Add --print option to get selection but not attach

README.md

@@ -37,12 +37,16 @@ Copy the `zp` script somewhere on your `PATH`.
 ## Usage
 
 ```
-usage: zp [root ...]
+usage: zp [--print] [root ...]
 
 zmx-picker - lists zmx sessions, plus repos under any roots
 given as arguments or $ZP_ROOT (colon-separated)
 
-options: -h/--help, -V/--version
+options:
+  --print        Print directory and complete session name, each NUL-terminated,
+                 instead of attaching; cancellation emits nothing
+  -h, --help     Show this help message
+  -V, --version  Print the version
 ```
 
 For example, to always pick from repositories under `~/src`, set:
@@ -89,6 +93,33 @@ Any [zmx] session labels (`zmx set <name> key=value`) are shown alongside each
 session and are fuzzy-searchable, so typing `key=value` narrows the picker to
 the sessions that carry that label.
 
+### Selecting without attaching
+
+Use `zp --print [root ...]` to select a session for another command, such as an
+autossh wrapper that reconnects to the same selection. Selecting an entry prints
+two NUL-terminated fields to stdout, with no trailing newline:
+
+1. The directory from which to attach: the repository directory when selecting a
+   repository, or the directory where `zp` was launched when selecting an
+   existing session or typing a name. This is not the selected session's
+   original starting directory or its live `cwd` reported by zmx.
+2. The complete session name, including `ZMX_SESSION_PREFIX` when set. Clear
+   that variable when attaching so zmx does not apply the prefix again.
+
+Selection does not create or attach a session. Esc or Ctrl-C cancels with exit
+status 0 and no output. The picker still supports Ctrl-X to kill sessions.
+
+In Bash, read the fields directly; command substitution (`$(zp --print)`) cannot
+preserve NUL bytes. For example, to attach to the selection:
+
+```bash
+if { IFS= read -r -d '' start_dir && IFS= read -r -d '' session_name; } < <(zp --print); then
+    (cd "$start_dir" && ZMX_SESSION_PREFIX= zmx attach "$session_name")
+fi
+```
+
+The reads fail on cancellation, so the example does not attach in that case.
+
 ## License
 
 zmx-picker is released under the [Zero Clause BSD License](LICENSE) (SPDX:

tests/harness.exp

@@ -3,9 +3,9 @@
 # blocks until a terminal answers, so every expect below responds to
 # them; without that the picker stalls and looks like zero matches.
 #
-# Usage: harness.exp <zp-path> <root-or-empty> [keys ...]
+# Usage: harness.exp <zp-path> [--print] <root-or-empty> [keys ...]
 # Each keys argument is sent after a settle period. Exits with zp's
-# exit status.
+# exit status. With --print, captures stdout in $ZP_TEST_DIR/selection.
 
 log_user 0
 
@@ -18,16 +18,25 @@ proc idle {secs} {
 }
 
 set zp [lindex $argv 0]
-set root [lindex $argv 1]
+set argv [lrange $argv 1 end]
+set print_mode [expr {[lindex $argv 0] eq "--print"}]
+if {$print_mode} {
+	set argv [lrange $argv 1 end]
+}
+set root [lindex $argv 0]
+set roots {}
+if {$root ne ""} {
+	lappend roots $root
+}
 
-if {$root eq ""} {
-	spawn -noecho $zp
+if {$print_mode} {
+	spawn -noecho sh -c {exec "$@" > "$ZP_TEST_DIR/selection"} sh $zp --print {*}$roots
 } else {
-	spawn -noecho $zp $root
+	spawn -noecho $zp {*}$roots
 }
 catch { exec stty rows 40 columns 120 < $spawn_out(slave,name) 2> /dev/null }
 
-foreach keys [lrange $argv 2 end] {
+foreach keys [lrange $argv 1 end] {
 	idle 2
 	send -- $keys
 }

tests/run.sh

@@ -214,5 +214,43 @@ else
 	not_ok '--version and -V report the version' "$out"
 fi
 
