diff --git a/aliases.zsh b/aliases.zsh
index 9981c99..84e92a3 100644
--- a/aliases.zsh
+++ b/aliases.zsh
@@ -1,8 +1,16 @@
+#! /bin/zsh
+
 alias cdiff="colordiff"
 
-[ -x "$(which gpg2)" ] && alias clean-gpg="for a in `gpg2 -k | sed -rn 's/pub +[a-z0-9]+\/(0x[0-9A-Fa-f]+).*/\1/p'`; do gpg2 --quiet --no-tty --edit-key $a clean save; done;"
+function clean-gpg () {
+    [ -z "$(command -v gpg2)" ] && exit 1;
+    for key in $(gpg2 -k | sed -rn 's/pub +[a-z0-9]+\/(0x[0-9A-Fa-f]+).*/\1/p');
+    do
+        gpg2 --quiet --no-tty --edit-key "$key" clean save
+    done
+}
 
-alias diff="diff -W $(( $(tput cols) - 2))"
+alias diff="diff -W \$(( \$(tput cols) - 2))"
 
 alias bz2c='bzip2 --best'
 alias gzc='gzip --best --no-name'
@@ -20,7 +28,8 @@ alias urlencode='python3 -c "import sys, urllib.parse as ul; [sys.stdout.write(u
 
 function mkcdir () {
     mkdir -p -- "$1" &&
-    cd -P -- "$1"
+        cd -P -- "$1" ||
+        exit 1
 }
 
 function chrooted() {
@@ -32,13 +41,19 @@ function chrooted() {
     else
         echo "We are chrooted."
     fi
+
+    # shellcheck disable=SC2046
+    # Word splitting *cannot* occur in a result of `test`
     return $(test "$ROOT_MP" -eq "$SHELL_MP")
 }
 
 if [ -x "$(which lsb_release)" ];
 then
-    current_dist=`lsb_release -c -s`
-    all_dkms_packages="`apt-cache rdepends --installed dkms | sed -rn 's/^ +([^ ]+)$/\1/p' | sort -iu | tr '\n' ' '`"
+    current_dist="$(lsb_release -c -s)"
+    all_dkms_packages="$(apt-cache rdepends --installed dkms | sed -rn 's/^ +([^ ]+)$/\1/p' | sort -iu | tr '\n' ' ')"
+
+    # shellcheck disable=SC2154,2086
+    # both errors are irrelevant as we are part of a bigger infrastructure
     if [ $use_sudo -eq 1 ];
     then
         alias aar='sudo apt-get --purge autoremove'
diff --git a/browser.zsh b/browser.zsh
index 716d506..fbafbbf 100644
--- a/browser.zsh
+++ b/browser.zsh
@@ -1,6 +1,9 @@
-function duckduck() { elinks -dump "https://duckduckgo.com/?q=`escape "$@"`"; }
-function escape() { perl -MURI::Escape -e 'print uri_escape($ARGV[0]);' "$@"; }
-function google() { elinks -dump "https://www.google.de/search?q=`escape "$@"`"; }
+#! /bin/zsh
 
-function wetter() { curl --tr-encoding -H "Accept-Language: ${LANG%_*}" "https://wttr.in/$@"; }
-function wetter2() { curl --tr-encoding -H "Accept-Language: ${LANG%_*}" "https://v2.wttr.in/$@"; }
+function escape() { perl -MURI::Escape -e 'print uri_escape($ARGV[0]);' "$@"; }
+
+function duckduck() { elinks -dump "https://duckduckgo.com/?q=$(escape "$@")"; }
+function google() { elinks -dump "https://www.google.de/search?q=$(escape "$@")"; }
+
+function wetter() { curl --tr-encoding -H "Accept-Language: ${LANG%_*}" "https://wttr.in/$*"; }
+function wetter2() { curl --tr-encoding -H "Accept-Language: ${LANG%_*}" "https://v2.wttr.in/$*"; }
diff --git a/exa.zsh b/exa.zsh
index e9e1f16..3f36d49 100644
--- a/exa.zsh
+++ b/exa.zsh
@@ -1,3 +1,5 @@
+#! /bin/zsh
+
 alias exa='exa -FHhg@ --git --time-style long-iso'
 alias exal='exa -l'
 function exat() {
diff --git a/local-bin.zsh b/local-bin.zsh
index 7738783..1769729 100644
--- a/local-bin.zsh
+++ b/local-bin.zsh
@@ -1,5 +1,6 @@
+#! /bin/zsh
 # Make sure we include this file only once
-if [ -z $ZSH_LOCAL_BIN_ALREADY_SET ];
+if [ -z "$ZSH_LOCAL_BIN_ALREADY_SET" ];
 then
         export ZSH_LOCAL_BIN_ALREADY_SET=1
         # set PATH so it includes user's private bin if it exists