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Only one part of unicode character get deleted on backspace in WSL/bash (again) #12639

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opened 2026-01-31 03:20:54 +00:00 by claunia · 7 comments
claunia commented 2026-01-31 03:20:54 +00:00
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Originally created by @EugZol on GitHub (Feb 18, 2021).

Environment

Windows:

Platform ServicePack Version      VersionString
-------- ----------- -------      -------------
 Win32NT             10.0.19041.0 Microsoft Windows NT 10.0.19041.0

WSL2:

PS C:\Users\eugzol> bash -li
eugzol@DESKTOP-FAV7PTR:/mnt/c/Users/eugzol $ uname -a
Linux DESKTOP-FAV7PTR 4.19.128-microsoft-standard #1 SMP Tue Jun 23 12:58:10 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

Steps to reproduce

eugzol@DESKTOP-FAV7PTR:~ $ cat test.sh
read user_input
echo $user_input | xxd
eugzol@DESKTOP-FAV7PTR:~ $ chmod +x test.sh
eugzol@DESKTOP-FAV7PTR:~ $ ./test.sh
а
00000000: d0d0 b00a                                ....
eugzol@DESKTOP-FAV7PTR:~ $ bash -li test.sh
а
00000000: d0d0 b00a                                ....
eugzol@DESKTOP-FAV7PTR:~ $ echo $LANG
ru_RU.UTF-8

When running test_sh script above I enter а (lowercase Cyrillic letter), then press backspace, then enter а again, then press Enter.

Hex representation of the resultant string, as shown above, is d0 d0b0 0a. d0b0 is the correct representation of а. First d0 is the first byte of the а which was entered before pressing backspace. Second byte was deleted. Last 0a is the new line.

Expected behavior

Hex representation of the resultant string is d0b0 0a. That is, all bytes of the а symbol is deleted when pressing backspace.

Actual behavior

Backspace deletes only the last byte of two-byte symbol.

Originally created by @EugZol on GitHub (Feb 18, 2021). # Environment Windows: ``` Platform ServicePack Version VersionString -------- ----------- ------- ------------- Win32NT 10.0.19041.0 Microsoft Windows NT 10.0.19041.0 ``` WSL2: ``` PS C:\Users\eugzol> bash -li eugzol@DESKTOP-FAV7PTR:/mnt/c/Users/eugzol $ uname -a Linux DESKTOP-FAV7PTR 4.19.128-microsoft-standard #1 SMP Tue Jun 23 12:58:10 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux ``` # Steps to reproduce ``` eugzol@DESKTOP-FAV7PTR:~ $ cat test.sh read user_input echo $user_input | xxd eugzol@DESKTOP-FAV7PTR:~ $ chmod +x test.sh eugzol@DESKTOP-FAV7PTR:~ $ ./test.sh а 00000000: d0d0 b00a .... eugzol@DESKTOP-FAV7PTR:~ $ bash -li test.sh а 00000000: d0d0 b00a .... eugzol@DESKTOP-FAV7PTR:~ $ echo $LANG ru_RU.UTF-8 ``` When running `test_sh` script above I enter `а` (lowercase Cyrillic letter), then press backspace, then enter `а` again, then press Enter. Hex representation of the resultant string, as shown above, is `d0 d0b0 0a`. `d0b0` is the correct representation of `а`. First `d0` is the first byte of the `а` which was entered before pressing backspace. Second byte was deleted. Last `0a` is the new line. # Expected behavior Hex representation of the resultant string is `d0b0 0a`. That is, all bytes of the `а` symbol is deleted when pressing backspace. <!-- A description of what you're expecting, possibly containing screenshots or reference material. --> # Actual behavior <!-- What's actually happening? --> Backspace deletes only the last byte of two-byte symbol.
claunia commented 2026-01-31 03:20:55 +00:00
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@EugZol commented on GitHub (Feb 18, 2021):

#5057 was closed previously. Recommendations from that issue didn't help.

@EugZol commented on GitHub (Feb 18, 2021): #5057 was closed previously. Recommendations from that issue didn't help.
claunia commented 2026-01-31 03:20:55 +00:00
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@zadjii-msft commented on GitHub (Feb 18, 2021):

Out of curiosity, what's the value of LC_ALL? Sometimes that makes a difference

@zadjii-msft commented on GitHub (Feb 18, 2021): Out of curiosity, what's the value of `LC_ALL`? Sometimes that makes a difference
claunia commented 2026-01-31 03:20:55 +00:00
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@EugZol commented on GitHub (Feb 18, 2021):

Hm, it's empty:

