Add option --date=FORMAT to specify the date part in the snapshot name.

src/zfs-auto-snapshot.8

@@ -16,6 +16,9 @@ for those in which the user-property \fBcom.sun:auto-snapshot\fR is
 set to \fBfalse\fR.  This option reverses the behavior and requires
 \fBcom.sun:auto-snapshot\fR to be set to \fBtrue\fR.
 .TP
+\fB\-D\fR, \fB\-\-date=\fIFORMAT\fR
+Use \fIformat\fR for snapshot name. See \fBdate\fR(1) for more information.
+.TP
 \fB\-d\fR, \fB\-\-debug\fR
 Print debugging messages.
 .TP

src/zfs-auto-snapshot.sh

@@ -24,6 +24,7 @@ IFS="
 "
 
 # Set default program options.
+opt_date_format='%F-%H%M'
 opt_backup_full=''
 opt_backup_incremental=''
 opt_default_exclude=''
@@ -56,6 +57,7 @@ print_usage ()
 {
 	echo "Usage: $0 [options] [-l label] <'//' | name [name...]>
   --default-exclude  Exclude datasets if com.sun:auto-snapshot is unset.
+  -D, --date=FORMAT  Date format. Default '%F-%H%M'.
   -d, --debug        Print debugging messages.
   -e, --event=EVENT  Set the com.sun:auto-snapshot-desc property to EVENT.
       --fast         Use a faster zfs list invocation.
@@ -144,6 +146,45 @@ do_run () # [argv]
 }
 
 
+setup_snap_glob ()
+{
+	local base="$1"
+	local format="$2"
+
+	# The dash to mimic the separator between prefix/label
+	# and DATE in SNAPNAME.
+	echo -n "$base"-
+	echo $format | \
+		awk -v ORS="" '{ gsub(/./,"&\n") ; print }' | \
+		while read char; do
+			[ "$char" = "%" ] && continue
+
+			if [ "$char" = "." ]; then
+				echo -n "."
+			elif [ "$char" = "-" ]; then
+				echo -n "-"
+			else
+				# Given the format char, create
+				# a string with only that.
+				# So if we said '%Y', the percentage
+				# sign would have been filtered out
+				# at the top of the loop, leaving the
+				# 'Y' here. So str=2014.
+				str=$(date +"%$char")
+
+				# Print the lenght of that with
+				# question marks (4 with the '%Y'
+				# example above).
+				i=0
+				while [ $i -lt ${#str} ]; do
+					echo -n "?"
+					i=$((i + 1))
+				done
+			fi
+		done
+}
+
+
 do_snapshots () # properties, flags, snapname, oldglob, [targets...]
 {
 	local PROPS="$1"
@@ -210,9 +251,9 @@ do_snapshots () # properties, flags, snapname, oldglob, [targets...]
 GETOPT=$(getopt \
   --longoptions=default-exclude,dry-run,fast,skip-scrub,recursive \
   --longoptions=event:,keep:,label:,prefix:,sep: \
-  --longoptions=debug,help,quiet,syslog,verbose \
+  --longoptions=date:,debug,help,quiet,syslog,verbose \
   --longoptions=pre-snapshot:,post-snapshot:,destroy-only \
-  --options=dnshe:l:k:p:rs:qgv \
+  --options=D:dnshe:l:k:p:rs:qgv \
   -- "$@" ) \
   || exit 128
 
@@ -221,6 +262,10 @@ eval set -- "$GETOPT"
 while [ "$#" -gt '0' ]
 do
 	case "$1" in
+		(-D|--date)
+			opt_date_format="$2"
+			shift 2
+			;;
 		(-d|--debug)
 			opt_debug='1'
 			opt_quiet=''
@@ -530,13 +575,13 @@ SNAPPROP="-o com.sun:auto-snapshot-desc='$opt_event'"
 
 # ISO style date; fifteen characters: YYYY-MM-DD-HHMM
 # On Solaris %H%M expands to 12h34.
-DATE=$(date --utc +%F-%H%M)
+DATE=$(date --utc +"$opt_date_format")
 
 # The snapshot name after the @ symbol.
 SNAPNAME="$opt_prefix${opt_label:+$opt_sep$opt_label}-$DATE"
 
-# The expression for matching old snapshots.  -YYYY-MM-DD-HHMM
-SNAPGLOB="$opt_prefix${opt_label:+?$opt_label}????????????????"
+# The expression for matching old snapshots.
+SNAPGLOB="$(setup_snap_glob $opt_prefix${opt_label:+?$opt_label} $opt_date_format)"
 
 if [ -n "$opt_do_snapshots" ]
 then