Recipe: Comparisons and tests

if and else 
============
if condition; 
then
commands;
else if condition; then
commands;
else
commands;
fi


Conditional execution
=====================
[ condition ] && action; # action executes if condition is true.

[ condition ] || action; # action executes if condition is false.


Test of exist of file
=====================
fpath="/etc/passwd"
if [ -e $fpath ]; then 
echo File exists; 
else 
echo Does not exist; 
fi

Equality
========
if  [ $var -eq 0 ]; then echo "True"; fi
can be written as
if  test $var -eq 0 ; then echo "True"; fi