 $ locale
LANG=ru_RU.UTF-8
LANGUAGE=
LC_CTYPE="ru_RU.UTF-8"
LC_NUMERIC="ru_RU.UTF-8"
LC_TIME="ru_RU.UTF-8"
LC_COLLATE="ru_RU.UTF-8"
LC_MONETARY="ru_RU.UTF-8"
LC_MESSAGES="ru_RU.UTF-8"
LC_PAPER="ru_RU.UTF-8"
LC_NAME="ru_RU.UTF-8"
LC_ADDRESS="ru_RU.UTF-8"
LC_TELEPHONE="ru_RU.UTF-8"
LC_MEASUREMENT="ru_RU.UTF-8"
LC_IDENTIFICATION="ru_RU.UTF-8"
LC_ALL=

If I set it manually, the error reproduces:

eugzol@DESKTOP-FAV7PTR:~ $ export LC_ALL=ru_RU.UTF-8
eugzol@DESKTOP-FAV7PTR:~ $ ./test.sh
а
00000000: d0d0 b00a                                ....
eugzol@DESKTOP-FAV7PTR:~ $ locale
LANG=ru_RU.UTF-8
LANGUAGE=
LC_CTYPE="ru_RU.UTF-8"
LC_NUMERIC="ru_RU.UTF-8"
LC_TIME="ru_RU.UTF-8"
LC_COLLATE="ru_RU.UTF-8"
LC_MONETARY="ru_RU.UTF-8"
LC_MESSAGES="ru_RU.UTF-8"
LC_PAPER="ru_RU.UTF-8"
LC_NAME="ru_RU.UTF-8"
LC_ADDRESS="ru_RU.UTF-8"
LC_TELEPHONE="ru_RU.UTF-8"
LC_MEASUREMENT="ru_RU.UTF-8"
LC_IDENTIFICATION="ru_RU.UTF-8"
LC_ALL=ru_RU.UTF-8

However, LC_ALL doesn't persist after I re-login to bash (even if I restart WSL), when I try to add it to /etc/default/local:

eugzol@DESKTOP-FAV7PTR:~ $ cat /etc/default/locale
LANG=ru_RU.UTF-8
LC_ALL=ru_RU.utf8
eugzol@DESKTOP-FAV7PTR:~ $ exit
выход
PS C:\Users\eugzol> bash
eugzol@DESKTOP-FAV7PTR:/mnt/c/Users/eugzol $ locale
LANG=ru_RU.UTF-8
LANGUAGE=
LC_CTYPE="ru_RU.UTF-8"
LC_NUMERIC="ru_RU.UTF-8"
LC_TIME="ru_RU.UTF-8"
LC_COLLATE="ru_RU.UTF-8"
LC_MONETARY="ru_RU.UTF-8"
LC_MESSAGES="ru_RU.UTF-8"
LC_PAPER="ru_RU.UTF-8"
LC_NAME="ru_RU.UTF-8"
LC_ADDRESS="ru_RU.UTF-8"
LC_TELEPHONE="ru_RU.UTF-8"
LC_MEASUREMENT="ru_RU.UTF-8"
LC_IDENTIFICATION="ru_RU.UTF-8"
LC_ALL=
@EugZol commented on GitHub (Feb 18, 2021): Hm, it's empty: ``` $ locale LANG=ru_RU.UTF-8 LANGUAGE= LC_CTYPE="ru_RU.UTF-8" LC_NUMERIC="ru_RU.UTF-8" LC_TIME="ru_RU.UTF-8" LC_COLLATE="ru_RU.UTF-8" LC_MONETARY="ru_RU.UTF-8" LC_MESSAGES="ru_RU.UTF-8" LC_PAPER="ru_RU.UTF-8" LC_NAME="ru_RU.UTF-8" LC_ADDRESS="ru_RU.UTF-8" LC_TELEPHONE="ru_RU.UTF-8" LC_MEASUREMENT="ru_RU.UTF-8" LC_IDENTIFICATION="ru_RU.UTF-8" LC_ALL= ``` If I set it manually, the error reproduces: ``` eugzol@DESKTOP-FAV7PTR:~ $ export LC_ALL=ru_RU.UTF-8 eugzol@DESKTOP-FAV7PTR:~ $ ./test.sh а 00000000: d0d0 b00a .... eugzol@DESKTOP-FAV7PTR:~ $ locale LANG=ru_RU.UTF-8 LANGUAGE= LC_CTYPE="ru_RU.UTF-8" LC_NUMERIC="ru_RU.UTF-8" LC_TIME="ru_RU.UTF-8" LC_COLLATE="ru_RU.UTF-8" LC_MONETARY="ru_RU.UTF-8" LC_MESSAGES="ru_RU.UTF-8" LC_PAPER="ru_RU.UTF-8" LC_NAME="ru_RU.UTF-8" LC_ADDRESS="ru_RU.UTF-8" LC_TELEPHONE="ru_RU.UTF-8" LC_MEASUREMENT="ru_RU.UTF-8" LC_IDENTIFICATION="ru_RU.UTF-8" LC_ALL=ru_RU.UTF-8 ``` However, `LC_ALL` doesn't persist after I re-login to bash (even if I restart WSL), when I try to add it to `/etc/default/local`: ``` eugzol@DESKTOP-FAV7PTR:~ $ cat /etc/default/locale LANG=ru_RU.UTF-8 LC_ALL=ru_RU.utf8 eugzol@DESKTOP-FAV7PTR:~ $ exit выход PS C:\Users\eugzol> bash eugzol@DESKTOP-FAV7PTR:/mnt/c/Users/eugzol $ locale LANG=ru_RU.UTF-8 LANGUAGE= LC_CTYPE="ru_RU.UTF-8" LC_NUMERIC="ru_RU.UTF-8" LC_TIME="ru_RU.UTF-8" LC_COLLATE="ru_RU.UTF-8" LC_MONETARY="ru_RU.UTF-8" LC_MESSAGES="ru_RU.UTF-8" LC_PAPER="ru_RU.UTF-8" LC_NAME="ru_RU.UTF-8" LC_ADDRESS="ru_RU.UTF-8" LC_TELEPHONE="ru_RU.UTF-8" LC_MEASUREMENT="ru_RU.UTF-8" LC_IDENTIFICATION="ru_RU.UTF-8" LC_ALL= ```
claunia commented 2026-01-31 03:20:56 +00:00
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@DHowett commented on GitHub (Feb 18, 2021):

