From 3d8cf05dfc685e799aa5e20319e8e33288e74e04 Mon Sep 17 00:00:00 2001
From: Tom Ryder <tom@sanctum.geek.nz>
Date: Fri, 19 Aug 2016 12:48:35 +1200
Subject: Change cd() into POSIX shell script

---
 sh/shrc.d/cd.sh | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 sh/shrc.d/cd.sh

(limited to 'sh/shrc.d/cd.sh')

diff --git a/sh/shrc.d/cd.sh b/sh/shrc.d/cd.sh
new file mode 100644
index 00000000..dd98a422
--- /dev/null
+++ b/sh/shrc.d/cd.sh
@@ -0,0 +1,72 @@
+# If given two arguments, replace the first instance of the first argument with
+# the second argument in $PWD, and make that the target of cd(). This POSIX
+# version cannot handle options, but it can handle an option terminator (--),
+# so e.g. `cd -- -foo -bar` should work.
+cd() {
+
+    # First check to see if we can perform the substitution at all
+    if (
+
+        # If we have any options, we can't do it, because POSIX shell doesn't
+        # let us (cleanly) save the list of options for use later in the script
+        for arg ; do
+            case $arg in
+                --) break ;;
+                -*) return 1 ;;
+            esac
+        done
+
+        # Shift off -- if it's the first argument
+        [ "$1" = -- ] && shift
+
+        # Check we have two non-null arguments
+        [ "$#" -eq 2 ] || return
+        [ -n "$1" ] || return
+        [ -n "$2" ] || return
+
+    ) ; then
+
+        # Set the positional parameters to an option terminator and what will
+        # hopefully end up being the substituted directory name
+        set -- -- "$(
+
+            # If the first of the existing positional arguments is --, shift it
+            # off
+            [ "$1" = -- ] && shift
+
+            # Current path: e.g. /foo/ayy/bar/ayy
+            cur=$PWD
+            # Pattern to replace: e.g. ayy
+            pat=$1
+            # Text with which to replace pattern: e.g. lmao
+            rep=$2
+
+            # /foo/
+            curtc=${cur%%"$pat"*}
+            # /bar/ayy
+            curlc=${cur#*"$pat"}
+            # /foo/lmao/bar/ayy
+            new=${curtc}${rep}${curlc}
+
+            # Check pattern was actually in $PWD; this indirectly checks that
+            # $PWD and $pat are both actually set, too; it's valid for $rep to
+            # be empty, though
+            [ "$cur" != "$curtc" ] || exit
+
+            # Check we ended up with something to change into
+            [ -n "$new" ] || exit
+
+            # Print the replaced result
+            printf '%s\n' "$new"
+        )"
+
+        # Check we have a second argument
+        if [ -z "$2" ] ; then
+            printf >&2 'cd(): Substitution failed\n'
+            return 1
+        fi
+    fi
+
+    # Execute the cd command as normal
+    command cd "$@"
+}
-- 
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