使用 echo 写入文件的换行符在 shell 中有效，但在 Python 3 中为文字

Question

I'm on a Ubuntu 20.04 system, and I'm using Python 3.8 to write a script that does multiple things using configurable lines of bash, but one of them is that it creates desktop shortcuts.

This single-line command creates a desktop shortcut, and works flawlessly when I execute it directly in my terminal :

echo "[Desktop Entry]"$'\n'"Type=Application"$'\n'"Name[en_US]=Documents"$'\n'"Exec=pcmanfm ~/Documents"$'\n'"Icon=system-file-manager" > ~/Desktop/1;

However, when I execute it in Python, like so:

foobar.py

rl = """echo "[Desktop Entry]"$'\n'"Type=Application"$'\n'"Name[en_US]=Documents"$'\n'"Exec=pcmanfm ~/Documents"$'\n'"Icon=system-file-manager" > ~/Desktop/1;"""
subprocess.run(rl, shell=True)

...instead of creating a desktop shortcut with the proper name, icon, and action, it creates an empty file that contains the following text :

0.txt :

[Desktop Entry]$\nType=Application$\nName[en_US]=Sign Out$\nExec=/home/agent/QaSC/login/login.bin$\nIcon=system-switch-user

Is there any particular reason why Python would be handling the newline characters differently than the bash shell does, and if so, how can I resolve this problem?

Answer 1

$'...' is a bash extension, but the default shell used when shell=True is specified is sh . Use the executable option to specify an alternate shell.

subprocess.run(rl, shell=True, executable='/bin/bash')

Answer 2

Since the argument to echo has quotes, it could contain literal newlines at the command line, and therefore also in the Python process. I see no reason to use the Bash extension $'\n' syntax.

$ echo "foo
> bar"
foo
bar
$ python
Python 3.8.10 (default, Mar 15 2022, 12:22:08) 
[GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import subprocess
>>> subprocess.run('echo "foo\nbar"', shell=True)
foo
bar
CompletedProcess(args='echo "foo\nbar"', returncode=0)
>>> 

(It's also unclear why the Python code doesn't just write a file in the normal way, but I assume the command in the OP is essentially a placeholder.)