diff --git a/README.md b/README.md
index 9f2390a..91911af 100644
--- a/README.md
+++ b/README.md
@@ -403,13 +403,19 @@ when xinitrc is installed.
 
 ## Use transformations
 
-Transformations are used to transform a dotfile before it is
-installed. These are executed before the dotfile is installed to transform the source.
+There are two types of transformations available:
 
-Transformation commands have two arguments:
+* **read transformations** ([Config](#config) key *trans*): used to transform dotfiles before they are installed
+  (used for commands `install` and `compare`). They have two arguments:
 
-* **{0}** will be replaced with the dotfile to process
-* **{1}** will be replaced with a temporary file to store the result of the transformation
+  * **{0}** will be replaced with the dotfile to process
+  * **{1}** will be replaced with a temporary file to store the result of the transformation
+
+* **write transformations** ([Config](#config) key *trans_write**): used to transform files before updating a dotfile
+  (used for command `update`). They have two arguments
+
+  * **{0}** will be replaced with the file path to update the dotfile with
+  * **{1}** will be replaced with a temporary file to store the result of the transformation
 
 A typical use-case for transformations is when the dotfile needs to be
 stored encrypted.
@@ -420,42 +426,19 @@ dotfiles:
   f_secret:
     dst: ~/.secret
     src: secret
-    trans:
-      - gpg
+    trans: gpg
 trans:
   gpg: gpg2 -q --for-your-eyes-only --no-tty -d {0} > {1}
 ```
 
-The above config allows to store the dotfile `~/.secret` encrypted in the *dotfiles*
+The above config allows to store the dotfile `~/.secret` encrypted in the *dotpath*
 directory and uses gpg to decrypt it when `install` is run.
 
-Here's how to deploy the above solution:
-
-* import the clear dotfile (what creates the correct entries in the config file)
-
-```bash
-$ dotdrop import ~/.secret
-```
-
-* encrypt the original dotfile
-
-```bash
-$ <some-gpg-command> ~/.secret
-```
-
-* overwrite the dotfile with the encrypted version
-
-```bash
-$ cp <encrypted-version-of-secret> dotfiles/secret
-```
-
-* edit the config file and add the transformation to the dotfile
-  (as shown in the example above)
-
-* commit and push the changes
+See the wiki page for a walkthrough on how to deploy this solution as well
+as more information on transformations:
+[wiki transformation page](https://github.com/deadc0de6/dotdrop/wiki/transformations).
 
 Note that transformations cannot be used if the dotfiles is to be linked (`link: true`).
-Also `compare` won't work on dotfiles using transformations.
 
 ## Update dotdrop
 
@@ -482,17 +465,17 @@ $ sudo pip3 install dotdrop --upgrade
 Dotfiles managed by dotdrop can be updated using the `update` command. When updating, only
 dotfiles that have differences with the stored version are updated.
 A confirmation is requested from the user before any overwrite/update unless the
-`--force` switch is used.
+`-f --force` switch is used.
 
 Either provide the path of the file containing the new version of the dotfile or
-provide the dotfile key to update (as found in the config file) along with the `--key` switch.
-When using the `--key` switch and no key is provided, all dotfiles for that profile are updated.
+provide the dotfile key to update (as found in the config file) along with the `-k --key` switch.
+When using the `-k --key` switch and no key is provided, all dotfiles for that profile are updated.
 ```bash
 # update by path
 $ dotdrop update ~/.vimrc
 
-# update by key
-$ dotdrop update f_vimrc
+# update by key with the --key switch
+$ dotdrop update --key f_vimrc
 ```
 
 There are two cases when updating a dotfile:
@@ -585,7 +568,8 @@ the following entries:
   * `link`: if true dotdrop will create a symlink instead of copying (default *false*).
   * `cmpignore`: list of pattern to ignore when comparing (enclose in quotes when using wildcards).
   * `actions`: list of action keys that need to be defined in the **actions** entry below.
-  * `trans`: list of transformation keys that need to be defined in the **trans** entry below.
+  * `trans`: transformation key to apply when installing this dotfile (must be defined in the **trans** entry below).
+  * `trans_write`: transformation key to apply when updating this dotfile (must be defined in the **trans_write** entry below).
