Port sd() to POSIX sh

3 files changed, 83 insertions, 110 deletions

diff --git a/README.markdown b/README.markdown
index 9bbf12d9..e9e04201 100644
--- a/README.markdown
+++ b/README.markdown
@@ -185,6 +185,7 @@ in `sh/shrc.d` to be loaded by any POSIX interactive shell. Those include:
 *   `rcsdiff()` forces a unified format for `rcsdiff(1)`.
 *   `scp()` tries to detect forgotten hostnames in `scp(1)` command calls.
 *   `scr()` creates a temporary directory and changes into it.
+*   `sd()` changes into a sibling of the current directory.
 *   `sudo()` forces `-H` for `sudo(8)` calls so that `$HOME` is never
     preserved; I hate ending up `root`-owned files in my home directory.
 *   `tmux()` changes the default command for `tmux(1)` to `attach-session -d`
@@ -211,7 +212,6 @@ There are a few other little tricks defined for other shells, mostly in
 *   `pushd()` adds a default destination of `$HOME` to the `pushd` builtin.
 *   `readv()` prints names and values from `read` calls to `stderr`.
 *   `readz()` is an alias for `read -d '' -r`.
-*   `sd()` changes into a sibling of the current directory.
 *   `vared()` allows interactively editing a variable with Readline, emulating
     a Zsh function I like by the same name.
 *   `vr()` tries to change to the root directory of a source control
diff --git a/bash/bashrc.d/sd.bash b/bash/bashrc.d/sd.bash
deleted file mode 100644
index ad4a0deb..00000000
--- a/bash/bashrc.d/sd.bash
+++ /dev/null
@@ -1,109 +0,0 @@
-#
-# sd -- sibling/switch directory -- Shortcut to switch to another directory
-# with the same parent, i.e. a sibling of the current directory.
-#
-#     $ pwd
-#     /home/you
-#     $ sd friend
-#     $ pwd
-#     /home/friend
-#     $ sd you
-#     $ pwd
-#     /home/you
-#
-# If no arguments are given and there's only one other sibling, switch to that;
-# nice way to quickly toggle between two siblings.
-#
-#     $ cd -- "$(mktemp -d)"
-#     $ pwd
-#     /tmp/tmp.ZSunna5Eup
-#     $ mkdir a b
-#     $ ls
-#     a b
-#     $ cd a
-#     pwd
-#     /tmp/tmp.ZSunna5Eup/a
-#     $ sd
-#     $ pwd
-#     /tmp/tmp.ZSunna5Eup/b
-#     $ sd
-#     $ pwd
-#     /tmp/tmp.ZSunna5Eup/a
-#
-# Seems to work for symbolic links.
-#
-sd() {
-
-    # For completeness' sake, we'll pass any options to cd
-    local arg
-    local -a opts
-    for arg ; do
-        case $arg in
-            --)
-                shift
-                break
-                ;;
-            -*)
-                shift
-                opts[${#opts[@]}]=$arg
-                ;;
-            *)
-                break
-                ;;
-        esac
-    done
-
-    # Set up local variable for the sibling to which we'll attempt to move,
-    # assuming we find one
-    local dirname
-
-    # If we have one argument, it's easy, we just try to move to that one
-    if (($# == 1)) ; then
-        dirname=$1
-
-    # If no argument, the user is lazy; if there's only one sibling, we'll do
-    # what they mean and switch to it
-    elif (($# == 0)) ; then
-
-        # This subshell switches on globbing functions to try to find all the
-        # current directory's siblings; it exits non-zero if it found anything
-        # other than one
-        if ! dirname=$(
-            shopt -s dotglob extglob nullglob
-            local -a siblings
-
-            # Generate relative paths of all siblings
-            siblings=(../!("${PWD##*/}")/)
-
-            # Strip the trailing slash
-            siblings=("${siblings[@]%/}")
-
-            # Strip everything up to the basename
-            siblings=("${siblings[@]##*/}")
-
-            # If some number of siblings besides one, exit non-zero
-            if ((${#siblings[@]} != 1)) ; then
-                exit 1
-            fi
-
-            # Otherwise, just print it
-            printf %s "${siblings[0]}"
-
-        # This block is run if the subshell fails due to there not being a
-        # single sibling
-        ) ; then
-            printf 'bash: %s: No single sibling directory\n' \
-                "$FUNCNAME" >&2
-            return 1
-        fi
-
-    # Any other number of arguments is a usage error; say so
-    else
-        printf 'bash: %s: usage: %s [DIR]\n' \
-            "$FUNCNAME" "$FUNCNAME" >&2
-        return 2
-    fi
-
-    # Try to change into the determined directory
-    builtin cd "${opts[@]}" ../"$dirname"
-}
diff --git a/sh/shrc.d/sd.sh b/sh/shrc.d/sd.sh
new file mode 100644
index 00000000..c6513aac
--- /dev/null
+++ b/sh/shrc.d/sd.sh
@@ -0,0 +1,82 @@
+#
+# sd -- sibling/switch directory -- Shortcut to switch to another directory
+# with the same parent, i.e. a sibling of the current directory.
+#
+#     $ pwd
+#     /home/you
+#     $ sd friend
+#     $ pwd
+#     /home/friend
+#     $ sd you
+#     $ pwd
+#     /home/you
+#
+# If no arguments are given and there's only one other sibling, switch to that;
+# nice way to quickly toggle between two siblings.
+#
+#     $ cd -- "$(mktemp -d)"
+#     $ pwd
+#     /tmp/tmp.ZSunna5Eup
+#     $ mkdir a b
+#     $ ls
+#     a b
+#     $ cd a
+#     pwd
+#     /tmp/tmp.ZSunna5Eup/a
+#     $ sd
+#     $ pwd
+#     /tmp/tmp.ZSunna5Eup/b
+#     $ sd
+#     $ pwd
+#     /tmp/tmp.ZSunna5Eup/a
+#
+# Seems to work for symbolic links.
+#
+sd() {
+
+    set -- "$(
+    
+        # Check argument count
+        if [ "$#" -gt 1 ] ; then
+            printf >&2 'sd(): Too many arguments\n'
+            exit 1
+        fi
+
+        # Set the positional parameters to either the requested directory, or
+        # all of the current directory's siblings if no request
+        spec=$1
+        set --
+        if [ -n "$spec" ] ; then
+            set -- "$@" ../"$spec"
+        else
+            for sib in ../.* ../* ; do
+                case ${sib#../} in
+                    .|..|"${PWD##*/}") continue ;;
+                esac
+                set -- "$@" "$sib"
+            done
+        fi
+
+        # We should have exactly one sibling
+        case $# in
+            1) ;;
+            0)
+                printf >&2 'sd(): No siblings\n'
+                exit 1
+                ;;
+            *)
+                printf >&2 'sd(): More than one sibling\n'
+                exit 1
+                ;;
+        esac
+
+        # Print the target
+        printf '%s\n' "$1"
+    )"
+
+    # If the subshell printed nothing, return with failure
+    [ -n "$1" ] || return
+
+    # Try to change into the determined directory
+    command cd -- "$@"
+}