Это один из тех вопросов, где полезно иметь тестовый входной файл и примеры желаемого вывода.

Входной файл

Вот тестовый входной файл, который я скопировал из Интернет и модифицирован для помещения поисковых слов в пары **:

$ cat ~/Downloads/wordlist.txt
**Schadenfreude**
This is a German word, although used in English too, which is used to mean ‘malicious enjoyment of the misfortunes of others’. It comes from the joining of the words schaden meaning ‘harm’ and freude meaning ‘joy’.

**Waldeinsamkeit**
Ever found yourself wandering alone through a forest and wanting to express the emotion brought about by that wander? Look no further! In German, Waldeinsamkeit means ‘woodland solitude’.

**L’esprit de l’escalier**
We all know the feeling of walking away from an argument and instantly thinking of the ideal comeback, or leaving a conversation and remembering the perfect contribution to a no-longer relevant subject. In French, l’esprit de l’escalier is the term used to refer to that irritating feeling. It literally translates as ‘the spirit of the staircase’, more commonly known as ‘staircase wit’. It comes from the idea of thinking of a response as you’re leaving somebody’s house, via their staircase.

**Schlimazel**
The Mr Men series of books by Roger Hargreaves is a staple of many a British child’s bookshelves, and there is a word which could have been created for the character Mr Bump. Like Mr Bump, a Schlimazel is ‘a consistently unlucky, accident-prone person, a born loser’. It is a Yiddish word, coming from the Middle High German word slim meaning ‘crooked’ and the Hebrew mazzāl meaning ‘luck’.

**Depaysement**
Ever go on holiday, only to experience a strange sensation of disorientation at the change of scenery? Dépaysement is a French word which refers to that feeling of disorientation that specifically arises when you are not in your home country.

**Duende**
This Spanish term implies something magical or enchanting. It originally referred to a supernatural being or spirit  similar to an imp or pixie (and is occasionally borrowed in that sense into English with reference to Spanish and Latin American folklore). Now, it has adapted to refer to the spirit of art or the power that a song or piece of art has to deeply move a person.

**Torschlusspanik**
Are you getting older? Scared of being left behind or ‘left on the shelf’? This British idiom has its own word in German: Torschlusspanik, which literally translates as ‘panic at the shutting of a gate’, is used frequently in a general sense meaning ‘last –minute panic’, of the type you might experience before a deadline.

*Do*Not*Return*these four star lines
*word***
***word*
word**

Использование grep

Используя grep, довольно просто получить список слов: [!d4 ]

$ grep -E -o '\*\*[^*]{,20}\*\*' ~/Downloads/wordlist.txt
**Schadenfreude**
**Waldeinsamkeit**
**L’esprit de l’escalier**
**Schlimazel**
**Depaysement**
**Duende**
**Torschlusspanik**

Если вы хотите удалить **, обменивая слова, добавьте канал в sed:

$ grep -E -o '\*\*[^*]{,20}\*\*' ~/Downloads/wordlist.txt | sed 's/*//g'
Schadenfreude
Waldeinsamkeit
L’esprit de l’escalier
Schlimazel
Depaysement
Duende
Torschlusspanik

Сохранение индекса слов в файл

7] Если вы хотите сохранить выходные данные grep и sed, используйте команду переназначения файла >:

$ grep -E -o '\*\*[^*]{,20}\*\*' ~/Downloads/wordlist.txt | sed 's/*//g' > ~/Downloads/wordlist-index.txt

$ cat ~/Downloads/wordlist-index.txt
Schadenfreude
Waldeinsamkeit
L’esprit de l’escalier
Schlimazel
Depaysement
Duende
Torschlusspanik

Примечание. Первоначальный ответ опубликован вчера с новым сообщением сегодня от muru на отдельном Q & amp; A: Использовать указанный квантификатор в grep для получения удовлетворенного словаря