Regular expressions

SED

Character	Description
^	Matches the beginning of the line
$	Matches the end of the line
.	Matches any single character
*	Will match zero or more occurrences of the previous character
[ ]	Matches all the characters inside the [ ]

Regular expression	Description
/./	Will match any line that contains at least one character
/../	Will match any line that contains at least two characters
/^#/	Will match any line that begins with a '#'
/^$/	Will match all blank lines
/}$/	Will match any lines that ends with '}' (no spaces)
/} *$/	Will match any line ending with '}' followed by zero or more spaces
/[abc]/	Will match any line that contains a lowercase 'a', 'b', or 'c'
/^[abc]/	Will match any line that begins with an 'a', 'b', or 'c'

SED Examples
sed -i ’s/Ben/Dave/g’ file.txt # Replace all the words Ben for the word Dave
sed 's/Ben|ben/Dave/g' file.txt # Replace all the words Ben and ben for the word Dave
sed 's/^[ ^t]*//' file.txt # Delete all spaces in front of every line of file.txt
sed 's/[ ^t]*$//' file.txt # Delete all spaces at the end of every line of file.txt
sed -e '/^#/d' file.txt | more # View file without the commented lines
sed -e '/regexp/d' file.txt # delete the word regexp
sed 's/...//' # delete the first 3 characters on every line

AWK
awk '!($0 in a){a[$0];print}' # Remove duplicate, nonconsecutive lines
awk '{ print $NF }' # print the last field of each line
awk -F':' '{print $3,$4;}' # show only what is on columns 3 and 4
Find and replace
awk '{gsub(/foo/,"bar")}; 1' # if foo replace by bar
awk '/baz/{gsub(/foo/, "bar")}; 1' # ONLY for lines which contain "baz"
awk '!/baz/{gsub(/foo/, "bar")}; 1' # EXCEPT for lines which contain "baz"

Grep
grep 'word\|logs' file # can contain 2 strings
grep "word1" file | grep "word2" # line must match the 2 strings 

xargs Examples
locate file* | xargs grep "bob" # find a file and grep a string
locate file* | xargs rm # find a file a del it

CUT
cut -d " " -f 1 - cut everything after the first word

For loop example