在一行中查找字符串，然后在找到的字符串的正下方返回该字符串- Python或UNIX

def find_string_below(string, target):
    index = string.find(target)
    if index != -1:
        lines = string.split('\n')
        if index + 1 < len(lines):
            return lines[index + 1]
    return None

# 示例用法
text = '''
This is line 1.
This is line 2.
This is line 3.
This is line 4.
This is line 5.
'''

target_string = 'line 3'
result = find_string_below(text, target_string)
print(result)

This is line 4.

grep -A 1 'target_string' file.txt