Output of git checkout goes to stderr

Output of git checkout goes to stderr

[Sayooj Surendran]

Hi,
Noticed that the output of git checkout command is going to stderr
channel. Is this an intended behaviour?
git version: 2.45.2
terminal output:

❯ git checkout -b test > stdout.txt 2> stderr.txt
❯ cat stdout.txt
❯ cat stderr.txt
Switched to a new branch 'test'

Re: Output of git checkout goes to stderr

[Eric Sunshine]

On Tue, Jul 30, 2024 at 1:44 AM Sayooj Surendran
<sayooj.surendran@bigbinary.com> wrote:
> Noticed that the output of git checkout command is going to stderr
> channel. Is this an intended behaviour?

Yes, it is intentional. Git's Documentation/CodingGuidelines has this to say:

--- >8 ---
Program Output

 We make a distinction between a Git command's primary output and
 output which is merely chatty feedback (for instance, status
 messages, running transcript, or progress display), as well as error
 messages. Roughly speaking, a Git command's primary output is that
 which one might want to capture to a file or send down a pipe; its
 chatty output should not interfere with these use-cases.

 As such, primary output should be sent to the standard output stream
 (stdout), and chatty output should be sent to the standard error
 stream (stderr). Examples of commands which produce primary output
 include `git log`, `git show`, and `git branch --list` which generate
 output on the stdout stream.

 Not all Git commands have primary output; this is often true of
 commands whose main function is to perform an action. Some action
 commands are silent, whereas others are chatty. An example of a
 chatty action commands is `git clone` with its "Cloning into
 '<path>'..." and "Checking connectivity..." status messages which it
 sends to the stderr stream.

 Error messages from Git commands should always be sent to the stderr
 stream.
--- >8 ---

Re: Output of git checkout goes to stderr

[Karthik Nayak]

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Sayooj Surendran <sayooj.surendran@bigbinary.com> writes:

Hello,

> Hi,
> Noticed that the output of git checkout command is going to stderr
> channel. Is this an intended behaviour?
> git version: 2.45.2
> terminal output:
>
> ❯ git checkout -b test > stdout.txt 2> stderr.txt
> ❯ cat stdout.txt
> ❯ cat stderr.txt
> Switched to a new branch 'test'

Thanks for reporting, this seems to be as expected. Note that all
chatty feedback is routed to stderr in Git.

This is also documented in 'Documentation/CodingGuidelines':

  We make a distinction between a Git command's primary output and
  output which is merely chatty feedback (for instance, status
  messages, running transcript, or progress display), as well as error
  messages. Roughly speaking, a Git command's primary output is that
  which one might want to capture to a file or send down a pipe; its
  chatty output should not interfere with these use-cases.

  As such, primary output should be sent to the standard output stream
  (stdout), and chatty output should be sent to the standard error
  stream (stderr). Examples of commands which produce primary output
  include `git log`, `git show`, and `git branch --list` which generate
  output on the stdout stream.

Thanks,
Karthik

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Re: Output of git checkout goes to stderr

[Junio C Hamano]

Sayooj Surendran <sayooj.surendran@bigbinary.com> writes:

> Noticed that the output of git checkout command is going to stderr
> channel. Is this an intended behaviour?

Show messages meant for human consumptions (not just errors and
warnings, but informational messages and eye-candy progress bars) to
the standard error stream, and using the standard output stream to
show what informational commands are asked to produce (e.g. running
"git status" would describe the status of the current working tree
to the standard output stream), is very much in line with the
original design we laid out in 2005 when Git was still very young,
and continues to be "intended" behaviour to this day.