Bug 8956

Summary:	Sh outputs an extra control character
Product:	Busybox	Reporter:	Matthias Pall Gissurarson <icetritlo>
Component:	Website	Assignee:	unassigned
Status:	NEW ---
Severity:	minor	CC:	busybox-cvs
Priority:	P5
Version:	unspecified
Target Milestone:	---
Hardware:	All
OS:	Linux
Host:		Target:
Build:

Description Matthias Pall Gissurarson 2016-05-20 17:31:53 UTC

Greetings,

When I run sh with the parameters

exec env ENV='' HISTFILE=/dev/null PROMPT_COMMAND='' PS1=\#\$\  PS2='' PS3='' /bin/sh

instead of getting back the expected "#$ ", I get "#$ [6n" i.e. the control character "^[[6n" is appended to the output. This causes issues when using tramp and sh to edit files on busybox via emacs, since it tries to match the output with "#$ ". When the same is run on other shells (such as bash), the control character is not present.

This bug was discovered in alpine linux version 3.3.3, for which a docker container can be run via "docker run -it --rm --name alpine alpine sh", which will start the busybox shell.

Comment 1 Matthias Pall Gissurarson 2016-05-20 17:41:04 UTC

The bug is also reproducible in the busybox docker image,
runnable with "docker run -it --name busybox --rm busybox sh"

Comment 2 Matthias Pall Gissurarson 2016-05-27 14:11:03 UTC

So apparently this is caused by EDITING_ASK_TERMINAL

Comment 3 Denys Vlasenko 2016-05-28 19:25:02 UTC

(In reply to Matthias Pall Gissurarson from comment #2)
> So apparently this is caused by EDITING_ASK_TERMINAL

Yes. But sh (to be more precise, lineedit.c code) uses that _only_ if run on a tty.
Are you scraping tty output? Why?