Adding lines after specific line
This is what I did.
def find_append_to_file(filename, find, insert):
"""Find and append text in a file."""
with open(filename, 'r+') as file:
lines = file.read()
index = repr(lines).find(find) - 1
if index < 0:
raise ValueError("The text was not found in the file!")
len_found = len(find) - 1
old_lines = lines[index + len_found:]
file.seek(index)
file.write(insert)
file.write(old_lines)
# end find_append_to_file
You cannot safely write to a file while reading, it is better to read the file into memory, update it, and rewrite it to file.
with open("file.txt", "r") as in_file:
buf = in_file.readlines()
with open("file.txt", "w") as out_file:
for line in buf:
if line == "; Include this text\n":
line = line + "Include below\n"
out_file.write(line)
Use sed
:
$ sed '/^include below/aincluded text' < file.txt
Explanation:
/^include below/
: matches every line that starts (^
) withinclude below
a
: appends a newline and the following textincludeed text
: the text thata
appends
Edit: Using Python:
for line in open("file.txt").readlines():
print(line, end="")
if line.startswith("include below"):
print("included text")