通过python子进程运行搜索并用sed替换，导致字符不可见

Question

Given the file /tmp/hi with content: bali=${hi

and running the command on it sed -i -E 's/(^|[^.])hi/\\1bi/g' /tmp/hi

results in the following content in bali=${bi as expected.

However, running the sed command inside python3.5 subprocess:

import subprocess
subprocess.run("sed -i -E 's/(^|[^.])hi/\1bi/g' /tmp/hi", shell=True)

results in the following content:

inspected the file in vi and it shows: bali=$^Abi

Why does it happen and how to achieve the same file content using python3.5 subprocess?

Answer 1

That's because the \\1 is being interpreted by Python. You need to use raw string syntax ( r"some \\1 string with escape sequences" ) if you want to use escape sequences without having to escape them:

Python 3.5.3 (default, Jan 19 2017, 14:11:04)
[GCC 6.3.0 20170118] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> print("sed -i -E 's/(^|[^.])hi/\1bi/g' /tmp/hi")
sed -i -E 's/(^|[^.])hi/bi/g' /tmp/hi
>>> print(r"sed -i -E 's/(^|[^.])hi/\1bi/g' /tmp/hi")
sed -i -E 's/(^|[^.])hi/\1bi/g' /tmp/hi