Re: New utility suggestion: chdir(1)

[Pádraig Brady]

On 28/08/17 16:08, Bernhard Voelker wrote:
> On 08/27/2017 09:23 AM, Colin Watson wrote:
>> From 0a74257b9fb7e02587b6c5553d8bc1b536249a7e Mon Sep 17 00:00:00 2001
>> From: Colin Watson <address@hidden>
>> Date: Sun, 27 Aug 2017 08:16:21 +0100
>> Subject: [PATCH] env: add --chdir option
>>
>> This is useful when chaining with other commands that run commands in a
>> different context.
>>
>> * NEWS (New features): Document the new option.
>> * doc/coreutils.texi (env invocation): Likewise.
>> * src/env.c (usage): Likewise.
>> (main): Implement the new option.
>> * tests/misc/env.sh: Test the new option.
>> ---
>>  NEWS               |  3 +++
>>  doc/coreutils.texi | 17 +++++++++++++++++
>>  src/env.c          | 20 ++++++++++++++++++++
>>  tests/misc/env.sh  | 10 +++++++++-
>>  4 files changed, 49 insertions(+), 1 deletion(-)
>>
>> diff --git a/NEWS b/NEWS
>> index d37195e..60d5ca5 100644
>> --- a/NEWS
>> +++ b/NEWS
>> @@ -86,6 +86,9 @@ GNU coreutils NEWS                                    -*- 
>> outline -*-
>>  
>>    expr supports multibyte strings for all string operations.
>>  
>> +  env now has a --chdir option to change to a new working directory before
>> +  executing the subsidiary program.
>> +
> 
> To me (as non-native), "new working directory" might sound like the
> directory may be created at the same time, doesn't it?
> Maybe
>   s/to change to a new working directory/to change the working directory/
> ?

ack

>>  ** Improvements
>>  
>>    mv --verbose now distinguishes rename and copy operations.
>> diff --git a/doc/coreutils.texi b/doc/coreutils.texi
>> index 8f1cb4c..f127517 100644
>> --- a/doc/coreutils.texi
>> +++ b/doc/coreutils.texi
>> @@ -16909,6 +16909,23 @@ environment.
>>  @opindex --ignore-environment
>>  Start with an empty environment, ignoring the inherited environment.
>>  
>> +@item --chdir=@var{dir}
>> +@opindex --chdir
>> +Change the working directory to @var{dir} before invoking @var{command}.
>> +This differs from the shell built-in @command{cd} in that it starts
>> +@var{command} as a subprocess rather than altering the shell's own working
>> +directory; this allows it to be chained with other commands that run 
>> commands
>> +in a different context.  For example:
>> +
>> +@example
>> +# Run 'true' with /chroot as its root directory and /srv as its working
>> +# directory.
>> +chroot /chroot env --chdir=/srv true
>> +# Run 'true' with /build as its working directory, FOO=bar in its
>> +# environment, and a time limit of five seconds.
>> +env --chdir=/build FOO=bar timeout 5 true
>> +@end example
>> +
>>  @end table
>>  
>>  @cindex exit status of @command{env}
>> diff --git a/src/env.c b/src/env.c
>> index 63d5c2c..291fbb4 100644
>> --- a/src/env.c
>> +++ b/src/env.c
>> @@ -33,11 +33,19 @@
>>    proper_name ("Richard Mlynarik"), \
>>    proper_name ("David MacKenzie")
>>  
>> +/* For long options that have no equivalent short option, use a
>> +   non-character as a pseudo short option, starting with CHAR_MAX + 1.  */
>> +enum
>> +{
>> +  CHDIR = CHAR_MAX + 1
>> +};
>> +
>>  static struct option const longopts[] =
>>  {
>>    {"ignore-environment", no_argument, NULL, 'i'},
>>    {"null", no_argument, NULL, '0'},
>>    {"unset", required_argument, NULL, 'u'},
>> +  {"chdir", required_argument, NULL, CHDIR},
>>    {GETOPT_HELP_OPTION_DECL},
>>    {GETOPT_VERSION_OPTION_DECL},
>>    {NULL, 0, NULL, 0}
>> @@ -63,6 +71,7 @@ Set each NAME to VALUE in the environment and run 
>> COMMAND.\n\
>>    -i, --ignore-environment  start with an empty environment\n\
>>    -0, --null           end each output line with NUL, not newline\n\
>>    -u, --unset=NAME     remove variable from the environment\n\
>> +      --chdir=DIR      change working directory to DIR\n\
>>  "), stdout);
>>        fputs (HELP_OPTION_DESCRIPTION, stdout);
>>        fputs (VERSION_OPTION_DESCRIPTION, stdout);
>> @@ -81,6 +90,7 @@ main (int argc, char **argv)
>>    int optc;
>>    bool ignore_environment = false;
>>    bool opt_nul_terminate_output = false;
>> +  char const *newdir = NULL;
>>  
>>    initialize_main (&argc, &argv);
>>    set_program_name (argv[0]);
>> @@ -103,6 +113,9 @@ main (int argc, char **argv)
>>          case '0':
>>            opt_nul_terminate_output = true;
>>            break;
>> +    case CHDIR:
>> +      newdir = optarg;
>> +      break;
> 
> Please use tab-free indentation as throughout the whole coreutils
> sources.

