Differences

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+====== Filters ======
+Return to [[os:|Operating Systems Course]]
+Examples about filters, i.e., commands ''cut'', ''tr'', ''uniq'', ''sort'', ''grep -E'' (or ''egrep'')
+===== Example files =====
+<code txt example.txt>
+Rossi Giulia 30.0
+Rossi Stefania 21.5
+Bianchi Gianna 17.0
+Bianchi Bianchi 30.0
+</code>
+<code txt example_uniq.txt>
+Gabriele
+Giulia
+Stefano
+Stefano
+Stefano S
+Stefania
+</code>
+===== ''cut'' command =====
+<code bash>
+> cut -d ' ' -f 1,4 example.txt
+21.5
+30.0
+17.0
+30.0
+</code>
+<code bash>
+> cut -d ' ' -f 1-2,4 example.txt
+Rossi 21.5
+Rossi 30.0
+Bianchi 17.0
+Bianchi 30.0
+</code>
+===== ''tr'' command =====
+<code bash>
+> tr -s sn < example.txt
+Rosi Giulia 30.0
+Rosi Stefania 21.5
+Bianchi Giana 17.0
+Bianchi Bianchi 30.0
+</code>
+<code bash>
+> tr -d si < example.txt
+Ro Gula 30.0
+Ro Stefana 21.5
+Banch Ganna 17.0
+Banch Banch 30.0
+</code>
+  * Replace everything that is **not** the letter ''l'' with the letter ''X''
+<code bash>
+> echo "hello world" | tr -c l X
+XXllXXXXXlXX
+</code>
+  * Replace everything that is **not** a digit with the character ''-''
+<code bash>
+> echo "Stefano 123 Giulia 345" | tr -c [0-9] -
+--------123--------345-
+</code>
+===== ''uniq'' command =====
+<code bash>
+> uniq example_uniq.txt
+Gabriele
+Giulia
+Stefano
+Stefano S
+Stefania
+</code>
+<code bash>
+> uniq -c example_uniq.txt
+Gabriele
+Giulia
+Stefano
+Stefano S
+Stefania
+</code>
+<code bash>
+> uniq -d example_uniq.txt
+Stefano
+</code>
+===== ''sort'' command =====
+<code bash>
+> sort -k1,1n example.txt
+Rossi Stefania 21.5
+Bianchi Bianchi 30.0
+Bianchi Gianna 17.0
+Rossi Giulia 30.0
+</code>
+<code bash>
+> sort -k2,2 example.txt
+Bianchi Bianchi 30.0
+Bianchi Gianna 17.0
+Rossi Stefania 21.5
+Rossi Giulia 30.0
+</code>
+<code bash>
+> sort -k2,2 -k4,4n example.txt
+Bianchi Gianna 17.0
+Bianchi Bianchi 30.0
+Rossi Stefania 21.5
+Rossi Giulia 30.0
+</code>
+<code bash>
+> sort -R example.txt
+Bianchi Gianna 17.0
+Bianchi Bianchi 30.0
+Rossi Stefania 21.5
+Rossi Giulia 30.0
+</code>
+===== ''grep -E'' or ''egrep'' commands =====
+(the ''egrep'' command behaves as ''grep -E'', i.e., it makes use of extended-regex ERE)
+<code bash>
+> egrep -e "[2468]\>" example.txt
+Rossi Giulia 30.0
+Rossi Stefania 21.5
+Bianchi Gianna 17.0
+</code>
+<code bash>
+> egrep -e "^[2468]\>" -e "^[1-9][0-9]*[02468]\>" example.txt
+Rossi Giulia 30.0
+Rossi Stefania 21.5
+Bianchi Gianna 17.0
+</code>
+<code bash>
+> egrep -n -e "Bianchi" example.txt
+:234 Bianchi Gianna 17.0
+:123 Bianchi Bianchi 30.0
+</code>
+<code bash>
+> egrep -n -v -e "Bianchi" example.txt
+:408 Rossi Giulia 30.0
+:12 Rossi Stefania 21.5
+</code>
+<code bash>
+> egrep -H -A 1 -B 0 -e "^12\>" example.txt
+example.txt:12 Rossi Stefania 21.5
+example.txt-234 Bianchi Gianna 17.0
+</code>
+<code bash>
+> 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
+Rossi 30.0
+Rossi 21.5
+Bianchi 30.0
+</code>

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