Fix psql \s to work with recent libedit, and add pager support

Enterprise / PostgreSQL - Tom Lane [sss.pgh.pa.us] - 8 September 2014 15:09 UTC

psql's \s (print command history) doesn't work at all with recent libedit
versions when printing to the terminal, because libedit tries to do an fchmod() on the target file which will fail if the target is /dev/tty. (We'd already noted this in the context of the target being /dev/null.) Even before that, it didn't work pleasantly, because libedit likes to encode the command history file (to ensure successful reloading), which renders it nigh unreadable, not to mention significantly different-looking depending on exactly which libedit version you have. So let's forget using write_history() for this purpose, and instead print the data ourselves, using logic similar to that used to iterate over the history for newline encoding/decoding purposes.

While we're at it, insert the ability to use the pager when \s is printing to the terminal. This has been an acknowledged shortcoming of \s for many years, so while you could argue it's not exactly a back-patchable bug fix it still seems like a good improvement. Anyone who's seriously annoyed at this can use "\s /dev/tty" or local equivalent to get the old behavior.

Experimentation with this showed that the history iteration logic was actually rather broken when used with libedit. It turns out that with libedit you have to use previous_history() not next_history() to advance to more recent history entries. The easiest and most robust fix for this seems to be to make a run-time test to verify which function to call. We had not noticed this because libedit doesn't really need the newline encoding logic: its own encoding ensures that command entries containing newlines are reloaded correctly (unlike libreadline). So the effective behavior with recent libedits was that only the oldest history entry got newline-encoded or newline-decoded. However, because of yet other bugs in history_set_pos(), some old versions of libedit allowed the existing loop logic to reach entries besides the oldest, which means there may be libedit ~/.psql_history files out there containing encoded newlines in more than just the oldest entry. To ensure we can reload such files, it seems appropriate to back-patch this fix, even though that will result in some incompatibility with older psql versions (ie, multiline history entries written by a psql with this fix will look corrupted to a psql without it, if its libedit is reasonably up to date).

Stepan Rutz and Tom Lane

750c5ee Fix psql \s to work with recent libedit, and add pager support.
doc/src/sgml/ref/psql-ref.sgml | 16 ++--
src/bin/psql/command.c | 14 +---
src/bin/psql/input.c | 163 ++++++++++++++++++++++++++++++++--------
src/bin/psql/input.h | 3 +-
4 files changed, 144 insertions(+), 52 deletions(-)

Upstream: git.postgresql.org

  • Share