diff --git a/dotfiles/lib/python/shell_path.py b/dotfiles/lib/python/shell_path.py
new file mode 100755
index 00000000..ac373fdb
--- /dev/null
+++ b/dotfiles/lib/python/shell_path.py
@@ -0,0 +1,117 @@
+#!/usr/bin/env python
+import argparse
+import os
+
+
+class PathList(object):
+
+    @classmethod
+    def from_string(cls, path_string, separator=':'):
+        non_empty_paths = [path for path in path_string.split(separator) if path]
+        return cls(non_empty_paths, separator=':')
+
+    def __init__(self, paths, separator=':'):
+        self.paths = paths
+        self.separator = separator
+
+    def __str__(self):
+        return self.with_separator(self.separator)
+
+    def with_separator(self, separator=None):
+        separator = separator or self.separator
+        deduped = []
+        included = set()
+        for path in self.paths:
+            normalized = os.path.normpath(path)
+            if normalized not in included:
+                included.add(normalized)
+                deduped.append(path)
+        return separator.join(
+            os.path.normpath(path) for path in deduped
+        )
+
+    def add(self, new_paths, after=False, target=None):
+        if target:
+            target_index = self.paths.index(target)
+        else:
+            target_index = 0
+
+        if after:
+            increment = 1 if target else len(self.paths)
+            target_index += increment
+
+        self.paths = self.paths[:target_index] + new_paths + self.paths[target_index:]
+
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser(description='Manipulate path variables.')
+    parser.add_argument(
+        'paths',
+        metavar='PATH',
+        type=str,
+        nargs='*',
+        help='paths to add',
+    )
+    parser.add_argument(
+        '--path-var',
+        help='the path var to add to.',
+        default='PATH',
+    )
+    parser.add_argument(
+        '--separator',
+        help='the separator of the path variable',
+        default=':',
+    )
+    parser.add_argument(
+        '--path-string',
+        help='the path string to edit',
+        default=None,
+    )
+    parser.add_argument(
+        '--after',
+        help=('whether to do the action after the target (if target is specified)'
+              'or the entire path variable'),
+        action='store_true',
+        default=True,
+    )
+    parser.add_argument(
+        '--before',
+        help='inverse of after',
+        dest='after',
+        action='store_false',
+    )
+    parser.add_argument(
+        '--target',
+        help='the target path',
+        default=None
+    )
+    parser.add_argument(
+        '--include-assignment',
+        action='store_true',
+        help='include the assignment command in output',
+    )
+    parser.add_argument(
+        '--print-separator',
+        help='separator to use for output',
+        default=None,
+    )
+    parser.add_argument(
+        '--path-lines',
+        help='use newlines to separate path output',
+        action='store_true',
+        default=False,
+    )
+    args = parser.parse_args()
+
+    path_string = args.path_string or os.environ.get(args.path_var, '')
+    path_list = PathList.from_string(path_string, separator=args.separator)
+    path_list.add(args.paths, after=args.after, target=args.target)
+
+    output_separator = '\n' if args.path_lines else args.print_separator
+    output_path = path_list.with_separator(separator=output_separator)
+    if args.include_assignment:
+        output = "export {}='{}'".format(args.path_var, output_path)
+    else:
+        output = output_path
+
+    print(output)
diff --git a/dotfiles/lib/shellenv.sh b/dotfiles/lib/shellenv.sh
index d6117805..4eceb45c 100644
--- a/dotfiles/lib/shellenv.sh
+++ b/dotfiles/lib/shellenv.sh
@@ -7,26 +7,31 @@ function _source_shellenv_files {
     done
 }
 
+function add_to_path {
+    local result=$($HOME/.lib/python/shell_path.py --include-assignment "$@")
+    eval "$result"
+}
+
 function _setup_env {
     _path_helper
-    idem_add_to_back_of_path "$HOME/.local/lib/python2.6/site-packages"
-    idem_add_to_back_of_path "$HOME/.rvm/bin"
-    idem_add_to_front_of_path "$HOME/bin"
-    hash brew 2>/dev/null && idem_add_to_front_of_path "$(brew --prefix coreutils)/libexec/gnubin"
-    idem_add_to_front_of_path "/usr/local/bin"
+    add_to_path "$HOME/.local/lib/python2.6/site-packages" --after
+    add_to_path "$HOME/.rvm/bin" --after
+    add_to_path "$HOME/bin"
+    hash brew 2>/dev/null && add_to_path "$(brew --prefix coreutils)/libexec/gnubin"
+    add_to_path "/usr/local/bin"
 
