如何使用sed查找和替换特定字符之前或之后的项目？

Question

我如何限制查找和替换以替换项目,但如果紧接在它之前的字符是"A","B"或"C"或紧跟在它之后的字符是"X","Y"或"Z"则不能".例如,给定这些输入行,如果要用"pet"替换"cat"替换:

• "有一只猫." →"这些是宠物."
• "有Acat." 没有变化,因为之前找到了"A".
• "有猫咪." 没有变化,因为"Y"是在之后发现的.
• "有CcatX." 没有变化,因为之前找到"C",之后找到"X".

Answer 1

假设您的文本位于名为text.txt. 这将起作用：

sed -i 's/\(.*[^ABC]\|^\)cat\([^XYZ].*\|$\)/\1pet\2/g' text.txt

发生了什么（来自tutorialspoint.com、man sed和sed regex）：

-i         Edit files in place (makes backup if extension supplied)
s/???/???/ Or s/regexp/replacement/, Attempt to match regexp against the pattern space.
/          Field separator to 's'.
^          Match first character on line.
\(         Start back reference.
.          Match any character.
[^ABC]     Do not match any charcter (^ = don't) in this list.
\|         Matches regex1 or regexp2 (do not match ABC or match start of line).
\)         End back reference.
cat        Match cat
\1         The first back reference.
\2         The second back reference.
g          Replace all matches, not just the first match.