   * `ignoreempty`: if true empty template will not be deployed (defaults to the value of `ignoreempty` above)
 
 ```yaml
@@ -599,8 +583,8 @@ the following entries:
       - "<ignore-pattern>"
     actions:
       - <action-key>
-    trans:
-      - <transformation-key>
+    trans: <transformation-key>
+    trans_write: <transformation-key>
 ```
 
 * **profiles** entry: a list of profiles with the different dotfiles that
@@ -632,6 +616,12 @@ the following entries:
    <trans-key>: <command-to-execute>
 ```
 
+* **trans_write** entry (optional): a list of write transformations (see [Use transformations](#use-transformations))
+
+```
+   <trans-key>: <command-to-execute>
+```
+
 * **variables** entry (optional): a list of template variables (see [Variables](#variables))
 
 ```
diff --git a/dotdrop/action.py b/dotdrop/action.py
index 391152e..414b420 100644
--- a/dotdrop/action.py
+++ b/dotdrop/action.py
@@ -60,15 +60,15 @@ class Transform(Cmd):
         """execute transformation with {0} and {1}
         where {0} is the file to transform and
         {1} is the result file"""
-        if os.path.exists(arg1):
-            msg = 'transformation destination exists: {}'
-            self.log.warn(msg.format(arg1))
-            return False
         ret = 1
         cmd = self.action.format(arg0, arg1)
+        if os.path.exists(arg1):
+            msg = 'transformation \"{}\": destination exists: {}'
+            self.log.warn(msg.format(cmd, arg1))
+            return False
         self.log.sub('transforming with \"{}\"'.format(cmd))
         try:
             ret = subprocess.call(cmd, shell=True)
         except KeyboardInterrupt:
-            self.log.warn('action interrupted')
+            self.log.warn('transformation interrupted')
         return ret == 0
diff --git a/dotdrop/config.py b/dotdrop/config.py
index ca56bc3..b039cc8 100644
--- a/dotdrop/config.py
+++ b/dotdrop/config.py
@@ -42,7 +42,8 @@ class Cfg:
     key_actions_post = 'post'
 
     # transformations keys
-    key_trans = 'trans'
+    key_trans_r = 'trans'
+    key_trans_w = 'trans_write'
 
     # template variables
     key_variables = 'variables'
@@ -57,7 +58,8 @@ class Cfg:
     key_dotfiles_noempty = 'ignoreempty'
     key_dotfiles_cmpignore = 'cmpignore'
     key_dotfiles_actions = 'actions'
-    key_dotfiles_trans = 'trans'
+    key_dotfiles_trans_r = 'trans'
+    key_dotfiles_trans_w = 'trans_write'
 
     # profiles keys
     key_profiles = 'profiles'
@@ -101,9 +103,13 @@ class Cfg:
         # NOT linked inside the yaml dict (self.content)
         self.actions = {}
 
-        # dict of all transformation objects by trans key
+        # dict of all read transformation objects by trans key
         # NOT linked inside the yaml dict (self.content)
-        self.trans = {}
+        self.trans_r = {}
+
+        # dict of all write transformation objects by trans key
+        # NOT linked inside the yaml dict (self.content)
+        self.trans_w = {}
 
         # represents all dotfiles per profile by profile key
         # NOT linked inside the yaml dict (self.content)
@@ -174,11 +180,17 @@ class Cfg:
                             self.actions[self.key_actions_post] = {}
                         self.actions[self.key_actions_post][k] = Action(k, v)
 
-        # parse all transformations
-        if self.key_trans in self.content:
-            if self.content[self.key_trans] is not None:
-                for k, v in self.content[self.key_trans].items():
-                    self.trans[k] = Transform(k, v)
+        # parse read transformations
+        if self.key_trans_r in self.content:
+            if self.content[self.key_trans_r] is not None:
+                for k, v in self.content[self.key_trans_r].items():
+                    self.trans_r[k] = Transform(k, v)
+
+        # parse write transformations
+        if self.key_trans_w in self.content:
