Re: [PATCH] printenv: add feature to print names only

[Pádraig Brady]

On 11/12/2022 17:07, Gianluca Mascolo wrote:
> > From 0ed502c97c5b1dd51dc323e3f1354db99d1ab46f Mon Sep 17 00:00:00 2001
> From: Gianluca Mascolo <gianluca@gurutech.it>
> Date: Sun, 11 Dec 2022 18:02:20 +0100
> Subject: [PATCH] printenv: add feature to print names only
>
> ---
>   src/printenv.c         | 13 +++++++++++--
>   tests/misc/printenv.sh |  3 +++
>   2 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/src/printenv.c b/src/printenv.c
> index 0b178bedd..47eff3c91 100644
> --- a/src/printenv.c
> +++ b/src/printenv.c
> @@ -47,6 +47,7 @@ enum { PRINTENV_FAILURE = 2 };
>   static struct option const longopts[] =
>   {
>     {"null", no_argument, NULL, '0'},
> +  {"names-only", no_argument, NULL, 'n'},
>     {GETOPT_HELP_OPTION_DECL},
>     {GETOPT_VERSION_OPTION_DECL},
>     {NULL, 0, NULL, 0}
> @@ -68,6 +69,7 @@ If no VARIABLE is specified, print name and value pairs for 
> them all.\n\
>                 program_name);
>         fputs (_("\
>     -0, --null     end each output line with NUL, not newline\n\
> +  -n, --names-only     output only variable name, not value\n\
>   "), stdout);
>         fputs (HELP_OPTION_DESCRIPTION, stdout);
>         fputs (VERSION_OPTION_DESCRIPTION, stdout);
> @@ -86,6 +88,7 @@ main (int argc, char **argv)
>     bool ok;
>     int optc;
>     bool opt_nul_terminate_output = false;
> +  bool opt_names_only = false;
>   
>     initialize_main (&argc, &argv);
>     set_program_name (argv[0]);
> @@ -96,13 +99,16 @@ main (int argc, char **argv)
>     initialize_exit_failure (PRINTENV_FAILURE);
>     atexit (close_stdout);
>   
> -  while ((optc = getopt_long (argc, argv, "+iu:0", longopts, NULL)) != -1)
> +  while ((optc = getopt_long (argc, argv, "+iu:0n", longopts, NULL)) != -1)
>       {
>         switch (optc)
>           {
>           case '0':
>             opt_nul_terminate_output = true;
>             break;
> +        case 'n':
> +          opt_names_only = true;
> +          break;
>           case_GETOPT_HELP_CHAR;
>           case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
>           default:
> @@ -113,7 +119,10 @@ main (int argc, char **argv)
>     if (optind >= argc)
>       {
>         for (env = environ; *env != NULL; ++env)
> -        printf ("%s%c", *env, opt_nul_terminate_output ? '\0' : '\n');
> +        printf ("%.*s%c",
> +                opt_names_only ? ((int) (strchr(*env,'=') - *env)) : ((int) 
> strlen(*env)),
> +                *env,
> +                opt_nul_terminate_output ? '\0' : '\n');
>         ok = true;
>       }
>     else
> diff --git a/tests/misc/printenv.sh b/tests/misc/printenv.sh
> index 6cee5e7de..d97277fa1 100755
> --- a/tests/misc/printenv.sh
> +++ b/tests/misc/printenv.sh
> @@ -58,6 +58,9 @@ b
>   EOF
>   compare exp out || fail=1
>   
> +# Print only variable names
> +env -i ENV_TEST=hidden PATH="$PATH" printenv | grep -qF hidden && fail=1
> +
>   # Exit status reflects missing variable, but remaining arguments processed.
>   export ENV_TEST1=a
>   returns_ 1 env -- printenv ENV_TEST2 ENV_TEST1 > out || fail=1


This has some merit,
given that's it's awkward to postprocess printenv output
in the presence of multiline env values.

Could you detail some use cases for this?

thanks,
Pádraig