if test options and it usage In Linux

if test (expression)

if test !(expression)

if test expression1 -a expression2 

if test expression1 -o expression2

if test -z STRING 

if test STRING1 = STRING2 

if test STRING1 != STRING2

if test INTEGER1 -eq INTEGER2 

if test INTEGER1 -ge INTEGER2 

if test INTEGER1 -gt INTEGER2 

if test INTEGER1 -lt INTEGER2

if test INTEGER1 -le INTEGER2 

if test INTEGER1 -ne INTEGER2 

if test file1 -nt file2                    # -nt :- newer than 

if test file1 -ot file2                    # -ot :- older than

if test -f file                                # if file exists 

if test -d directory_name           # if directory exists 

if test -x file                               # if file is executable 

if test -r  file                               # if file is readable 

if test -w file                               # if file is writable 

if test -s "filename.txt"; then

    # Code to execute if the file is not empty

else

    # Code to execute if the file is empty or does not exist

fi

if ! test -s "filename.txt"; then

    # Code to execute if the file is empty or does not exist

else

    # Code to execute if the file is not empty

fi

if test -n "$myString"; then

    # Code to execute if the string is not empty

else

    # Code to execute if the string is empty

fi

if ! test -n "$myString"; then

    # Code to execute if the string is empty

else

    # Code to execute if the string is not empty

fi