+            if self.content[self.key_trans_w] is not None:
+                for k, v in self.content[self.key_trans_w].items():
+                    self.trans_w[k] = Transform(k, v)
 
         # parse the profiles
         self.lnk_profiles = self.content[self.key_profiles]
@@ -213,20 +225,60 @@ class Cfg:
             itsactions = v[self.key_dotfiles_actions] if \
                 self.key_dotfiles_actions in v else []
             actions = self._parse_actions(itsactions)
-            itstrans = v[self.key_dotfiles_trans] if \
-                self.key_dotfiles_trans in v else []
-            trans = self._parse_trans(itstrans)
-            if len(trans) > 0 and link:
+
+            # parse read transformation
+            itstrans_r = v[self.key_dotfiles_trans_r] if \
+                self.key_dotfiles_trans_r in v else None
+            trans_r = None
+            if itstrans_r:
+                if type(itstrans_r) is list:
+                    msg = 'One transformation allowed per dotfile'
+                    msg += ', error on dotfile \"{}\"'
+                    self.log.err(msg.format(k))
+                    msg = 'Please modify your config file to: \"trans: {}\"'
+                    self.log.err(msg.format(itstrans_r[0]))
+                    return False
+                trans_r = self._parse_trans(itstrans_r, read=True)
+                if not trans_r:
+                    msg = 'unknown trans \"{}\" for \"{}\"'
+                    self.log.err(msg.format(itstrans_r, k))
+                    return False
+
+            # parse write transformation
+            itstrans_w = v[self.key_dotfiles_trans_w] if \
+                self.key_dotfiles_trans_w in v else None
+            trans_w = None
+            if itstrans_w:
+                if type(itstrans_w) is list:
+                    msg = 'One write transformation allowed per dotfile'
+                    msg += ', error on dotfile \"{}\"'
+                    self.log.err(msg.format(k))
+                    msg = 'Please modify your config file: \"trans_write: {}\"'
+                    self.log.err(msg.format(itstrans_w[0]))
+                    return False
+                trans_w = self._parse_trans(itstrans_w, read=False)
+                if not trans_w:
+                    msg = 'unknown trans_write \"{}\" for \"{}\"'
+                    self.log.err(msg.format(itstrans_w, k))
+                    return False
+
+            # disable transformation when link is true
+            if link and (trans_r or trans_w):
                 msg = 'transformations disabled for \"{}\"'.format(dst)
                 msg += ' because link is True'
                 self.log.warn(msg)
-                trans = []
+                trans_r = None
+                trans_w = None
+
+            # parse ignore pattern
             ignores = v[self.key_dotfiles_cmpignore] if \
                 self.key_dotfiles_cmpignore in v else []
+
+            # create new dotfile
             self.dotfiles[k] = Dotfile(k, dst, src,
                                        link=link, actions=actions,
-                                       trans=trans, cmpignore=ignores,
-                                       noempty=noempty)
+                                       trans_r=trans_r, trans_w=trans_w,
+                                       cmpignore=ignores, noempty=noempty)
 
         # assign dotfiles to each profile
         for k, v in self.lnk_profiles.items():
@@ -315,16 +367,14 @@ class Cfg:
             res[key].append(action)
         return res
 
-    def _parse_trans(self, entries):
-        """parse transformations specified for an element
-        where entries are the ones defined for this dotfile"""
-        res = []
-        for entry in entries:
-            if entry not in self.trans.keys():
-                self.log.warn('unknown trans \"{}\"'.format(entry))
-                continue
