===== bash: "How To" ... utilize tests =====
^operation^what^code^
|string|variable equal to "__xyz__"|if [ $STR == "__xyz__" ]|
|:::|variable unequal to "__xyz__"|if [ $STR != "__xyz__" ]|
|:::|variable contains substring "__xyz__"|if %%[[%% $STR =~ "__xyz__" %%]]%%|
|:::|variable is in list "__abc__" or "__def__" (or ...)|if %%[[%% $STR =~ %%^%%("__abc__"%%|%%"__def__")$ %%]]%%|
|integer|variable equal to __n__|if [ $STR -eq __n__ ]|
|file|"__node__" exists \\  (whatever type i.e. file, folder, ...)|if [ -e "__node__" ]|
|:::|regular "__filename__" exists|if [ -f "__filename__" ]|
|:::|create unique temporary file|touch /tmp/$$.tmp|
|:::|find file "__filename__" with numerically \\  largest extension in folder|ls -1d "__filename__.*" %%|%% cut -d "." -f 2 %%|%% sort -rg %%>%% /tmp/$$.tmp  \\  MAX=$(head -n 1 /tmp/$$.tmp)| 
|execution|result of command execution|RSLT=$?|
|:::|being root|if ($(id -u) -eq 0))|

//work in progress//