On 2025-07-26 18:33, Alan Coopersmith wrote:
A very old bug in the Solaris bug database, originally filed in 1994 against both SunOS 4.1.3_U1 and Solaris 2.3 claims that this is intentional behavior
Oh my, that's a blast from the past.Thanks, Farblos, for pointing out this gotcha. I installed the attached to document it, plus some other gotchas I noticed nearby.
You'd think cd would be simple but nooooo, it confused even its original inventors. See <https://www.nokia.com/bell-labs/about/dennis-m-ritchie/hist.html> and look for "chdir".
From b1eb59a78a0d5f1bdb10bc8869d5e48f73dcbc7a Mon Sep 17 00:00:00 2001 From: Paul Eggert <egg...@cs.ucla.edu> Date: Sun, 27 Jul 2025 10:29:42 -0700 Subject: [PATCH] doc: update cd info * doc/autoconf.texi: Modernize and update description of cd gotchas. Prompted by email from Farblos in: https://lists.gnu.org/r/autoconf/2025-07/msg00004.html --- doc/autoconf.texi | 39 +++++++++++++++++++++++++++++++++++++-- 1 file changed, 37 insertions(+), 2 deletions(-) diff --git a/doc/autoconf.texi b/doc/autoconf.texi index 78bbec03..c6b23c78 100644 --- a/doc/autoconf.texi +++ b/doc/autoconf.texi @@ -17145,6 +17145,12 @@ output via terminal escape sequences, and the result can cause spurious failures when the output is not directed to a terminal. Configure scripts use M4sh, which automatically unsets this variable. +@item HOME +@evindex HOME +Strange things can happen if @env{HOME} is unset or empty. +For example, plain @command{cd} (with no arguments) has unspecified behavior. +Also, @env{HOME} should be absolute, not relative. + @item IFS @evindex IFS Long ago, shell scripts inherited @env{IFS} from the environment, @@ -17380,6 +17386,12 @@ than 3.1.6-dev-18. If you are using an older @command{zsh} and forget to set @env{NULLCMD}, your script might be suspended waiting for data on its standard input. +@item OLDPWD +@evindex OLDPWD +POSIX requires that @command{cd} must update the @env{OLDPWD} +environment variable, if set, to point to the name of the previous +directory, but Solaris 10 @command{/bin/sh} does not support this. + @item options @evindex options For @command{zsh} 4.3.10, @env{options} is treated as an associative @@ -17860,8 +17872,26 @@ Also, Autoconf-generated scripts check for this problem when computing variables like @code{ac_top_srcdir} (@pxref{Configuration Actions}), so it is safe to @command{cd} to these variables. -POSIX states that behavior is undefined if @command{cd} is given an -explicit empty argument. Some shells do nothing, some change to the +POSIX specifies an @option{-e} option that affects the exit status +when the @option{-P} option is in effect. Portable scripts should +avoid it for the same reason they avoid @option{-P}. + +@evindex OLDPWD +@evindex PWD +POSIX says that a successful @command{cd} updates the values of the +@env{OLDPWD} and @env{PWD} variables, and that @command{cd -} acts like +@command{cd $OLDPWD}. Older shells, such as Solaris 10 +@command{/bin/sh}, do not support this and portable scripts should not +rely on it. + +@evindex HOME +If @env{HOME} is unset or empty, the behavior of @command{cd} with no +arguments is implementation-defined, so portable scripts should avoid it +in that case. + +POSIX 1003.1-2024 states that @command{cd} must fail if given an +explicit empty argument. However, earlier POSIX editions did not +specify the behavior and some shells do nothing, some change to the first entry in @env{CDPATH}, some change to @env{HOME}, and some exit the shell rather than returning an error. Unfortunately, this means that if @samp{$var} is empty, then @samp{cd "$var"} is less predictable @@ -17870,6 +17900,11 @@ at changing to @env{HOME}, although this is probably not what you wanted in a script). You should check that a directory name was supplied before trying to change locations. +If @command{cd} fails, POSIX requires the invoking shell to behave as if +@command{cd} exited with status 1, which means the invoking shell can continue. +However, Solaris 10 @command{/bin/sh} aborts the containing command if +interactive, and exits otherwise. + @xref{Special Shell Variables}, for portability problems involving @command{cd} and the @env{CDPATH} environment variable. Also please see the discussion of the @command{pwd} command. -- 2.48.1
