UNIX for Dummies Questions & Answers

I want to know what's the meaning of the following commands

first eg

Code:

^[^aeiou]*a[^aeiou]*e[^aeiou]*i[^aeiou]*o[^aeiou]*u[^aeiou]*$

What does exactly the *a,*e,*i ...*$ means in this command?
I know that i can also use this command without the *a,*e,*i ... *$!
At this ocassion what's the difference?

second eg

Code:

sed ‘s/^/<tab>/’ file1

In sed command why do we use 's' and what's the meaning of it?
Also in sed when do i have to use the substitude command '1,$s'?

third eg

Code:

sed ‘1,/^$/d’ file1

At this example what does the '^$' means?

In a regular expression the splat (*), some people call it a star, means zero or more of the proceeding character. A simple example, /word */ will match 'word' followed by zero or more spaces. In the example you gave, [^aeiou] will match any character that is not a vowel. [^aeiou]*a will match zero or more non-vowels, followed by the letter 'a'. The same is true for the rest. So a string like hahhehhihhhohhhuhh would match the pattern, but heahehihohu would not since the first vowel is not an a.

The 's' is the substitute command. Anything that matches between the first pair of slant characters will be replaced with the string between the middle and last slant characters. In your example, the beginning of line is replaced with <tab>

The '^' represents the beginning of the buffer, and '$' represents the end of the buffer. When put together, as in your example, it means the beginning and ending of the buffer are next to each other without any characters between (a blank line). This sed deletes blank lines.

Thank you very much for the help!