From 6638e53935ee1c5f3bfb23c08bd2aae2994b6219 Mon Sep 17 00:00:00 2001
From: "Alex Xu (Hello71)" <alex_y_xu@yahoo.ca>
Date: Sat, 4 Apr 2020 19:52:57 -0400
Subject: change algorithm, fix edge cases, add tests

---
 nextbin    | 116 +++++++++++++++++++++++++++++++++++++++++++++++++------------
 test/a/x   |   3 ++
 test/b/x   |   3 ++
 test/c/x   |   3 ++
 test/start |  59 +++++++++++++++++++++++++++++++
 5 files changed, 162 insertions(+), 22 deletions(-)
 create mode 100755 test/a/x
 create mode 100755 test/b/x
 create mode 100755 test/c/x
 create mode 100755 test/start

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 "$exe" "$@"
diff --git a/test/a/x b/test/a/x
new file mode 100755
index 0000000..e7d6387
--- /dev/null
+++ b/test/a/x
@@ -0,0 +1,3 @@
+#!/bin/sh
+echo "in a with $0, next"
+nextbin "$0" "$@"
diff --git a/test/b/x b/test/b/x
new file mode 100755
index 0000000..0355509
--- /dev/null
+++ b/test/b/x
@@ -0,0 +1,3 @@
+#!/bin/sh
+echo "in b with $0, next"
+nextbin "$0" "$@"
diff --git a/test/c/x b/test/c/x
new file mode 100755
index 0000000..cc0070b
--- /dev/null
+++ b/test/c/x
@@ -0,0 +1,3 @@
+#!/bin/sh
+echo "in c with $0, done"
+exit 0
diff --git a/test/start b/test/start
new file mode 100755
index 0000000..4cf0d9d
--- /dev/null
+++ b/test/start
@@ -0,0 +1,59 @@
+#!/bin/sh
+
+set -e
+
+cd "${0%/*}"
+exec 2>&1
+
+check() {
+    for arg in $1; do
+        read -r line || { echo "FAIL: insufficient output" >&2; return 1; }
+        echo "GOT: $line"
+        case "$arg" in
+            [a-z]) case "$line" in "in $arg "*) ;; *) echo "FAIL: expected $arg" >&2; return 1; esac;;
+            err) case "$line" in nextbin*failed*) ;; *) echo "FAIL: expected err" >&2; return 1; esac;;
+            *) echo "INVALID TEST" >&2; exit 1
+        esac
+    done
+    if read -r line; then
+        echo "FAIL: too much output" >&2
+        return 1
+    fi
+    echo "OK"
+}
+
+try() {
+    # shellcheck disable=SC2016
+    printf 'TEST: PATH="$PATH:%s" %s, expect %s\n' "$@"
+    PATH="$PATH:$1" "$2" 2>&1 | check "$3"
+    # shellcheck disable=SC2016
+    printf 'TEST: PATH="%s:$PATH" %s, expect %s\n' "$@"
+    PATH="$1:$PATH" "$2" 2>&1 | check "$3"
+}
+
+do_try() {
+    try "$1" "$2/x" "$3"
+    try "$1" "./$2/x" "$3"
+    try "$1" "$PWD/$2/x" "$3"
+    try "$1" "$2/../$2/x" "$3"
+    try "$1" "./$2/../$2/x" "$3"
+    try "$1" "$PWD/$2/../$2/x" "$3"
+    echo
+}
+
+do_try2() {
+    try "$1" "x" "$3"
+    do_try "$@"
+}
+
+export PATH="$PWD/..:$PATH"
+
+do_try "" a "a err"
+do_try2 "$PWD/a" a "a err"
+do_try "$PWD/b" a "a b err"
+do_try2 "$PWD/a:$PWD/b" a "a b err"
+do_try "$PWD/a:$PWD/b" b "b err"
+do_try2 "$PWD/a:$PWD/b:$PWD/c" a "a b c"
+do_try "$PWD/a:$PWD/b:$PWD/c" b "b c"
+
+echo "ALL TESTS COMPLETED SUCCESSFULLY :)"
-- 
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