Find a string on one line and return the string directly below the found string - Python or UNIX

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I am having trouble coming up with a way to parse a file in python. The file has rows with random letters and characters (see below).


Given a string, e.g. 'BAD' return or print the characters immediately below it. For this file, the code should return:


Thanks for any assistance!

Here's what I've started with:

num_lines = sum(1 for line in open('file.txt'))
x = 0
while x <= num_lines:
    _str = lines[x]
    loc = _str.find('BAD')
    x = x+1
    _str = lines[x]
    print (_str[loc:loc+2]

You are close to the solution. Step through the pairs of lines, find the marker ("BAD") in the first and the word with the same index in the second:

marker = 'BAD'
marker_len = len(marker)

for l1, l2 in zip(lines, lines[1:]):
   i = l1.find(marker) # Find the first marker
   while i != -1: # Are there any more markers?
     print(l2[i:i + marker_len])
     i = l1.find(marker, i + marker_len) # Search the rest of l1
# #@@
# ##G

Python, a inbuilt function find() which checks if a substring is present in the string, which is done in one line. find() function returns -1 if it is not found, else it returns first  If the substring is not found, the find method will return -1. Meaning that the substring was not found in the parent string. If the substring is found, the find method will return the starting index of the first character of the substring.

A solution using re module:

import re

length = int(len(str)/len(str.split('\n')))
p = re.compile("BAD")
for m in p.finditer(str):
    i = m.start()+length
    j = m.end()+length
    print (str[i:j])



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Singleline using re:

import re

data = '''

print(re.findall(r'(?=(?:BAD))(?=(?:.{%s}(...)))' % (len(max(data.splitlines())) + 1), data, flags=re.DOTALL))


['#@@', '##G', 'MHT', 'HWA']

Explanation of this regexp here.

Search Multiple Words / String Pattern Using grep Command on , How do I search multiple strings or words using the grep command? Use single quotes in the pattern: grep 'pattern*' file1 file2; Next use extended Grep searching two words in a line Search all python files for 'wordA' or 'wordB' ### Get the latest tutorials on SysAdmin, Linux/Unix and open source  Now you can see that FIND brought up one line that matches the search string, which means it is working. Let’s try this again, but change the search string to “sushi”; if your results look like the image below, you did it right. Scenario 2 – Search multiple documents for the same string of words.

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  • str is a built-in datatype. Do not overwrite it.
  • Thanks! This works great! The l1, l2, and zip are completely new to me!
  • l1 and l2 are just variable names.
  • FWIW, You don't need to read all the lines. In fact, unless you can guarantee the input is small you shouldn't read all the lines up front. It is sufficient, and far more efficient, to do for l1, l2 in zip(f, f):.
  • Good to know. I'll adjust the script. Thanks!
  • What is the meaning of 26?
  • Yeah cheers, calculated the offset in the terminal but forgot to include it in the snippet. Edited the answer.