So, there's one critical issue here ... and that's that we send bash (in any incarnation) a single backspace character (0x08/0x7f depending on encoding). That's by design: all terminals work like this. That's the only way it can be done: since the terminal cannot know how the receiving end will react to a backspace, it can't necessarily guess, for example, that it's going to delete one cell worth of data and send enough backspaces to destroy that cell.

@DHowett commented on GitHub (Feb 18, 2021): So, there's one critical issue here ... and that's that _we send bash (in any incarnation) a single backspace character (0x08/0x7f depending on encoding)_. That's by design: all terminals work like this. That's the only way it _can_ be done: since the terminal cannot know how the receiving end will react to a backspace, it can't necessarily guess, for example, that it's going to delete one cell worth of data and send enough backspaces to destroy that cell.
claunia commented 2026-01-31 03:20:56 +00:00
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@DHowett commented on GitHub (Feb 18, 2021):

However, you're right. There's something odd happening here. Both the Windows Console and Terminal do this differently than urxvt and Konsole on the same system/configuration.

image

@DHowett commented on GitHub (Feb 18, 2021): However, you're right. There's something odd happening here. Both the Windows Console and Terminal do this differently than urxvt and Konsole on the same system/configuration. ![image](https://user-images.githubusercontent.com/189190/108414450-17742500-71e1-11eb-8491-1849dc65409a.png)
claunia commented 2026-01-31 03:20:56 +00:00
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@mutax commented on GitHub (Apr 18, 2024):

The same can be seen when using input in ipython

#!/usr/bin/env python3
x = input("> ")
print(x)
print(len(x))

when removing one unicode character and replacing it using backspace it results in:

python3 getinput.py
> huhöäüöäxxx
huhöäüöä�xxx
12

This does not happen when using a different terminal, e.g. terminator, instead of the windows terminal.

@mutax commented on GitHub (Apr 18, 2024): The same can be seen when using `input ` in ipython ``` #!/usr/bin/env python3 x = input("> ") print(x) print(len(x)) ``` when removing one unicode character and replacing it using backspace it results in: ``` python3 getinput.py > huhöäüöäxxx huhöäüöä�xxx 12 ``` This does not happen when using a different terminal, e.g. terminator, instead of the windows terminal.
claunia commented 2026-01-31 03:20:56 +00:00
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@lhecker commented on GitHub (Apr 18, 2024):

However, you're right. There's something odd happening here. Both the Windows Console and Terminal do this differently than urxvt and Konsole on the same system/configuration.

I've looked into this today, and found that WSL indeed only uses GetConsoleInputW and that we return only the expected characters (U+0430 and U+007f) and nothing else. So it should theoretically not be a bug in conhost. I'm not sure how Linux and WSL handle line input in a VM like that, but I feel like it's not unlikely that this is a bug in WSL.

@lhecker commented on GitHub (Apr 18, 2024): > However, you're right. There's something odd happening here. Both the Windows Console and Terminal do this differently than urxvt and Konsole on the same system/configuration. I've looked into this today, and found that WSL indeed only uses `GetConsoleInputW` and that we return only the expected characters (U+0430 and U+007f) and nothing else. So it should theoretically not be a bug in conhost. I'm not sure how Linux and WSL handle line input in a VM like that, but I feel like it's not unlikely that this is a bug in WSL.
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Reference: starred/terminal#12639
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