[FIXED] Why does the terminal show "^[[A" "^[[B" "^[[C" "^[[D" when pressing the arrow keys in Ubuntu?

Issue

I've written a tiny program in Ansi C on Windows first, and I compiled it on Ubuntu with the built-in GCC now.

The program is simple:

• read the line from console with scanf().
• Analyze the string and calculate.

But something weird happens. When I try to move the cursor, it prints four characters:

• pressing Up prints "^[[A"
• pressing Dn prints "^[[B"
• pressing Rt prints "^[[C"
• pressing Lt prints "^[[D"

• How can this be avoided?

• Why does it print these 4 characters instead of moving the cursor?

Solution

Because that's what the keyboard actually sends to the PC (more precisely, what the terminal prints for what it actually receives from the keyboard). bash for example gets those values, deciphers them and understands that you want to move around, so it will either move the cursor (in case of left/right) or use its history to fetch previous commands (up/down). So you can't expect your program to magically support arrow keys.

However, reading from standard input from the terminal already supports left/right arrow keys (I believe, but I'm not in Linux right now to test and make sure). So my guess is that there is another issue interfering. One possible cause could be that one of your modifier keys is stuck? Perhaps ALT, CTRL or SUPER?

Answered By - Shahbaz

Answer Checked By - David Marino (PHPFixing Volunteer)