egrep

A variation of the grep command is egrep, which stands for extended grep. egrep extends the basic functions of grep by providing full regular expressions. Full regular expressions are more complex regular expressions that can do the following:

• Search for several patterns at a time in an either-or condition

• Use a file containing patterns as the basis for its search

egrep uses the same set of regular expression metacharacters for its search patterns as grep, but egrep also includes the following additional metacharacters:

• str1|str2 Use the pipe (|) to match str1 or str2

• () Treat the text as a group

Here’s how they work. In the following example, I’ll use egrep to search for two different patterns at once, as follows:

egrep 'bcalkins|sburge' file1 <cr> 

The following lines are displayed:

bcalkins        Bill Calkins    ext. 123        Engineering 
sburge          Steve Burge     ext. 234        IT 

Multiple patterns can be supplied using multiple pipes. Another option with egrep is to put the search pattern into a file. I have a file named patterns that contains the following entries:

(bcalkins|wcalkins) 
(burge|Bill) 

When included in a file, the search patterns do not require quotes, but you must enclose them in parenthesis. Now when I execute egrep, I supply the filename containing the search pattern as follows:

egrep –f patterns * <cr> 

All files are searched, and the results are displayed as follows:

file1:bcalkins      Bill Calkins    ext. 123        Engineering 
file1:wcalkins      William Calkins ext. 123        Engineering 
file1:sburge        Steve Burge     ext. 234        IT 
patterns:(bcalkins|wcalkins) 
patterns:(burge|Bill) 
userlist:bcalkins   Bill Calkins    ext. 123        Engineering 
userlist:sburge     Steve Burge     ext. 234        IT