GREP

Features:
1. The ability to parse lines based on text and/or RegExes
2. Post-processor
3. Searches case-sensitively, by default
4. Searches for the text anywhere on the line


1. grep 'linux' grep1.txt
2. grep -i 'linux' grep1.txt - case-insensitive search
3. grep '^linux' grep1.txt - uses '^' anchor to anchor searches at the beginning of lines
4. grep -i '^linux' grep1.txt
5. grep -i 'linux$' grep1.txt - uses '$' anchor to anchor searches at the end of lines

Note: Anchors are RegEx characters (meta-characters). They're used to match at the beginning and end of lines

6. grep '[0-9]' grep1.txt - returns lines containing at least 1 number
7. grep '[a-z]' grep1.txt


8. rpm -qa | grep grep - searches the package database for programs named 'grep'

9. rpm -qa | grep -i xorg | wc -l - returns the number of pacakges with 'xorg' in their names

10. grep sshd messages
11. grep -v sshd messages - performs and inverted search (all but 'sshd' entries will be returned)
12. grep -v sshd messages | grep -v gconfd
13. grep -C 2 sshd messages - returns 2 lines, above and below matching line

Note: Most, if not all, Linux programs log linearly, which means one line after another, from the earliest to the current

Note: Use single or double quotes to specify RegExes
Also, execute 'grep' using 'egrep' when RegExes are being used