ack (make syntax-check catches this)


>>          case_GETOPT_HELP_CHAR;
>>          case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
>>          default:
>> @@ -154,6 +167,13 @@ main (int argc, char **argv)
>>        usage (EXIT_CANCELED);
>>      }
>>  
>> +  if (newdir)
>> +    {
>> +      if (chdir (newdir) != 0)
>> +    die (EXIT_CANCELED, errno, _("cannot change directory to %s"),
>> +         quoteaf (newdir));
>> +    }
>> +
> 
> Likewise.
> 
>>    execvp (argv[optind], &argv[optind]);
>>  
>>    int exit_status = errno == ENOENT ? EXIT_ENOENT : EXIT_CANNOT_INVOKE;
>> diff --git a/tests/misc/env.sh b/tests/misc/env.sh
>> index f2f6ba8..c409630 100755
>> --- a/tests/misc/env.sh
>> +++ b/tests/misc/env.sh
>> @@ -18,7 +18,7 @@
>>  
>>  
>>  . "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
>> -print_ver_ env
>> +print_ver_ env pwd
>>  
>>  # A simple shebang program to call "echo" from symlinks like "./-u" or 
>> "./--".
>>  echo "#!$abs_top_builddir/src/echo simple_echo" > simple_echo \
>> @@ -150,4 +150,12 @@ test "x$(sh -c '\c=d echo fail')" = xpass && #dash 
>> 0.5.4 fails so check first
>>  returns_ 125 env -u a=b true || fail=1
>>  returns_ 125 env -u '' true || fail=1
>>  
>> +# Verify changing directory.
>> +mkdir empty || framework_failure_
>> +returns_ 125 env --chdir=empty/nonexistent true || fail=1
>> +curdir=$(env pwd) || fail=1
>> +test "$curdir" = "$(pwd)" || fail=1
> 
> The above does not run CU's version of pwd, but instead
> that of the shell.  The test therefore fails when "pwd -L"
> != "pwd -P" (and the implementation of coreutils and that
> of the shell differs).
> 
>> +curdir=$(env --chdir=empty pwd) || fail=1
>> +test "$curdir" = "$(cd empty && pwd)" || fail=1
>> +
>>  Exit $fail
>> -- 
> 
> I therefore propose to squash in the following change:
> 
> diff --git a/tests/misc/env.sh b/tests/misc/env.sh
> index c409630..7c864cd 100755
> --- a/tests/misc/env.sh
> +++ b/tests/misc/env.sh
> @@ -153,9 +153,8 @@ returns_ 125 env -u '' true || fail=1
>  # Verify changing directory.
>  mkdir empty || framework_failure_
>  returns_ 125 env --chdir=empty/nonexistent true || fail=1
> -curdir=$(env pwd) || fail=1
> -test "$curdir" = "$(pwd)" || fail=1
> -curdir=$(env --chdir=empty pwd) || fail=1
> -test "$curdir" = "$(cd empty && pwd)" || fail=1
> +exp=$(cd empty && env pwd) || framework_failure_
> +got=$(env --chdir=empty pwd) || fail=1

This is missing the `test`, but I'll change as you intended.

thanks!
Pádraig