GREP command : How to use ??

GREP:
Three version of grep command in UNIX 'grep, fgrep, egrep'.
'fgrep' stands for Fixed 'grep'.
'egrep' Extended 'grep'.

1. To find relevant word and exclusion irrelevant word.
# grep Exception logfile.txt | grep -v ERROR

2.If you want to count of a particular word in log file you can use grep -c option to count the word.
# grep -c "Error" logfile.txt

3. grep --context option allows us to print lines around matching pattern. Below example of grep command in UNIX will print 6 lines around matching line of word "successful" in logfile.txt
# grep --context=6 successful logfile.txt
# grep -C 2 'hello' *
Prints two lines of context around each matching line.

4. egrep stands for extended grep and it is more powerful than grep command in Unix and allows more regular exception
# egrep 'Error|Exception' logfile.txt

5. If you want to do case insensitive search than use -i option from grep command in UNIX. Grep -i will find occurrence of both Error, error and ERROR
# grep -i Error logfile

6. Below command will print all files which have "Error" on them. ZGREP used to perform same operation as grep does but with .gz files
# zgrep -i Error *.gz

7. Above grep command in UNIX searches only for instances of 'ERROR' that are entire words; it does not match `SysERROR'.
# grep -w ERROR logfile
# grep 'ERROR>' *
Searches only for words ending in 'ERROR', so it matches the word `SysERROR'.

8. "grep -l" which display only the file names which matches the given pattern. Below command will only display file names which have ERROR
# grep -l ERROR *.log

9. If you want to see line number of matching lines you can use option "grep -n" below command will show on which lines Error has appeared.
# grep -n ERROR log file.

10. If you want to do recursive search using grep command in Unix there are two options either use "-R" command line option or increase directory one by one as shown below.