pager: remove 'S' from $LESS by default

By default, Git used to set $LESS to -FRSX if $LESS was not set by
the user. The FRX flags actually make sense for Git (F and X because
sometimes the output Git pipes to less is short, and R because Git
pipes colored output). The S flag (chop long lines), on the other
hand, is not related to Git and is a matter of user preference. Git
should not decide for the user to change LESS's default.

More specifically, the S flag harms users who review untrusted code
within a pager, since a patch looking like:

    -old code;
    +new good code; [... lots of tabs ...] malicious code;

would appear identical to:

    -old code;
    +new good code;

Users who prefer the old behavior can still set the $LESS environment
variable to -FRSX explicitly, or set core.pager to 'less -S'.

The documentation in config.txt is made a bit longer to keep both an
example setting the 'S' flag (needed to recover the old behavior)
and an example showing how to unset a flag set by Git.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index d8b6cc965..f57b0e2fc 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -558,14 +558,19 @@ core.pager::
 	configuration, then `$PAGER`, and then the default chosen at
 	compile time (usually 'less').
 +
-When the `LESS` environment variable is unset, Git sets it to `FRSX`
+When the `LESS` environment variable is unset, Git sets it to `FRX`
 (if `LESS` environment variable is set, Git does not change it at
 all).  If you want to selectively override Git's default setting
-for `LESS`, you can set `core.pager` to e.g. `less -+S`.  This will
+for `LESS`, you can set `core.pager` to e.g. `less -S`.  This will
 be passed to the shell by Git, which will translate the final
-command to `LESS=FRSX less -+S`. The environment tells the command
-to set the `S` option to chop long lines but the command line
-resets it to the default to fold long lines.
+command to `LESS=FRX less -S`. The environment does not set the
+`S` option but the command line does, instructing less to truncate
+long lines. Similarly, setting `core.pager` to `less -+F` will
+deactivate the `F` option specified by the environment from the
+command-line, deactivating the "quit if one screen" behavior of
+`less`.  One can specifically activate some flags for particular
+commands: for example, setting `pager.blame` to `less -S` enables
+line truncation only for `git blame`.
 +
 Likewise, when the `LV` environment variable is unset, Git sets it
 to `-c`.  You can override this setting by exporting `LV` with