Bug #121974 for Term-ANSIColor: colored doesn't reliably reset the color on STDERR

This was an *excellent* bug report. Thank you for the effort you put into it! "Andreas Schwarz via RT" <bug-Term-ANSIColor@rt.cpan.org> writes: Show quoted text
If you either enable autoflush on STDOUT ($| = 1) or set $Term::ANSIColor::EACHLINE to "\n", that will resolve this problem. This is sort of explained in the manual page, but doesn't explicitly mention interleaving STDOUT and STDERR or line buffering and should. I'll update the documentation before closing this out. But what's happening is the same thing described here: Normally, colored() just puts attribute codes at the beginning and end of the string, but if you set $Term::ANSIColor::EACHLINE to some string, that string will be considered the line delimiter and the attribute will be set at the beginning of each line of the passed string and reset at the end of each line. This is often desirable if the output contains newlines and you're using background colors, since a background color that persists across a newline is often interpreted by the terminal as providing the default background color for the next line. Programs like pagers can also be confused by attributes that span lines. Normally you'll want to set $Term::ANSIColor::EACHLINE to "\n" to use this feature. This line: Show quoted text
is actually printing the string: "\e[31mred STDOUT text\n\e[0m" STDOUT is line-buffered by default when connected to a terminal, which means that output is flushed after each newline. Perl therefore (via stdio) prints out: "\e[31mred STDOUT text\n" and then buffers "\e[0m" because it hasn't seen another newline. Therefore, this: Show quoted text
is displayed in red. You then print the rest of a line to STDOUT: Show quoted text
which flushes the buffer and resets the color. The reason why this works as expected in your next example is that you print another line to STDOUT first, which flushes the pending output and resets the color properly. Show quoted text
You don't see the same phenomenon with STDERR because STDERR is *not* line-buffered by default; by default, it's unbuffered, and Perl flushes the output after every bit of output. In general, I recommend setting autoflush on STDOUT at the start of any program that might mix STDOUT and STDERR output, since the line buffering can cause other weird problems and intermixed output. The only drawback is that it makes I/O much less efficient if you have a lot of STDOUT output and partial lines, but most programs that do this sort of mixing aren't performance-sensitive. -- #!/usr/bin/perl -- Russ Allbery, Just Another Perl Hacker $^=q;@!>~|{>krw>yn{u<$$<[~||<Juukn{=,<S~|}<Jwx}qn{<Yn{u<Qjltn{ > 0gFzD gD, 00Fz, 0,,( 0hF 0g)F/=, 0> "L$/GEIFewe{,$/ 0C$~> "@=,m,|,(e 0.), 01,pnn,y{ rw} >;,$0=q,$,,($_=$^)=~y,$/ C-~><@=\n\r,-~$:-u/ #y,d,s,(\$.),$1,gee,print