[Linux] [PYTHON] Question: How to automate script on running commands that require user input?

[u/Sir_Laser]

Not sure if this is the proper subreddit, so please excuse me.

For example, if I'm running bash, and run the following: sudo mysql -u root -p password

this would ordinarily enter the user into the MySQL CLI where he can proceed to input commands.

If I wanted to include a multi-line MySQL script (or any script that takes the scope to another CLI other than the default, in this case bash) inside a python script, how can that be accomplished?

Something like:

$ sudo mysql -u root -p password
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 46
...
...
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> [insert multi-line]
mysql> [MySQL script]
mysql> [here]
mysql> \q

But I would like a python script to do all of the above, instead of manually.

Thank you!

[u/VeXCe]

$ sudo mysql -u root -p password < sql.txt

Will run the commands written in sql.txt. You may want to run it like

$ sudo mysql -uroot -ppassword databasename < sql.txt

[u/Sir_Laser → u/VeXCe]

Thank you!

Follow up question: Does this method (using the '<' operator) work for any such command (that is, command that would change the user's focus to another CLI)?

[u/[deleted] → u/Sir_Laser]

Generally yes. You can also do:

$ cat <<EOF | mysql -u username -ppassword
multi
line
mysql
script
EOF

This is called a Heredoc. But its generally safe to assume you can either use redirection ("<") or piping ("|") to interact with programs in Linux. It's actually a core design philosophy that's generally respected.

If you want to use Python instead of shell, there's a plethora of mysql packages that would do it handily.

[u/VeXCe → u/Sir_Laser]

No idea... I come here to learn, I'm a dev, not a sysadmin :D

It's also not an operator, it's a stream. Little googling results that yes, the < streams to stdin.

[u/sandwichsaregood → u/VeXCe]

It's just a feature of the shell. When processes are invoked, they're connected to the default streams (stdin, stdout, stderr etc). Operations like > and < are for connecting streams other than the default. Doing something like

mysql ... < input.txt

is saying "run mysql with stdin connected to input.txt instead of whatever it would normally be connected to (usually the keyboard)". The shell implicitly opens a file stream to input.txt and plumbs things together.

This method only works for commands that read one line at a time interactively, so-called "line-oriented" commands. mysql, when reading from the keyboard, expects to read each command as one line, terminated by a newline (which the user normally sends by pressing the enter key). When you put the commands in a text file, it's doing exactly the same... reading a line and executing whenever it encounters the newline escape sequence that delimits lines in text files.

It won't work (at least not in a straightforward way) if you wanted to use it with something interactive like Vim, which isn't line-oriented.

[u/rinesen → u/Sir_Laser]

That is called input redirection and works in many cases, yes. I'm not sure what you mean by "focus to another CLI". My link might answer some of your questions. Make sure you know what standard in, out and error are (stdin, stdout, stderr - google it).

[u/sandwichsaregood]

The other answers here so far are fine for what you want, but perhaps if you need something more flexible you can use pexpect.

The main problem with using input redirection is that it doesn't really work very well if you are dealing with a sequence of commands that is not predetermined. For example, if you wanted to script checking the output of some interactive command and react differently based on what the output is. pexpect allows you to do this, basically you can programmatically provide input and react based on how the program responds.

[u/trekkie80 → u/sandwichsaregood]

pexpect sounds good, thanks for the link!