grep - 提取所选字母的相邻字符

Question

我有这个文本文件:

# cat letter.txt
this
is
just
a
test
to
check
if
grep
works

字母“e”出现在3个单词中。

# grep e letter.txt
test
check
grep

有没有办法返回打印在所选字符左侧的字母？

expected.txt
t
h
r

Answer 1

在 awk 中显示示例，请您尝试以下操作。

awk '/e/{print substr($0,index($0,"e")-1,1)}' Input_file

说明: 为以上添加详细说明。

awk '             ##Starting awk program from here.
/e/{              ##Looking if current line has e in it then do following.
  print substr($0,index($0,"e")-1,1)
                  ##Printing sub string from starting value of index e-1 and print 1 character from there.
}
' Input_file      ##Mentioning Input_file name here.