diff --git a/lib/completion.zsh b/lib/completion.zsh
index 83b6efb66..3a19a4eba 100644
--- a/lib/completion.zsh
+++ b/lib/completion.zsh
@@ -27,9 +27,9 @@ zstyle ':completion:*:*:*:*:*' menu select
 zstyle ':completion:*:*:kill:*:processes' list-colors '=(#b) #([0-9]#) ([0-9a-z-]#)*=01;34=0=01'
 if [ "$OSTYPE[0,7]" = "solaris" ]
 then
-  zstyle ':completion:*:*:*:*:processes' command "ps -u `whoami` -o pid,user,comm"
+  zstyle ':completion:*:*:*:*:processes' command "ps -u $USER -o pid,user,comm"
 else
-  zstyle ':completion:*:*:*:*:processes' command "ps -u `whoami` -o pid,user,comm -w -w"
+  zstyle ':completion:*:*:*:*:processes' command "ps -u $USER -o pid,user,comm -w -w"
 fi
 
 # disable named-directories autocompletion
diff --git a/plugins/systemadmin/systemadmin.plugin.zsh b/plugins/systemadmin/systemadmin.plugin.zsh
index f5e44c66f..e0b1773ad 100644
--- a/plugins/systemadmin/systemadmin.plugin.zsh
+++ b/plugins/systemadmin/systemadmin.plugin.zsh
@@ -30,7 +30,7 @@ function retlog() {
 }
 
 alias ping='ping -c 5'
-alias clr='clear;echo "Currently logged in on $(tty), as $(whoami) in directory $(pwd)."'
+alias clr='clear;echo "Currently logged in on $(tty), as $USER in directory $(pwd)."'
 alias path='echo -e ${PATH//:/\\n}'
 alias mkdir='mkdir -pv'
 # get top process eating memory
diff --git a/themes/adben.zsh-theme b/themes/adben.zsh-theme
index aa3093f64..6869c8a20 100644
--- a/themes/adben.zsh-theme
+++ b/themes/adben.zsh-theme
@@ -89,9 +89,8 @@ function precmd {
 
 # Context: user@directory or just directory
 prompt_context () {
-    local user=`whoami`
-    if [[ "$user" != "$DEFAULT_USER" || -n "$SSH_CLIENT" ]]; then
-        echo -n "${PR_RESET}${PR_RED}$user@%m${PR_RESET}${PR_BRIGHT_YELLOW}%~%<<${PR_RESET}"
+    if [[ "$USER" != "$DEFAULT_USER" || -n "$SSH_CLIENT" ]]; then
+        echo -n "${PR_RESET}${PR_RED}$USER@%m${PR_RESET}${PR_BRIGHT_YELLOW}%~%<<${PR_RESET}"
     else
         echo -n "${PR_RESET}${PR_BRIGHT_YELLOW}%~%<<${PR_RESET}"
     fi
diff --git a/themes/agnoster.zsh-theme b/themes/agnoster.zsh-theme
index 2b33c48bc..7a62bd860 100644
--- a/themes/agnoster.zsh-theme
+++ b/themes/agnoster.zsh-theme
@@ -60,10 +60,8 @@ prompt_end() {
 
 # Context: user@hostname (who am I and where am I)
 prompt_context() {
-  local user=`whoami`
-
-  if [[ "$user" != "$DEFAULT_USER" || -n "$SSH_CLIENT" ]]; then
-    prompt_segment black default "%(!.%{%F{yellow}%}.)$user@%m"
+  if [[ "$USER" != "$DEFAULT_USER" || -n "$SSH_CLIENT" ]]; then
+    prompt_segment black default "%(!.%{%F{yellow}%}.)$USER@%m"
   fi
 }
 
diff --git a/themes/flazz.zsh-theme b/themes/flazz.zsh-theme
index 280794f2b..c0a7fb5d0 100644
--- a/themes/flazz.zsh-theme
+++ b/themes/flazz.zsh-theme
@@ -1,4 +1,4 @@
-if [ "$(whoami)" = "root" ]
+if [ "$USER" = "root" ]
 then CARETCOLOR="red"
 else CARETCOLOR="blue"
 fi
diff --git a/themes/obraun.zsh-theme b/themes/obraun.zsh-theme
index 08d137665..7af44056f 100644
--- a/themes/obraun.zsh-theme
+++ b/themes/obraun.zsh-theme
@@ -1,4 +1,4 @@
-if [ "$(whoami)" = "root" ]; then CARETCOLOR="red"; else CARETCOLOR="blue"; fi
+if [ "$USER" = "root" ]; then CARETCOLOR="red"; else CARETCOLOR="blue"; fi
 
 local return_code="%(?..%{$fg[red]%}%? ↵%{$reset_color%})"
 
diff --git a/themes/re5et.zsh-theme b/themes/re5et.zsh-theme
index 5bded76a3..95af1e2ee 100644
--- a/themes/re5et.zsh-theme
+++ b/themes/re5et.zsh-theme
@@ -1,4 +1,4 @@
-if [ "$(whoami)" = "root" ]; then CARETCOLOR="red"; else CARETCOLOR="magenta"; fi
+if [ "$USER" = "root" ]; then CARETCOLOR="red"; else CARETCOLOR="magenta"; fi
 
 local return_code="%(?..%{$fg_bold[red]%}:( %?%{$reset_color%})"
 
diff --git a/themes/sunrise.zsh-theme b/themes/sunrise.zsh-theme
index 4bea20a1b..28befd01b 100644
--- a/themes/sunrise.zsh-theme
+++ b/themes/sunrise.zsh-theme
@@ -10,7 +10,7 @@ Y=$fg_no_bold[yellow]
 B=$fg_no_bold[blue]
 RESET=$reset_color
 
-if [ "$(whoami)" = "root" ]; then
+if [ "$USER" = "root" ]; then
     PROMPTCOLOR="%{$R%}" PREFIX="-!-";
 else
     PROMPTCOLOR="" PREFIX="---";
diff --git a/themes/ys.zsh-theme b/themes/ys.zsh-theme
index a44f295f4..65448964d 100644
--- a/themes/ys.zsh-theme
+++ b/themes/ys.zsh-theme
@@ -33,7 +33,7 @@ ${git_info} \
 %{$fg[white]%}[%*]
 %{$terminfo[bold]$fg[red]%}$ %{$reset_color%}"
 
-if [[ "$(whoami)" == "root" ]]; then
+if [[ "$USER" == "root" ]]; then
 PROMPT="
 %{$terminfo[bold]$fg[blue]%}#%{$reset_color%} \
 %{$bg[yellow]%}%{$fg[cyan]%}%n%{$reset_color%} \