-    idem_add_to_back_of_path `python -c 'import sysconfig; print sysconfig.get_path("scripts")'`
+    add_to_path $(python -c 'import sysconfig; print sysconfig.get_path("scripts")') --before
 
     if is_osx; then
         export CFLAGS=-Qunused-arguments
         export CPPFLAGS=-Qunused-arguments
-        idem_add_to_back_of_path "/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources"
+        add_to_path "/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources" --after
         local JDK_LOCATION="$(find /Library/Java/JavaVirtualMachines -depth 1 | head -n 1)"
         export JAVA_HOME="$JDK_LOCATION/Contents/Home"
         export STUDIO_JDK=$JDK_LOCATION
         export GRADLE_HOME="$(brew --prefix gradle)"
         export ANDROID_HOME="$(brew --prefix android-sdk)"
-        idem_add_to_back_of_path "$ANDROID_HOME"
+        add_to_path "$ANDROID_HOME" --after
         
         # Access gnu man pages.
         hash brew 2> /dev/null && export MANPATH="$(brew --prefix)/opt/coreutils/libexec/gnuman:$MANPATH"
@@ -35,10 +40,10 @@ function _setup_env {
         is_osx && export VISUAL="which emacsclient -c -n"
     fi
 
-    idem_add_to_front_of_path "$JAVA_HOME/bin"
+    add_to_path "$JAVA_HOME/bin"
 
-    idem_add_to_back_of_path "$HOME/.lib/python"
-    idem_add_to_back_of_path "/usr/local/sbin"
+    add_to_path "$HOME/.lib/python" --after
+    add_to_path "/usr/local/sbin" --after
 
     # Load RVM into a shell session *as a function*
     [[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm"
@@ -54,18 +59,18 @@ function _setup_env {
     [ -s "$NVM_DIR/nvm.sh" ] && . "$NVM_DIR/nvm.sh"  # This loads nvm
     export NODE_PATH="/usr/local/lib/node_modules/"
 
-    idem_add_to_front_of_path "$HOME/.local/bin"
-    idem_add_to_front_of_path "$HOME/.lib/python" 'PYTHONPATH'
+    add_to_path "$HOME/.local/bin"
+    add_to_path "$HOME/.lib/python" --path-var 'PYTHONPATH'
 
-    idem_add_to_front_of_path "$HOME/go" 'GOPATH'
-    idem_add_to_front_of_path "${GOPATH//://bin:}/bin"
+    add_to_path "$HOME/go" --path-var 'GOPATH'
+    add_to_path "${GOPATH//://bin:}/bin"
 
     export RBENV_ROOT=/usr/local/var/rbenv
-    idem_add_to_front_of_path "$HOME/.rbenv/bin"
+    add_to_path "$HOME/.rbenv/bin"
     hash rbenv 2> /dev/null && eval "$(rbenv init -)"
-    hash brew 2>/dev/null && idem_add_to_front_of_path "$(brew --prefix coreutils)/libexec/gnubin"
+    hash brew 2>/dev/null && add_to_path "$(brew --prefix coreutils)/libexec/gnubin"
 
-    idem_add_to_front_of_path "$HOME/.lib/bin"
+    add_to_path "$HOME/.lib/bin"
     export ENVIRONMENT_SETUP_DONE="$(date)"
 }
 
diff --git a/dotfiles/lib/shellenv/functions.sh b/dotfiles/lib/shellenv/functions.sh
index bbaa8a37..a9c1a392 100644
--- a/dotfiles/lib/shellenv/functions.sh
+++ b/dotfiles/lib/shellenv/functions.sh
@@ -1,46 +1,5 @@
 function path_lines {
-	target=${1-PATH}
-	if is_zsh; then
-		echo ${(P)target} | tr ':' '\n'
-	else 
-		echo ${!target} | tr ':' '\n'
-	fi
-}
-
-function _add_to_front_of_path_lines {
-	target=${2-PATH}
-	echo $1
-	path_lines $target | grep -Ev "^$1$"
-}
-
-function _add_to_back_of_path_lines {
-	target=${2-PATH}
-	path_lines $target | grep -Ev "^$1$"
-	echo $1
-}
-
-function remove_trailing_colon {
-	sed 's|:*$||'
-}
-
-function add_to_front_of_path {
-	target=${2-PATH}
-	export $target="$(_add_to_front_of_path_lines $1 $target | tr '\n' ':' | remove_trailing_colon)"
-}
-
-function add_to_back_of_path {
-	target=${2-PATH}
-	export $target="$(_add_to_back_of_path_lines $1 $target | tr '\n' ':' | remove_trailing_colon)"
-}
-
-function idem_add_to_front_of_path {
-    target=${2-PATH}
-    exists_in_path_var $1 $target || add_to_front_of_path $1 $target
-}
-
-function idem_add_to_back_of_path {
-    target=${2-PATH}
-    exists_in_path_var $1 $target || add_to_back_of_path $1 $target
+	shell_path.py --path-lines "$@"
 }
 
 function indirect_expand {