Filters : 

sort – sort all input in order by some key : 

·         -f fold upper and lower case together
·         -n numeric order instead of text order
·         -k# column number to sort by
·         Example: sort –nk2 file1 file2
·         Remember it will sort as many files as you give so: sort filea fileb filec puts all 3 files together in a sorted list

uniq  - deal with duplicate lines :

·         -c tells how many times a line is repeated
·         -d print only lines that are duplicates of the lines above them
·         -u prints only lines that are not the duplicate of the line above them
·         Example: sort file1 file2 | uniq -d
·         Remember to sort when you want duplicates anywhere within the list considered

comm – compare files listing files in columns next to each other

if given 2 sorted lists, it will create 3 columns: (Use –column number to suppress a particular column)

·         1 : only in the first file given
·         2 : only in the second file given
·         3 : those in both files
·         Example: comm -3 <(sort -n csc270file) <(sort -n csc271file)

tr – translates characters from one given set to another set

·         tr a-z A-Z file : makes uppercase
·         tr ab 12 file : changes all a’s to 1 and b’s to 2
·         tr –c ab 1 file : changes everything but a and b to 1
·         tr –s ab 12 file : changes all a, aa or a…a to 1 and b,bb or b..b to 2