The script should treat 'enter' as sending the users string but instead it just prints '^M' to the terminal.

I'm not sure why this is happening suddenly, it wasn't happening yesterday. Something has changed about this particular terminal session because if I open a new terminal window it works as expected in that.

Any ideas?

I'm using iterm on Mac (xterm?)

CodePudding user response：

TL;DR: just type the reset command on the OS shell whenever the terminal starts acting funny.

Terminal emulator programs (as iterm) feature complicated internal states in order to provide literally decades of features to allow prettier programs on the terminal.

Terminals started as keyboards that would physically print the typed text into paper, back in mainframe era - and "stdin" and "stdout" concepts: a single stream going forward with all data that is typed and another with all data that is printed out, are up to today, more than 50 years later, the default way to interact with the text terminal.

Internal state changes by programs that deal with the terminal in different ways (like being able to read a keypress without waiting for "enter"), should be reverted when the programs terminate. But due to errors and bugs that is not always the case.

I don't know which possible state would change "ˆM" to be displayed instead of a CR code being applied to the terminal. There are tens or hundreds of other possible misbehaviors, including completely messing up all characters. The reset command in modern *nixes (MacOS, Linux, BSDs) will fix everything.

Although, of course, if "enter" is not being applied, it won't be possible to issue the command at all from the os shell. You will have to start a new terminal session then. From within a Python program, if you happen to make a call to some code that will always break the terminal, you might run "reset" as a subprocess by calling os.system('reset').

In particular, "ˆM" represents "ctrl M", which is a control character with value "13" (0x0d in hex). It is the value for the "Carriage Return" control code (AKA. "return", "enter", "CR"). If you never did this: try pressing "ctrl M", and see that it behaves the same as "enter". It is being displayed in "human readable form" instead of acting as a control character in your case.

(regarding xterm and iterm: all they have in common is that they are both "terminal emulator" programs, xterm being one of the oldest existing such programs, which probably pioneered a lot of adaptations from text-only video modes to a graphic environment. "iterm" is just a normal modern app which implements terminal functionality)