+# Compare files to preserve NUL delimiters and catch any extra stdout.
+# assert_print <description> <root> <query> <key> <directory> <session>
+# An empty expected directory means cancellation should emit no bytes.
+assert_print() {
+	local description=$1 rc=0
+	reset_log
+	rm -f "$ZP_TEST_DIR/selection"
+	: >"$ZP_TEST_DIR/expected"
+	if [[ -n $5 ]]; then
+		printf '%s\0%s\0' "$5" "$6" >"$ZP_TEST_DIR/expected"
+	fi
+	run --print "$2" "$3" "$4" || rc=$?
+	if [[ $rc -eq 0 && -z $(log) ]] &&
+		cmp -s "$ZP_TEST_DIR/expected" "$ZP_TEST_DIR/selection"; then
+		ok "$description"
+	else
+		not_ok "$description" "rc=$rc log=$(log); output bytes: $(od -An -tx1 "$ZP_TEST_DIR/selection" 2>/dev/null)"
+	fi
+}
+
+ZMX_SESSION_PREFIX='' assert_print '--print emits the caller directory and existing name without attaching' \
+	'' 'beta' "$enter" "$PWD" beta
+ZMX_SESSION_PREFIX=d. assert_print '--print never re-applies the prefix to an existing name' \
+	'' 'gamma' "$enter" "$PWD" d.gamma
+ZMX_SESSION_PREFIX='' assert_print '--print emits an unmatched query without attaching' \
+	'' 'zzz-new' "$enter" "$PWD" zzz-new
+ZMX_SESSION_PREFIX=d. assert_print '--print prefixes an unmatched query' \
+	'' 'zzz-new' "$enter" "$PWD" d.zzz-new
+ZMX_SESSION_PREFIX=d. assert_print '--print ctrl-n uses the query even with a match highlighted' \
+	'' 'bet' "$ctrl_n" "$PWD" d.bet
+
+print_root="$ZP_TEST_DIR/root with spaces"
+mkdir -p "$print_root/omega/.git"
+ZMX_SESSION_PREFIX=d. assert_print '--print preserves repo paths with spaces and numbers prefixed sessions' \
+	"$print_root" '[repo] omega' "$enter" "$print_root/omega" d.omega.10
+assert_print '--print cancellation exits successfully with no output or attach' \
+	'' '' "$esc" '' ''
+
 printf '\n%d passed, %d failed\n' "$pass" "$fail"
 [[ $fail -eq 0 ]]

zp

@@ -243,6 +243,14 @@ next_session() {
 	printf '%s.%s\n' "$base" "$next"
 }
 
+attach() {
+	if [[ $mode == print ]]; then
+		printf '%s\0%s\0' "$PWD" "${ZMX_SESSION_PREFIX:-}$1"
+	else
+		zmx attach "$1"
+	fi
+}
+
 select_session() {
 	local output rc query key selected
 	local type value
@@ -324,7 +332,7 @@ select_session() {
 			printf 'ctrl-n needs a typed query to name the new session\n' >&2
 			return 1
 		fi
-		zmx attach "$query"
+		attach "$query"
 		return 0
 	fi
 
@@ -335,13 +343,13 @@ select_session() {
 		session)
 			# The listed name is already complete; keep zmx from
 			# applying $ZMX_SESSION_PREFIX to it again.
-			ZMX_SESSION_PREFIX='' zmx attach "$value"
+			ZMX_SESSION_PREFIX='' attach "$value"
 			;;
 
 		repo)
 			(
 				cd "$value"
-				zmx attach "$(next_session "$value")"
+				attach "$(next_session "$value")"
 			)
 			;;
 
@@ -356,7 +364,7 @@ select_session() {
 	if [[ -n $query ]]; then
 		# No candidate matched, so use the entered query as a new
 		# session name in the current directory.
-		zmx attach "$query"
+		attach "$query"
 		return
 	fi
 
@@ -375,11 +383,22 @@ case ${1:-} in
 	mode='kill'
 	shift
 	;;
+--print)
+	# Print the selection as NUL-terminated start_dir and session_name
+	# instead of attaching. session_name is complete, callers should set
+	# ZMX_SESSION_PREFIX=.
+	mode='print'
+	shift
+	;;
 -h | --help)
-	printf 'usage: %s [root ...]\n\n' "${0##*/}"
+	printf 'usage: %s [--print] [root ...]\n\n' "${0##*/}"
 	printf 'zmx-picker - lists zmx sessions, plus repos under any roots\n'
 	printf 'given as arguments or $ZP_ROOT (colon-separated)\n\n'
-	printf 'options: -h/--help, -V/--version\n'
+	printf 'options:\n'
+	printf '  --print        Print directory and complete session name, each NUL-terminated,\n'
+	printf '                 instead of attaching; cancellation emits nothing\n'
+	printf '  -h, --help     Show this help message\n'
+	printf '  -V, --version  Print the version\n'
 	exit 0
 	;;
 -V | --version)