Anchors
Beginning of line
A search can be constrained to find the string at the beginning of the line with the symbol ^. Example:
grep '^A' filename
Finds the string A at the beginning of lines.
End of line
A search can be constrained to find the string at the end of the line with the symbol $. Example:
grep '5$' filename
Finds the string 5 at the end of lines.
Counting empty lines
The combination search string ^$ finds empty lines.
To match any single character
The meta-character . matches any single character except the end of line character.
Example
The input file contains these lines:
one
bone
throne
clone
We search with
grep '.one' filename
The results are
bone
throne
clone
The first line doesn't match.
To match zero or more characters
The meta-character * matches zero or more occurences of the previous character.
Example
The input file bells containes these lines
bel
bell
belll
be
bet
We search with
grep 'bel*' bells
The results are
bel
bell
belll
be
bet
Example
The input file is as the previous example. The . is used after the * to require at least a single character.
We search with
grep 'bel*.' bells
The results are
bel
bell
belll
Contrast this with the previous example. Here, we match everything except be.
Example
The input file is as before.
We search with
grep 'bel.*' bells
The results are
bel
bell
belll
Character lists
You can use a list of characters surrounded by [ and ] which will match on any single character in the list.
Example
The input file is lines:
This is the zero line
Here y
Crosses x
we search with
grep [xyz] lines
The result is
This is the zero line
Here y
Crosses x
Example
The input file is as before.
we search with
grep [xyb] lines
The result is
Here y
Crosses x