Reline emits extra escape sequences when stdin/stdout/stderr are not TTY

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#886 opened on Mar 7, 2026 5 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 4/5
Estimated time: 3-5 days
Newbie friendliness: 68/100

Issue type: Bug
Clarity: Mostly clear
Activity status: Active
Tech stack: ruby
Domain: cli

Research direction

Start with the reported Readline.readline reproduction using redirected stdin, stdout, and stderr, then compare its output with readline-ext. Review the linked TruffleRuby can-we-fold-yet test and expected.txt to define the non-TTY result. Done means Reline emits no terminal escape sequences when all three streams are not TTYs, while preserving interactive behavior.

Written by the indexing model from the issue text.

Description

Reline 0.6.0 from Ruby 3.4.7 (same with reline 0.6.3 the last release):

$ echo 'my input' > in
$ ruby -rreadline -e 'p Readline; p [STDIN,STDOUT,STDERR].map(&:tty?); p Readline.readline("> ", true)' < in |& ruby -e 'p STDIN.read'            
"Reline\n[false, false, false]\n> \e[?25l\e[1G\e[K\e[1G\e[0m> \e[0m\e[?25h\e[3G\e[?25l\e[1G\e[K\e[?25h\e[1G> my input\r\n\e[1G\"my input\"\n"

Even though STDIN, STDOUT, STDERR are all not TTY, terminal escape sequences are still included.
This causes issues for e.g. this program using Readline.readline because it's supposed to work well both if TTY or not. If not TTY, it expects no escape sequences.
That works with Readline from readline-ext but not Reline (as-is at least).

TERM=dumb doesn't help, it outputs many extra things (#660):

$ TERM=dumb ruby -rreadline -e 'p Readline; p [STDIN,STDOUT,STDERR].map(&:tty?); p Readline.readline("> ", true)' < in |& ruby -e 'p STDIN.read' 
"Reline\n[false, false, false]\n> > mmymy my imy inmy inpmy inpumy input> my input\r\n\"my input\"\n"

readline-ext for comparison works fine:

$ gem i readline-ext  
$ ruby -rreadline -e 'p Readline; p [STDIN,STDOUT,STDERR].map(&:tty?); p Readline.readline("> ", true)' < in |& ruby -e 'p STDIN.read'
"Readline\n[false, false, false]\n> my input\n\"my input\"\n"

Is there a way to achieve the same with Reline?

Dominant language: Ruby
Stars: 311
Forks: 99
Avg merge: 6d 4h
Merged PRs (30d): 1

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