-            res.append(self.trans[entry])
-        return res
+    def _parse_trans(self, trans, read=True):
+        """parse transformation key specified for a dotfile"""
+        transformations = self.trans_r
+        if not read:
+            transformations = self.trans_w
+        if trans not in transformations.keys():
+            return None
+        return transformations[trans]
 
     def _complete_settings(self):
         """set settings defaults if not present"""
diff --git a/dotdrop/dotdrop.py b/dotdrop/dotdrop.py
index b7ff39f..13b1cac 100644
--- a/dotdrop/dotdrop.py
+++ b/dotdrop/dotdrop.py
@@ -113,7 +113,7 @@ def cmd_install(opts, conf, temporary=False, keys=[]):
         else:
             src = dotfile.src
             tmp = None
-            if dotfile.trans:
+            if dotfile.trans_r:
                 tmp = apply_trans(opts, dotfile)
                 if not tmp:
                     continue
@@ -173,7 +173,7 @@ def cmd_compare(opts, conf, tmp, focus=[], ignore=[]):
             LOG.emph('\"{}\" does not exist on local\n'.format(dotfile.dst))
 
         tmpsrc = None
-        if dotfile.trans:
+        if dotfile.trans_r:
             # apply transformation
             tmpsrc = apply_trans(opts, dotfile)
             if not tmpsrc:
@@ -387,22 +387,18 @@ def _select(selections, dotfiles):
 
 
 def apply_trans(opts, dotfile):
-    """apply the transformation to the dotfile
+    """apply the read transformation to the dotfile
     return None if fails and new source if succeed"""
     src = dotfile.src
     new_src = '{}.{}'.format(src, TRANS_SUFFIX)
-    err = False
-    for trans in dotfile.trans:
-        if opts['debug']:
-            LOG.dbg('executing transformation {}'.format(trans))
-        s = os.path.join(opts['dotpath'], src)
-        temp = os.path.join(opts['dotpath'], new_src)
-        if not trans.transform(s, temp):
-            msg = 'transformation \"{}\" failed for {}'
-            LOG.err(msg.format(trans.key, dotfile.key))
-            err = True
-            break
-    if err:
+    trans = dotfile.trans_r
+    if opts['debug']:
+        LOG.dbg('executing transformation {}'.format(trans))
+    s = os.path.join(opts['dotpath'], src)
+    temp = os.path.join(opts['dotpath'], new_src)
+    if not trans.transform(s, temp):
+        msg = 'transformation \"{}\" failed for {}'
+        LOG.err(msg.format(trans.key, dotfile.key))
         if new_src and os.path.exists(new_src):
             remove(new_src)
         return None
@@ -422,7 +418,7 @@ def main():
     try:
         conf = Cfg(os.path.expanduser(args['--cfg']))
     except ValueError as e:
-        LOG.err('error: {}'.format(str(e)))
+        LOG.err('Config format error: {}'.format(str(e)))
         return False
 
     opts = conf.get_settings()
diff --git a/dotdrop/dotfile.py b/dotdrop/dotfile.py
index b45dc56..45e14ee 100644
--- a/dotdrop/dotfile.py
+++ b/dotdrop/dotfile.py
@@ -9,9 +9,8 @@ represents a dotfile in dotdrop
 class Dotfile:
 
     def __init__(self, key, dst, src,
-                 actions={}, trans=[],
-                 link=False, cmpignore=[],
-                 noempty=False):
+                 actions={}, trans_r=None, trans_w=None,
+                 link=False, cmpignore=[], noempty=False):
         # key of dotfile in the config
         self.key = key
         # path where to install this dotfile
@@ -22,8 +21,10 @@ class Dotfile:
         self.link = link
         # list of actions
         self.actions = actions
-        # list of transformations
-        self.trans = trans
+        # read transformation
+        self.trans_r = trans_r
+        # write transformation
+        self.trans_w = trans_w
         # pattern to ignore when comparing
         self.cmpignore = cmpignore
         # do not deploy empty file
diff --git a/dotdrop/updater.py b/dotdrop/updater.py
index b63e507..448695a 100644
--- a/dotdrop/updater.py
