Below are some examples on the usage of grep and egrep in Unix.
We are using file text.txt as our source file.

Content of text.txt
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one
two
three
four
five
six
seven
eight
nine
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To print NUM lines of trailing context after matching lines.
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[root@server:~] $grep -A<NUM of lines> <pattern> <file>
[root@server:~] $grep -A2 six text.txt
six
seven
eight
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To print NUM lines of leading context before matching lines.
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[root@server:~] $grep -B<NUM of lines> <pattern> <file>
[root@server:~] $grep -B2 six text.txt
four
five
six
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To print all except lines matching pattern.
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[root@server:~] $grep -v <pattern> <file>
[root@server:~] $grep -v six text.txt
one
two
three
four
five
seven
eight
nine
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Using egrep to print lines matching either pattern.
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[root@server:~] $grep -v '<pattern1>|<pattern2>' <file>
[root@server:~] $egrep 'six|seven' text.txt
six
seven
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