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Examples about filters, i.e., commands cut, tr, uniq, sort, grep -E (or egrep)

example.txt

408 Rossi Giulia 30.0
12 Rossi Stefania 21.5
234 Bianchi Gianna 17.0
123 Bianchi Bianchi 30.0

example_uniq.txt

Gabriele
Giulia
Stefano
Stefano
Stefano S
Stefania

> cut -d ' ' -f 1,4 example.txt
12 21.5
408 30.0
234 17.0
123 30.0

> cut -d ' ' -f 1-2,4 example.txt 
12 Rossi 21.5
408 Rossi 30.0
234 Bianchi 17.0
123 Bianchi 30.0

> tr -s sn < example.txt
408 Rosi Giulia 30.0
12 Rosi Stefania 21.5
234 Bianchi Giana 17.0
123 Bianchi Bianchi 30.0

> tr -d si < example.txt 
408 Ro Gula 30.0
12 Ro Stefana 21.5
234 Banch Ganna 17.0
123 Banch Banch 30.0

• Replace everything that is not the letter l with the letter X

> echo "hello world" | tr -c l X
XXllXXXXXlXX

• Replace everything that is not a digit with the character -

> echo "Stefano 123 Giulia 345" | tr -c [0-9] -
--------123--------345-

> uniq example_uniq.txt 
Gabriele
Giulia
Stefano
Stefano S
Stefania

> uniq -c example_uniq.txt 
      1 Gabriele
      1 Giulia
      2 Stefano
      1 Stefano S
      1 Stefania

> uniq -d example_uniq.txt 
Stefano

> sort -k1,1n example.txt
12 Rossi Stefania 21.5
123 Bianchi Bianchi 30.0
234 Bianchi Gianna 17.0
408 Rossi Giulia 30.0

> sort -k2,2 example.txt 
123 Bianchi Bianchi 30.0
234 Bianchi Gianna 17.0
12 Rossi Stefania 21.5
408 Rossi Giulia 30.0

> sort -k2,2 -k4,4n example.txt 
234 Bianchi Gianna 17.0
123 Bianchi Bianchi 30.0
12 Rossi Stefania 21.5
408 Rossi Giulia 30.0

> sort -R example.txt 
234 Bianchi Gianna 17.0
123 Bianchi Bianchi 30.0
12 Rossi Stefania 21.5
408 Rossi Giulia 30.0

(the egrep command behaves as grep -E, i.e., it makes use of extended-regex ERE)

> egrep -e "[2468]\>" example.txt 
408 Rossi Giulia 30.0
12 Rossi Stefania 21.5
234 Bianchi Gianna 17.0

> egrep -e "^[2468]\>" -e "^[1-9][0-9]*[02468]\>" example.txt 
408 Rossi Giulia 30.0
12 Rossi Stefania 21.5
234 Bianchi Gianna 17.0

> egrep -n -e "Bianchi" example.txt 
3:234 Bianchi Gianna 17.0
4:123 Bianchi Bianchi 30.0

> egrep -n -v -e "Bianchi" example.txt 
1:408 Rossi Giulia 30.0
2:12 Rossi Stefania 21.5

> egrep -H -A 1 -B 0 -e "^12\>" example.txt 
example.txt:12 Rossi Stefania 21.5
example.txt-234 Bianchi Gianna 17.0

> egrep -e "1[8-9]\.[0-9]" -e "2[0-9]\.[0-9]$" -e "30\.0$" example.txt |cut -d ' ' -f 1-2,4|sort -k2,2r
408 Rossi 30.0
12 Rossi 21.5
123 Bianchi 30.0