1 files changed, 94 insertions, 22 deletions
diff --git a/nextbin b/nextbin
index 2e1d9dd..fd8faa5 100755
--- a/nextbin
+++ b/nextbin
@@ -1,31 +1,103 @@
 #!/bin/sh
 
-orig_exe=$(realpath -s "$1")
+set -e
+
+die() {
+    fmt=$1
+    shift
+    printf "nextbin %s failed: $fmt\n" "$orig_exe" "$@" >&2
+    exit 1
+}
+
+usage() {
+    # shellcheck disable=SC2016
+    echo 'usage: nextbin [-v] "$0" "$@"' >&2
+}
+
+case "$1" in
+    -v) action="echo"; shift;;
+    -*|'') usage; exit 1;;
+    *) action="exec"
+esac
+orig_exe=$1
+shift
 exe_name=${orig_exe##*/}
+
+[ -n "$PATH" ] || die 'PATH is empty'
+
 case "$orig_exe" in
-    */*) ;;
+    */)
+        die 'ends with /'
+        ;;
+
+    */*)
+        orig_dir=${orig_exe%/*}
+        ;;
+
     *)
-        printf 'error: cannot find next executable: argv[0] is %s, missing /\n' "$orig_exe"
-        exit 1
+        # either shell has not resolved script-file into a path, or script is
+        # in cwd and PATH has . or empty entries
+        if ! [ -d "$orig_exe" ] && [ -x "$orig_exe" ]; then
+            case ":$PATH:" in
+                *::*:.:*|*:.:*::*)
+                    die 'exe in cwd and PATH has both . and empty entries'
+                    ;;
+
+                *::*)
+                    orig_dir=
+                    ;;
+
+                *:.:*)
+                    orig_dir=.
+                    ;;
+
+                *)
+                    die 'missing /'
+            esac
+        fi
 esac
-paths=
-passed_paths=
-set -f
-_IFS=$IFS
-IFS=:
-for path in $PATH; do
-    file=$path/$exe_name
-    if [ "$file" = "$orig_exe" ]; then
-        if [ -n "$passed_paths" ] && [ -n "$paths" ]; then
-            printf 'error: ambiguous next executable for %s past %s, due to multiple non-consecutive instances of %s in PATH' "$exe_name" "$orig_exe" "$(dirname "$orig_exe")"
-            exit 1
+
+tmp_path=:$PATH:
+new_path=${tmp_path#*:$orig_dir:}
+[ -n "$new_path" ] \
+    || die '%s is last PATH entry' "$orig_dir"
+if [ "$new_path" != "$tmp_path" ]; then
+    new_path_2=${new_path#*:$orig_dir:}
+    [ "$new_path" = "$new_path_2" ] \
+        || die 'duplicate entry in PATH: %s' \
+            "$orig_exe" "$orig_dir"
+else
+    # try to find equivalent path
+    found_alt_dir=
+    new_orig_dir=
+    equiv_orig_dir=$(cd "${orig_dir:-.}" && pwd -L)
+    tmp_path_2=$PATH
+    while :; do
+        p=${tmp_path_2%%:*}
+        if [ "$(cd "$p" >/dev/null 2>&1 && pwd -L)" = "$equiv_orig_dir" ]; then
+            [ -z "$found_alt_dir" ] \
+                || die "duplicate equivalent path in PATH: '%s' = '%s'" \
+                    "$new_orig_dir" "$p"
+            found_alt_dir=1
+            new_orig_dir=$p
         fi
-        passed_paths=${paths+$paths:}
-        paths=
+        case "$tmp_path_2" in
+            *:*) tmp_path_2=${tmp_path_2#*:};;
+            *) break
+        esac
+    done
+    if [ -n "$found_alt_dir" ]; then
+        new_path=${tmp_path#*:$new_orig_dir:}
+        [ -n "$new_path" ] \
+            || die '%s is last PATH entry' "$new_orig_dir"
     else
-        paths="${paths+$paths:}$path"
+        new_path=$PATH:
     fi
-done
-IFS=$_IFS
-PATH="$passed_paths$paths" exec "$exe_name"
-exit 1
+fi
+
+exe=$(PATH="${new_path%:}" command -v "$exe_name") || true
+[ -n "$exe" ] \
+    || die 'PATH lookup failed using %s' \
+        "${new_path%:}"
+
+$action "$exe" "$@"