From 2d0fefe4cde7831c7e49641df217ee0354751a63 Mon Sep 17 00:00:00 2001
From: Tom Ryder <tom@sanctum.geek.nz>
Date: Fri, 26 May 2017 20:24:13 +1200
Subject: Reimplement ud()

More fault-tolerant and no subshell or temporary vars
---
 sh/shrc.d/ud.sh | 62 ++++++++++++++++++++++++++++-----------------------------
 1 file changed, 30 insertions(+), 32 deletions(-)

(limited to 'sh')

diff --git a/sh/shrc.d/ud.sh b/sh/shrc.d/ud.sh
index 79f4b5e7..a3997702 100644
--- a/sh/shrc.d/ud.sh
+++ b/sh/shrc.d/ud.sh
@@ -2,48 +2,46 @@
 # like cd .., cd ../.., etc
 ud() {
 
-    # Check argument count
-    if [ "$#" -gt 1 ] ; then
+    # Check arguments; default to 1 and $PWD
+    if [ "$#" -gt 2 ] ; then
         printf >&2 'ud(): Too many arguments\n'
         return 2
     fi
+    set -- "${1:-1}" "${2:-"$PWD"}"
+    set -- "$1" "$2"
 
-    # Check first argument, number of steps upward, default to 1.
-    # "0" is weird, but valid; "-1" however makes no sense at all
-    if [ "${1:-1}" -lt 0 ] ; then
+    # Check first argument, number of steps upward. "0" is weird, but valid;
+    # "-1" however makes no sense at all
+    if [ "$1" -lt 0 ] ; then
         printf >&2 'ud(): Invalid step count\n'
         return 2
     fi
 
-    # Change the positional parameters from the number of steps given to a
-    # "../../.." string
-    set -- "$(
-
-        # Append /.. to the target (default PWD) the specified number of times
-        dirname=${2:-"$PWD"}
-        i=0
-        steps=${1:-1}
-        while [ "$i" -lt "$steps" ] ; do
-            dirname=${dirname%/}/..
-            i=$((i+1))
+    # Check second argument, starting path, for relativity and anchor it if
+    # need be
+    case $2 in
+        /*) ;;
+        *) set -- "$1" "$PWD"/"$2" ;;
+    esac
+
+    # Chop an element off the target the specified number of times
+    while [ "$1" -gt 0 ] ; do
+
+        # Make certain there are no trailing slashes to foul us up
+        while : ; do
+            case $2 in
+                */) set -- "$1" "${2%/}" ;;
+                *) break ;;
+            esac
         done
 
-        # Check we have a target after all that
-        if [ -z "$dirname" ] ; then
-            printf >&2 'ud(): Destination construction failed\n'
-            exit 1
-        fi
+        # Strip a path element
+        set -- "$(($1-1))" "${2%/*}"
+    done
 
-        # Print the target with trailing slash to work around newline stripping
-        printf '%s/' "${dirname%/}"
-    )"
+    # Shift off the count, which should now be zero
+    shift
 
-    # Remove trailing slash
-    set -- "${1%/}"
-
-    # If the subshell printed nothing, return with failure
-    [ -n "$1" ] || return
-
-    # Try to change into the determined directory
-    command cd -- "$@"
+    # Try to change into the determined directory, or the root if blank
+    command cd -- "${1:-/}"
 }
-- 
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