+++ b/dotdrop/updater.py
@@ -56,12 +56,39 @@ class Updater:
 
     def _update(self, path, dotfile):
         """update dotfile from file pointed by path"""
+        ret = False
+        new_path = None
         left = os.path.expanduser(path)
         right = os.path.join(self.conf.abs_dotpath(self.dotpath), dotfile.src)
         right = os.path.expanduser(right)
-        if os.path.isdir(path):
-            return self._handle_dir(left, right)
-        return self._handle_file(left, right)
+        if dotfile.trans_w:
+            # apply write transformation if any
+            new_path = self._apply_trans_w(path, dotfile)
+            if not new_path:
+                return False
+            left = new_path
+        if os.path.isdir(left):
+            ret = self._handle_dir(left, right)
+        else:
+            ret = self._handle_file(left, right)
+        # clean temporary files
+        if new_path and os.path.exists(new_path):
+            utils.remove(new_path)
+        return ret
+
+    def _apply_trans_w(self, path, dotfile):
+        """apply write transformation to dotfile"""
+        trans = dotfile.trans_w
+        if self.debug:
+            self.log.dbg('executing write transformation {}'.format(trans))
+        tmp = utils.get_unique_tmp_name()
+        if not trans.transform(path, tmp):
+            msg = 'transformation \"{}\" failed for {}'
+            self.log.err(msg.format(trans.key, dotfile.key))
+            if os.path.exists(tmp):
+                utils.remove(tmp)
+            return None
+        return tmp
 
     def _normalize(self, path):
         """normalize the path to match dotfile"""
diff --git a/dotdrop/utils.py b/dotdrop/utils.py
index 6e1c606..b949a75 100644
--- a/dotdrop/utils.py
+++ b/dotdrop/utils.py
@@ -8,6 +8,7 @@ utilities
 import subprocess
 import tempfile
 import os
+import uuid
 import shlex
 from shutil import rmtree
 
@@ -61,6 +62,12 @@ def get_tmpfile():
     return path
 
 
+def get_unique_tmp_name():
+    """get a unique file name (not created)"""
+    unique = str(uuid.uuid4())
+    return os.path.join(tempfile.gettempdir(), unique)
+
+
 def remove(path):
     """remove a file/directory/symlink"""
     if not os.path.lexists(path):
diff --git a/tests-ng/transformations.sh b/tests-ng/transformations.sh
index 7fbd005..8c729db 100755
--- a/tests-ng/transformations.sh
+++ b/tests-ng/transformations.sh
@@ -9,6 +9,7 @@
 
 # exit on first error
 set -e
+#set -v
 
 # all this crap to get current path
 rl="readlink -f"
@@ -59,10 +60,16 @@ cfg="${tmps}/config.yaml"
 
 # token
 token="test-base64"
+tokend="compressed archive"
+touched="touched"
 
 cat > ${cfg} << _EOF
 trans:
   base64: cat {0} | base64 -d > {1}
+  uncompress: mkdir -p {1} && tar -xf {0} -C {1}
+trans_write:
+  base64: cat {0} | base64 > {1}
+  compress: tar -cf {1} -C {0} .
 config:
   backup: true
   create: true
@@ -74,43 +81,117 @@ dotfiles:
   f_abc:
     dst: ${tmpd}/abc
     src: abc
-    trans:
-      - base64
+    trans: base64
+    trans_write: base64
+  d_ghi:
+    dst: ${tmpd}/ghi
+    src: ghi
+    trans: uncompress
+    trans_write: compress
 profiles:
   p1:
     dotfiles:
     - f_abc
     - f_def
+    - d_ghi
 _EOF
 cat ${cfg}
 
-# create the dotfile
+# create the base64 dotfile
 tmpf=`mktemp`
-echo ${token}  > ${tmpf}
+echo ${token} > ${tmpf}
 cat ${tmpf} | base64 > ${tmps}/dotfiles/abc
 rm -f ${tmpf}
 
+# create the canary dotfile
 echo 'marker' > ${tmps}/dotfiles/def
 
-# install
-cd ${ddpath} | ${bin} install -f -c ${cfg} -p p1 -b
+# create the compressed dotfile
+tmpx=`mktemp -d`
+mkdir -p ${tmpx}/{a,b,c}
+mkdir -p ${tmpx}/a/{dir1,dir2}
+# ambiguous redirect ??
+#echo ${tokend} > ${tmpd}/{a,b,c}/somefile
+echo ${tokend} > ${tmpx}/a/somefile
+echo ${tokend} > ${tmpx}/b/somefile
+echo ${tokend} > ${tmpx}/c/somefile
+echo ${tokend} > ${tmpx}/a/dir1/otherfile
+tar -cf ${tmps}/dotfiles/ghi -C ${tmpx} .
