RegularExpressions

Regular expressions consist of tree parts:

* atoms

Atoms specify what text should be found

Atoms could be a single characters, a range of characters or dot if you don't know the character. Atoms could be a class ( [[:alpha:]], [[:upper:]], [[:alnum:]])

* repetition operator

Specify how many times character should occur

• {n} - exact n time
• {n,} - minimal n time
• {,n} - n time max
• {n,o} - between n and o times
• * - zero or more times
• + - one or more times
• ? - zero or one time

* place operator

Specify where to find the next character

• ^ - beginning of the line
• $ - end of the line
• \< - beginning of a word
• \> - end of a word
• \A - start of a file
• \Z - end of a file

* Examples

Searching in text file regfile with grep