[SOLVED] How to remove a word prefix using grep?

Issue

How can I remove the beginning of a word using grep? For example, I have a file that contains this:

www.abc.com

I only need the this part:

abc.com

Sorry for the basic question, but I have no experience with Linux.

Solution

You don't edit strings with grep in Unix shell, grep is usually used to find or remove some lines from the text. You'd rather use sed instead:

$ echo www.example.com | sed 's/^[^\.]\+\.//'
example.com

You'll need to learn regular expressions to use it effectively.

Sed can also edit file in-place (modify the file), if you pass -i argument, but be careful, you can easily lose data if you write the wrong sed command and use -i flag.

An example

From your comments guess you have a TeX document, and your want to remove the first part of all .com domain names. If it is your document test.tex:

\documentclass{article}
\begin{document}
www.example.com
example.com www.another.domain.com
\end{document}

then you can transform it with this sed command (redirect output to file or edit in-place with -i):

$ sed 's/\([a-z0-9-]\+\.\)\(\([a-z0-9-]\+\.\)\+com\)/\2/gi' test.tex 
\documentclass{article}
\begin{document}
example.com
example.com another.domain.com
\end{document}

Please note that:

• A common sequence of allowed symbols followed by a dot is matched by [a-z0-9-]\+\.
• I used groups in the regular expression (parts of it within \( and \)) to indicate the first and the second part of the URL, and I replace the entire match with its second group (\2 in the substitution pattern)
• The domain should be at least 3rd level .com domain (every \+ repition means at least one match)
• The search is case insensitive (i flag in the end)
• It can do more than match per line (g flag in the end)

Answered By - sastanin

Answer Checked By - Marie Seifert (WPSolving Admin)