[Linux] Line and word anchors by using grep tool

[Linux] Line and word anchors by using grep tool

 

The ^ anchor specifies that the pattern following it should be at the start of the line:

[manish@clone ~]$ grep '^th' testfile this

The $ anchor specifies that the pattern before it should be at the end of the line.

[manish@clone ~]$ grep 'i$' testfile Hi

The operator \< anchors the pattern to the start of a word.

[manish@clone ~]$ grep '\<fe' testfile to carry out few regular expressions

Similarly, \> anchors the pattern to the end of a word.

[manish@clone ~]$ grep 'le\>' testfile is test file

The \b (word boundary) anchor can be used in place of \< and \> to signify the beginning or end of a word:

[manish@clone ~]$ grep -e '\breg' testfile to carry out few regular expressions

Finally, we look at the | (alternation) operator, which is part of the extended regex features. A pattern containing this operator separately matches the parts on either side of it; if either one is found, the line containing it is a match. The parts can themselves be complex regular expressions, so this means you can check each line in a file for multiple search patterns in one pass.

[manish@clone ~]$ grep -E 'hi|bc' testfile this Abcd

That was pretty simple; so let’s try a more complicated one. Can you reason out why the output lines for this regex are as shown below?

[manish@clone ~]$ grep -E '^[t-z]+|[^a-z]+$' testfile

this

to carry out few regular expressions

123 456

ABCD

 

Reference :

• 
  A Beginner’s Guide to Grep: Basics and Regular Expressions