+rm -rf ${tmpx}
+tar -tf ${tmps}/dotfiles/ghi
 
-# checks
+###########################
+# test install and compare
+###########################
+
+# install
+cd ${ddpath} | ${bin} install -f -c ${cfg} -p p1 -b -V
+
+# check canary dotfile
+[ ! -e ${tmpd}/def ] && exit 1
+
+# check base64 dotfile
 [ ! -e ${tmpd}/abc ] && exit 1
 content=`cat ${tmpd}/abc`
 [ "${content}" != "${token}" ] && exit 1
 
+# check directory dotfile
+[ ! -e ${tmpd}/ghi/a/dir1/otherfile ] && exit 1
+content=`cat ${tmpd}/ghi/a/somefile`
+[ "${content}" != "${tokend}" ] && exit 1
+content=`cat ${tmpd}/ghi/a/dir1/otherfile`
+[ "${content}" != "${tokend}" ] && exit 1
+
 # compare
-cd ${ddpath} | ${bin} compare -c ${cfg} -p p1 -b
+cd ${ddpath} | ${bin} compare -c ${cfg} -p p1 -b -V
 [ "$?" != "0" ] && exit 1
 
-# change file
-echo 'touched' >> ${tmpd}/abc
+# change base64 deployed file
+echo ${touched} > ${tmpd}/abc
 set +e
-cd ${ddpath} | ${bin} compare -c ${cfg} -p p1 -b
+cd ${ddpath} | ${bin} compare -c ${cfg} -p p1 -b -V
 [ "$?" != "1" ] && exit 1
 set -e
 
+# change uncompressed deployed dotfile
+echo ${touched} > ${tmpd}/ghi/a/somefile
+set +e
+cd ${ddpath} | ${bin} compare -c ${cfg} -p p1 -b -V
+[ "$?" != "1" ] && exit 1
+set -e
+
+###########################
+# test update
+###########################
+
+# update single file
+cd ${ddpath} | ${bin} update -f -k -c ${cfg} -p p1 -b -V f_abc
+[ "$?" != "0" ] && exit 1
+
+# test updated file
+[ ! -e ${tmps}/dotfiles/abc ] && exit 1
+content=`cat ${tmps}/dotfiles/abc`
+bcontent=`echo ${touched} | base64`
+[ "${content}" != "${bcontent}" ] && exit 1
+
+# update directory
+echo ${touched} > ${tmpd}/ghi/b/newfile
+rm -r ${tmpd}/ghi/c
+cd ${ddpath} | ${bin} update -f -k -c ${cfg} -p p1 -b -V d_ghi
+[ "$?" != "0" ] && exit 1
+
+# test updated directory
+tar -tf ${tmps}/dotfiles/ghi | grep './b/newfile'
+tar -tf ${tmps}/dotfiles/ghi | grep './a/dir1/otherfile'
+
+tmpy=`mktemp -d`
+tar -xf ${tmps}/dotfiles/ghi -C ${tmpy}
+content=`cat ${tmpy}/a/somefile`
+[ "${content}" != "${touched}" ] && exit 1
+
+# check canary dotfile
+[ ! -e ${tmps}/dotfiles/def ] && exit 1
+
 ## CLEANING
 rm -rf ${tmps} ${tmpd}
 
diff --git a/tests/test_install.py b/tests/test_install.py
index acad9b5..5ebef41 100644
--- a/tests/test_install.py
+++ b/tests/test_install.py
@@ -55,10 +55,8 @@ exec bspwm
                     f.write('    actions:\n')
                     for action in d.actions:
                         f.write('      - {}\n'.format(action.key))
-                if len(d.trans) > 0:
-                    f.write('    trans:\n')
-                    for action in d.trans:
-                        f.write('      - {}\n'.format(action.key))
+                if d.trans_r:
+                    f.write('    trans: {}\n'.format(d.trans_r.key))
             f.write('profiles:\n')
             f.write('  {}:\n'.format(profile))
             for d in dotfiles:
@@ -154,7 +152,7 @@ exec bspwm
         tr = Action('testtrans', cmd)
         f9, c9 = create_random_file(tmp, content=trans1)
         dst9 = os.path.join(dst, get_string(6))
-        d9 = Dotfile(get_string(6), dst9, os.path.basename(f9), trans=[tr])
+        d9 = Dotfile(get_string(6), dst9, os.path.basename(f9), trans_r=tr)
 
         # to test template
         f10, _ = create_random_file(tmp, content='{{@@ profile @@}}')