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g/re/p
Global search specified by /re/ and print
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grep "string" filename
	search for string in filename. print matching line
grep 're' filename
	search for regular expression in file name. print matching line
        note that "re" is NOT enclosed by  "/" (as in sed)
grep -R pattern * 
	recursive search for pattern from curent level and below
grep -v pattern infile
	display lines which do NOT match pattern

grep -i pattern infile
	display lines which match pattern regardless of case 
grep -n pattern infile
	display matched line(s) followed by the line number(s) 
grep -c pattern infile
	count number of occurrences of pattern in "infile"

grep -l pattern file*
	display the names of files containing pattern
grep -o pattern infile
	displays not the line but the matches to pattern
grep -e pattern file
	useful when pattern contains "-" 
grep -e pattern1 -e pattern2 file
	specify multiple patterns for searching


%-------contextual search-----------------------------------------------
grep -A n pattern infile
	display matched line and "n" lines AFTER matched line 
grep -B n pattern infile
	display matched line and "n" lines BEFORE matched line 
grep -C n pattern infile
	display matched line and "n" lines CENTERED on matched line 
%-----------------------------------------------------------------------


grep -w pattern infile
	display lines containing word stated by pattern 
grep \<pattern\> infile
	does the same as as "-w"
grep pattern\> infile
	display lines in which word ending is given by pattern
grep \<pattern infile
	display lines in which word beginning is given by pattern

grep -x pattern infile
	display if pattern matches entire line

%------------------------------------------------------------------------
Differences between ordinary grep and grep with extended reg expression
%------------------------------------------------------------------------

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grep     	grep -E
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a\+      	a+
a\?      	a?
exp1\|exp2  	exp1|exp2
\{m,n\}  	{m,n}
{\n,\}   	{n,}
\{m\}		{m}

%search for "foo" in files (recursively)
find . -type f -exec grep -il 'foo' {} \;

%search for "parvi" and "foo" 
grep "parvi" $(find . -type f -exec grep -il 'foo' {} \;)  %not vetted
Check out https://alvinalexander.com   for more details

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grep: arcana
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grep pattern one_file
	prints the matched lines but not the file name
grep pattern files
	prints the matched lines and file names
grep pattern one_file /dev/null
	prints the matched lines and file name