grep -w 有什麼作用？

在這裡grep 與選項一起使用-w。我做了man grep並grep --help試圖找到上述選項的作用。兩個輸出都沒有說明-w選項。

該選項有什麼作用？為什麼它沒有出現在manor中--help？如果類似的事情再次發生，我還能在哪裡檢查答案？

我目前正在使用 Ubuntu，如果相關的話（是嗎？）

# grep --help | grep -e -w
 -w, --word-regexp         force PATTERN to match only whole words
 -H, --with-filename       print file name with output lines
 -L, --files-without-match  print only names of FILEs with no selected lines
 -l, --files-with-matches  print only names of FILEs with selected lines
# grep PRETTY /etc/os-release
PRETTY_NAME="Ubuntu 18.04 LTS"
# man grep | grep -e -w -A1
      -w, --word-regexp
             Select only those lines containing matches that form whole words.  The test is that the matching substring must either be at the beginning of the line, or preceded by a non-word constituent  character.   Similarly,  it
             must be either at the end of the line or followed by a non-word constituent character.  Word-constituent characters are letters, digits, and the underscore.

引用自：https://unix.stackexchange.com/questions/524828