Sometimes when you run your script there was an error like this:
[email protected]$ ./script.sh bash: ./script.sh: /bin/sh^M: bad interpreter: No such file or directory
Thats because there are one or many ^M character in your script for every newline. This is because you make/edit your script in Windows environment. Text documents that come from a Windows system won’t always play nice in Linux. The converse is true however. If you create a text file in Linux, many programs will fail to recognize the single LF as a newline and will render the document without any line breaks.
To fix that error you can use dos2unix script to convert that file into unix file. These programs basically do exactly what their name implies: dos2unix takes a file and converts all DOS-style newlines to Unix-style newlines. unix2dos takes a file and converts all Unix-style newlines to DOS-stlye newlines.
To install dos2unix in Ubuntu:
sudo apt-get install tofrodos
To install dos2unix in Centos:
yum install dos2unix
dos2unix [files] dos2unix script.sh dos2unix *.php
More info: dos2unix manual page.