From 8028560f8260aeea6fee1206cf8704a0a5fc25f9 Mon Sep 17 00:00:00 2001
From: nicm <nicm>
Date: Sun, 31 Jan 2016 09:54:46 +0000
Subject: [PATCH] Support negative trim values (#{=-10:pane_title}) to trim
 from the end, suggested by Kevin Brubeck Unhammer.

---
 format.c | 12 ++++++++----
 tmux.1   | 10 +++++++---
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/format.c b/format.c
index efa9d1e1..78c177cd 100644
--- a/format.c
+++ b/format.c
@@ -684,7 +684,7 @@ format_replace(struct format_tree *ft, const char *key, size_t keylen,
 	char		*copy, *copy0, *endptr, *ptr, *found, *new, *value;
 	char		*from = NULL, *to = NULL;
 	size_t		 valuelen, newlen, fromlen, tolen, used;
-	u_long		 limit = 0;
+	long		 limit = 0;
 	int		 modifiers = 0, brackets;
 
 	/* Make a copy of the key. */
@@ -696,8 +696,8 @@ format_replace(struct format_tree *ft, const char *key, size_t keylen,
 	switch (copy[0]) {
 	case '=':
 		errno = 0;
-		limit = strtoul(copy + 1, &endptr, 10);
-		if (errno == ERANGE && limit == ULONG_MAX)
+		limit = strtol(copy + 1, &endptr, 10);
+		if (errno == ERANGE && (limit == LONG_MIN || limit == LONG_MAX))
 			break;
 		if (*endptr != ':')
 			break;
@@ -813,10 +813,14 @@ format_replace(struct format_tree *ft, const char *key, size_t keylen,
 	}
 
 	/* Truncate the value if needed. */
-	if (limit != 0) {
+	if (limit > 0) {
 		new = utf8_trimcstr(value, limit);
 		free(value);
 		value = new;
+	} else if (limit < 0) {
+		new = utf8_rtrimcstr(value, -limit);
+		free(value);
+		value = new;
 	}
 
 	/* Expand the buffer and copy in the value. */
diff --git a/tmux.1 b/tmux.1
index e70b07c3..5dbf6b84 100644
--- a/tmux.1
+++ b/tmux.1
@@ -3377,9 +3377,13 @@ if not.
 A limit may be placed on the length of the resultant string by prefixing it
 by an
 .Ql = ,
-a number and a colon, so
-.Ql #{=10:pane_title}
-will include at most the first 10 characters of the pane title.
+a number and a colon.
+Positive numbers count from the start of the string and negative from the end,
+so
+.Ql #{=5:pane_title}
+will include at most the first 5 characters of the pane title, or
+.Ql #{=-5:pane_title}
+the last 5 characters.
 Prefixing a time variable with
 .Ql t:
 will convert it to a string, so if