lower:]][[:alpha:]]*' file
Today_is
Doesnt_rain
Like_rainy

This pulls out any string that starts with an uppercase letter followed by any number of alphabetical characters, then an underscore followed by a lowercase letter and (possibly) more alphabetical characters.

The above would however pull out multiple matches per line, if there were multiple matches.

The following sed command does not have that issue (it would instead pull out the last such string on each line):

$ sed -n 's/.*\([[:upper:]][[:alpha:]]*_[[:lower:]][[:alpha:]]*\).*/\1/p' file
Today_is
Doesnt_rain
Like_rainy

Answer 3

An awk approach

awk -F'_' -v OFS='_' '{
    for (i=1; i<NF; i++) {
        if ($i ~ /^[[:upper:]]/ && $(i+1) ~ /^[[:lower:]]/) {
            print $i, $(i+1)
            break
        }
    }
}' file

The break ensures that only the first match is printed.

Answer 4

sed 's/.*\([A-Z][^_]*_[a-z][^_]*\).*/\1/' <your-file

EDIT: greedy sed give the last match. awk solution for first match:

awk '{match($0,/([A-Z][^_]*_[a-z][^_]*)/,a); print a[1]}' <your-file