Bash string comparison using “if”

”==” and ”!=” only can be used in case of string comparison.

if [ "$STRING" == "abc" ];then
    echo "STRING is abc!"
fi 

or

if [ "$STRING" = "abc" ];then
    echo "STRING is abc!"
fi 

Appendix. References

• General : http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_01.html