add nix-update alias

dot_bashrc

@@ -17,8 +17,6 @@ HISTFILE=/dev/null
 bind '"\e[A":history-search-backward'
 bind '"\e[B":history-search-forward'
 
-
-
 # check the window size after each command and, if necessary,
 # update the values of LINES and COLUMNS.
 shopt -s checkwinsize
@@ -103,16 +101,25 @@ alias rm='rm --interactive --verbose'
 alias mv='mv --interactive --verbose'
 alias cp='cp --verbose --interactive'
 
-alias wget='wget -c'
+if hash wget 2>/dev/null; then
+  alias wget='wget -c'
+fi
+
 alias dmesg='dmesg -T'
 alias grep='grep --color'
 
-alias serve="python3 -m $(python3 -c 'import sys; print("http.server" if sys.version_info[:2] > (2,7) else "SimpleHTTPServer")')"
+if hash python3 2>/dev/null; then
+  alias serve="python3 -m $(python3 -c 'import sys; print("http.server" if sys.version_info[:2] > (2,7) else "SimpleHTTPServer")')"
+fi
 
-alias ta='tmux attach'
-alias tkill="for s in \$(tmux list-sessions | awk -F ':' '{print \$1}' | fzf); do tmux kill-session -t \$s; done;"
+if hash tmux 2>/dev/null; then
+  alias ta='tmux attach'
+  alias tkill="for s in \$(tmux list-sessions | awk -F ':' '{print \$1}' | fzf); do tmux kill-session -t \$s; done;"
+fi
 
-alias tiga='tig --all'
+if hash tig 2>/dev/null; then
+  alias tiga='tig --all'
+fi 
 
 if hash fd 2>/dev/null; then
   alias fdfind='fd'
@@ -122,6 +129,10 @@ if command -v most > /dev/null 2>&1; then
     export PAGER="most"
 fi
 
+if hash nix-env 2>/dev/null; then
+  alias nix-update='nix-channel --update && nix-env -u'
+fi
+
 # ---------------------------------------------------------------------------
 #  COMPLETIONS
 # ---------------------------------------------------------------------------