pattern-matching.txt

Pattern Matching


GREP
grep -r pattern dir
	--grep recursively for pattern in any file nested in dir
egrep '(this|that)' file
OR
grep -e '(this|that)' file
	-grep against target file basic regex accepting patterns using basic regex
egrep '[^\ ]\{8,\}' target
	-pattern-match all 8+ digit chars

SED
sed 's/[[:space:]]//g'
	-trim whitespaces from a file

AWK
awk 'NR==FNR{a[$0];next}!($0 in a)' file2 file1
	--Compare 2 files and return the unique lines in first file
awk NF -
	--remove newlines from stdin
awk 'match($0,"="){print substr($0,RSTART-5,5)}'
	-print characters before+after a pattern is matched
awk  -F":" '{print $2}' file.txt
awk  -F":" '{if ($2)print $2}' file.txt
	-print second colum of ":"-delimited lines in a file
awk -F, '{ print $1 "-" $3 "-" $5 }' file.csv
	-print alternating lines of a csv file
awk -F: '{ print $NF }' file.txt
	-print last column of delimited text file
awk  -F":" '/regex_here/{print $2}' file.txt
	-print second field of lines matching regex from delimited file
awk '/exp/,/end/' file.txt
	-print all lines in a file from match "exp" to match "end"
awk '!/regex/{print $1 " " $2 }' file.txt
	-print all lines not matching regex from first two whitespace-delimited fields
awk '/regex/&&!/regex2/{print $1}' file.txt
	-print all lines matching regex while not matching regex2
awk '{print length, $0}' file.txt | sort -n | cut -d " " -f2-
	-sort wordlists by length


xclip -selection clipboard -o | sed 's/[[:space:]]//g' | awk NF - >http_response_codes.txt
	--remove all whitespace and newlines from a copied selection of text (from clipboard)

	
Bash variables
${var% *}
	--match all characters preceding whitespace
${var##/*}
	--match all characters following "/"
if [[ "${var}" != "${var% *}" ]]; then
	--conditional operation testing if string variable contains whitespace