Grep Commands
1) To search a pattern with only first character/word of every line in a file
grep '^ first-charachter/word ' filename
example : grep '^jan' /home/user/montss.txt
2) To search a pattern with only the last charachter/ word of every line in a file
grep 'character/word$' filename
example : grep 'dec$' /home/user/months.txt
search last character or word in a file
3) To ignore the case of letter use '-i' switch to do so.
grep -i 'Aug' /sample.txt
It will ignore the upper case of Aug in file sample.txt
4) To search in a file in except that word(remove) of the command just use '-v'
grep-v
'Aug' /sample.txt
It will search all line without containing 'Aug' in file sample.txt
5) To count the outlput lines in your grep command use '-c'
grep '-c'
'Aug' /sample.txt
It will show you the counts of lines which have word 'Aug'
6) To list the file names which have the matching pattern
grep -l
'Aug' sample.txt example.txt
It will tell you in which file the 'Aug' pattern contain. if you want to invert the output just use L
7) To list the output of matching pattern with number series
grep -n
'Aug' /sample.txt
It will give output with assigned number series
8) To hide the file name from your output of matching pattern
grep -h 'Aug' /sample.txt
9) To serch a compelete word in a file
grep -w 'keyword' filepath
10)search recursively in a folder or sub folders
grep -r 'keyword' filepath
11) search include line after the keyword
grep -i -A1 'keyword' filepath
e.g grep -i -A1 'ntp' /etc/passwd
It will search line include after the word 'ntp'
12) search include line before the keywords
grep -i -B2 'keyword' filepath
12) search include after and before (combine both) the keyword
grep -i -C3 'keyword ' filepath
13) search for special character (which system know as regular expression) for example literally a dot (.)
grep -i
'\.' filepath
use back slash for your search because if we dont use backslash it will assume as regular expression keyword
Advance Uses of 'grep'
grep -E '^[A-Za-z]{3}.*@[A-Za-z].*\.(com|org|net|tv)'
This is an example of searching all valid email ids which must should start with 3 alphabets(low/upper case) then after (@) all characters should be alphabets then domain can be com,org,net,tv.
> grep = global regular expression print
> -E = Expression
>'' = pattern with in our search
^ = carat character for our search for first character
[A-Za-z] = search only for upper or lower case word a to z
{3} = how many number of times [letter] will search
. = any character
* = zero or many times for characters
@ = regular letter which we will search in our pattern
\. = \ use to print the meta charchter dot (.)
() = with in the brackets a word which we are searching in our patter , using pipe mentions many words
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