From 1e94aa430c0eefce9396e993272309788c6a21d0 Mon Sep 17 00:00:00 2001
From: Tom Ryder <tom@sanctum.geek.nz>
Date: Tue, 23 Aug 2016 14:28:18 +1200
Subject: Fix up ?d() functions

Count arguments in right places; return 2 on usage errors where
possible; minimise subshell activity; move directory replacement
functionality to its own function `rd()` rather than overloading `cd`.
---
 sh/shrc.d/rd.sh | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)
 create mode 100644 sh/shrc.d/rd.sh

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

diff --git a/sh/shrc.d/rd.sh b/sh/shrc.d/rd.sh
new file mode 100644
index 00000000..9fd99a55
--- /dev/null
+++ b/sh/shrc.d/rd.sh
@@ -0,0 +1,63 @@
+#
+# Replace the first instance of the first argument string with the second
+# argument string in $PWD, and make that the target of the cd builtin. This is
+# to emulate a feature of the `cd` builtin in Zsh that I like, but that I think
+# should be a separate command rather than overloading `cd`.
+#
+#     $ pwd
+#     /usr/local/bin
+#     $ rd local
+#     $ pwd
+#     /usr/bin
+#     $ rd usr opt
+#     $ pwd
+#     /opt/bin
+#
+rd() {
+
+    # Check argument count
+    case $# in
+        1|2) ;;
+        *)
+            printf >&2 \
+                'rd(): Need a string and optionally a replacement\n'
+            return 2
+            ;;
+    esac
+
+    # Set the positional parameters to an option terminator and what will
+    # hopefully end up being the substituted directory name
+    set -- "$(
+
+        # 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
+        # This can be a null string or unset, in order to *remove* the pattern
+        rep=$2
+
+        # /foo/
+        curtc=${cur%%"$pat"*}
+        # /bar/ayy
+        curlc=${cur#*"$pat"}
+        # /foo/lmao/bar/ayy
+        new=${curtc}${rep}${curlc}
+
+        # Check that a substitution resulted in an actual change and that we
+        # ended up with a non-null target, or print an error to stderr
+        if [ "$cur" = "$curtc" ] || [ -z "$new" ] ; then
+            printf >&2 'rd(): Substitution failed\n'
+            exit 1
+        fi
+
+        # Print the target
+        printf '%s\n' "$new"
+    )"
+
+    # If the subshell printed nothing, return with failure
+    [ -n "$1" ] || return
+
+    # Try to change into the determined directory
+    command cd -- "$@"
+}
-- 
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