bash – 如何创建文件中每个单词的频率列表？

我有一个这样的文件：

This is a file with many words.
Some of the words appear more than once.
Some of the words only appear one time.

我想生成一个两列列表。第一列显示出什么词，第二列显示出现的频率，例如：

this@1
is@1
a@1
file@1
with@1
many@1
words3
some@2
of@2
the@2
only@1
appear@2
more@1
than@1
one@1
once@1
time@1

>为了使此工作更简单，在处理列表之前，我将删除所有标点符号，并将所有文本更改为小写字母。
>除非有一个简单的解决方案，单词和单词可以算作两个单独的单词。

到目前为止，我有这个：

sed -i "s/ /\n/g" ./file1.txt # put all words on a new line
while read line
do
     count="$(grep -c $line file1.txt)"
     echo $line"@"$count >> file2.txt # add word and frequency to file
done < ./file1.txt
sort -u -d # remove duplicate lines

由于某些原因，这只是在每个单词之后显示“0”。

如何生成文件中显示的每个单词列表以及频率信息？

不是sed和grep，而是tr，sort，uniq和awk：

% (tr ' ' '\n' | sort | uniq -c | awk '{print $2"@"$1}') <<EOF
This is a file with many words.
Some of the words appear more than once.
Some of the words only appear one time.
EOF

a@1
appear@2
file@1
is@1
many@1
more@1
of@2
once.@1
one@1
only@1
Some@2
than@1
the@2
This@1
time.@1
with@1
words@2
words.@1