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There is a good app "Termux" which can provide a powerful shell environment without gaining root permission. However, the touch-screen keyboard doesn't include the "Control" and "Alt" buttons. But some interactive programs (for example, nano, emacs) require these buttons.
Is there any way to add this button or use some other way to replace this button?
You will want to use Hackers Keyboard (available on Play Store as well as on F-Droid) for that, which was explicitly written for such purpose:
Hacker's Keyboard (source: Google Play; click image for larger variant)
That would be the most convenient approach – though the app hasn't been updated lately. But if you don't want that, just take a look at the corresponding Termux help page (or the matching Termux Wiki page): Termux utilizes the volume keys for "special combos". You can also have the most common keys shown on the screen to be "tap ready":
The docu writes: To enable the extra keys view you have to long tap on the keyboard button in the left drawer menu. You can also press Volume Up+Q.
Or, as Death Mask Salesman stated in a now deleted comment: "Volume Down equals Control, while Volume Up is the same as Alt."
When you slide on the left-hand side of the screen, you get two options:
Click and hold on the keyboard and all the essential keys will appear on your keyboard. That's all you have to do.
Press VOLUME UP+Q to enable and VOLUME UP+K to disable extra keys in termux.
To edit extra keys and shortcuts in termux
nano ~/.termux/termux.properties
and add save
extra-keys = [['ESC','/','-','HOME','UP','END','PGUP'],['TAB','CTRL','ALT','LEFT','DOWN','RIGHT','PGDN']]
You can include shortcuts you like by changing termux.properties.
Reference link
You can use Volume Down + C to get the same job.
