libtextstyle: Support the NO_COLOR environment variable.

bhaible · bhaible · commit 7040b13946b3 · 2019-08-14T02:46:36.000+02:00
It follows the specification at https://no-color.org/. The support is in the example programs, not in the function styled_ostream_create, so that it can be overridden through the command-line option --color=always. We only test whether the environment variable is set, not whether its value is non-empty. POSIX-specified environment variables are treated like unset when their value is empty; this is because in the old days it was not possible to unset an environment variable. But nowadays: - all shells support the 'unset' built-in, - all platforms that have the setenv() function also have the unsetenv() function, and - the 'env' program from GNU coreutils supports --unset=VARIABLE to unset a variable. This makes it possible to unset an environment variable that is set by the parent process. * libtextstyle/adhoc-tests/hello.c (main): Do not emit styling when the environment variable NO_COLOR is set. * libtextstyle/examples/color-filter/filter.c (main): Likewise. * libtextstyle/examples/color-hello/hello.c (main): Likewise. * gettext-tools/src/write-catalog.c (msgdomain_list_print): Likewise. * libtextstyle/doc/libtextstyle.texi (The NO_COLOR variable): New section. * libtextstyle/NEWS: Mention it.
diff --git a/gettext-tools/src/write-catalog.c b/gettext-tools/src/write-catalog.c
@@ -210,7 +210,9 @@ msgdomain_list_print (msgdomain_list_ty *mdlp, const char *filename,
 #if ENABLE_COLOR
   if (output_syntax->supports_color
       && (color_mode == color_yes
-          || (color_mode == color_tty && to_stdout && isatty (STDOUT_FILENO))))
+          || (color_mode == color_tty && to_stdout
+              && isatty (STDOUT_FILENO)
+              && getenv ("NO_COLOR") == NULL)))
     {
       int fd;
       ostream_t stream;
diff --git a/libtextstyle/NEWS b/libtextstyle/NEWS
@@ -1,3 +1,7 @@
+New in 0.21:
+* The example programs support the NO_COLOR environment variable,
+  as specified in https://no-color.org/.
+
 New in 0.20:
 * New class: noop_styled_ostream_t.
   New constructor function: noop_styled_ostream_create.
diff --git a/libtextstyle/adhoc-tests/hello.c b/libtextstyle/adhoc-tests/hello.c
@@ -56,7 +56,9 @@ main (int argc, char *argv[])
     }
 
   if (color_mode == color_yes
-      || (color_mode == color_tty && isatty (STDOUT_FILENO))
+      || (color_mode == color_tty
+          && isatty (STDOUT_FILENO)
+          && getenv ("NO_COLOR") == NULL)
       || color_mode == color_html)
     {
       /* If no style file is explicitly specified, use the default in the
diff --git a/libtextstyle/doc/libtextstyle.texi b/libtextstyle/doc/libtextstyle.texi
@@ -243,6 +243,7 @@ scroll around in the styled output.  For example:
 
 @menu
 * The TERM variable::
+* The NO_COLOR variable::
 * Emacs::
 * The --color option::
 * The --style option::
@@ -357,6 +358,19 @@ default @code{TERM=vt100}.
 
 On Windows consoles, no @code{TERM} setting is needed.
 
+@node The NO_COLOR variable
+@section The environment variable @code{NO_COLOR}
+
+@vindex NO_COLOR@r{, environment variable}
+@c The name of this environment variable is specified by https://no-color.org/.
+The environment variable @code{NO_COLOR} can be used to suppress styling
+in the textual output.  When this environment variable is set (to any value),
+@code{libtextstyle}-enabled programs will not emit colors and other text
+styling.
+
+This environment variable can be overridden by passing the command-line option
+@samp{--color=always} (see @ref{The --color option}).
+
 @node Emacs
 @section Emacs as a terminal emulator
 
diff --git a/libtextstyle/examples/color-filter/filter.c b/libtextstyle/examples/color-filter/filter.c
@@ -88,7 +88,9 @@ main (int argc, char *argv[])
   }
 
   if (color_mode == color_yes
-      || (color_mode == color_tty && isatty (STDOUT_FILENO))
+      || (color_mode == color_tty
+          && isatty (STDOUT_FILENO)
+          && getenv ("NO_COLOR") == NULL)
       || color_mode == color_html)
     {
       /* Find the style file.  */
diff --git a/libtextstyle/examples/color-hello/hello.c b/libtextstyle/examples/color-hello/hello.c
@@ -140,7 +140,9 @@ main (int argc, char *argv[])
     }
 
   if (color_mode == color_yes
-      || (color_mode == color_tty && isatty (STDOUT_FILENO))
+      || (color_mode == color_tty
+          && isatty (STDOUT_FILENO)
+          && getenv ("NO_COLOR") == NULL)
       || color_mode == color_html)
     {
       /* Find the style file.  */

Original file line number	Diff line number	Diff line change
`@@ -56,7 +56,9 @@ main (int argc, char *argv[])`
`56`	`56`	`}`
`57`	`57`
`58`	`58`	`if (color_mode == color_yes`
`59`		`- \|\| (color_mode == color_tty && isatty (STDOUT_FILENO))`
	`59`	`+ \|\| (color_mode == color_tty`
	`60`	`+ && isatty (STDOUT_FILENO)`
	`61`	`+ && getenv ("NO_COLOR") == NULL)`
`60`	`62`	`\|\| color_mode == color_html)`
`61`	`63`	`{`
`62`	`64`	`/* If no style file is explicitly specified, use the default in the`
Original file line number	Diff line number	Diff line change
`@@ -88,7 +88,9 @@ main (int argc, char *argv[])`
`88`	`88`	`}`
`89`	`89`
`90`	`90`	`if (color_mode == color_yes`
`91`		`- \|\| (color_mode == color_tty && isatty (STDOUT_FILENO))`
	`91`	`+ \|\| (color_mode == color_tty`
	`92`	`+ && isatty (STDOUT_FILENO)`
	`93`	`+ && getenv ("NO_COLOR") == NULL)`
`92`	`94`	`\|\| color_mode == color_html)`
`93`	`95`	`{`
`94`	`96`	`/* Find the style file. */`
Original file line number	Diff line number	Diff line change
`@@ -140,7 +140,9 @@ main (int argc, char *argv[])`
`140`	`140`	`}`
`141`	`141`
`142`	`142`	`if (color_mode == color_yes`
`143`		`- \|\| (color_mode == color_tty && isatty (STDOUT_FILENO))`
	`143`	`+ \|\| (color_mode == color_tty`
	`144`	`+ && isatty (STDOUT_FILENO)`
	`145`	`+ && getenv ("NO_COLOR") == NULL)`
`144`	`146`	`\|\| color_mode == color_html)`
`145`	`147`	`{`
`146`	`148`	`/* Find the style file. */`