[PATCH] printenv: add feature to print names only

[Gianluca Mascolo]

>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
-- 
2.34.1