command_line_pipes
Know Your Pipes and Filters
Pipes and filters are everywhere. Not just in your homes but also in the terminal.
What is a Filter? ䷜
A filter takes input from one command, does some processing, and gives output.
Why filter data? 🗂
Filtering is useful when you want to extract specific information from large amounts of data. It doesn’t remove or modify any data; it just displays a subset of data on the screen. Sometimes we use pipes to filter complex data.
What is a Pipe? 🚰
The symbol ‘|’ denotes a pipe. It is a command that takes an output of one command and feeds it as an input to the second command. You can combine two or more commands and run them consecutively with pipes.
Syntax:
Suppose we have a sample.txt file with the following data:
Let’s filter some data!
😸 cat : Displays the contents of the file.
⫷ less: Shows you only one scroll length of content at a time.
⥱ grep: Takes an argument as string and will find the matching string, if found it will return the matching string else will return nothing.
Following options can be used with grep command:
-v → Shows all the lines that do not match the searched string
-c → Displays only the count of matching lines
-n → Shows the matching line and its number
-i → Match both (upper and lower) case
-A(num) → Print NUM lines of trailing context after matching lines.
-B(num) → Print NUM lines of leading context before matching lines.
-C(num) → Print NUM lines of output context.
-v
-c
-n
-i
-A(num)
-B(num)
-C(num)
⋛ sort: Sorts out the contents of a file.
Following options can be used with sort command:
-r → Reverse sorting
-n → Numerical sorting
-f → Case insensitive sorting
-r
-n
-f
👓 uniq: Omits repeated lines.
Following option can be used with uniq command:
-c→ Indicates the number of occurrences of a line.
☕️ tee: Reads from the standard input and writes to both standard output and one or more files at the same time.
The above command creates newfile1.txt and newfile2.txt with the text “New text here”.
Following option can be used with tee command:
-a→ Appends the output to a file instead of overwriting it.
Use /dev/null to hide the standard output
✂️ cucut: Slices a line and extracts the text. It is necessary to specify option with command otherwise it gives error.
Following options can be used with cut command
-b → Extracts specific bytes
-c → Cuts the characters by column
-f → Cuts the character to the delimiter character with the specified field number
-d → delimiter, mostly used in conjunction with -f
Filter the text to get 1st, 4th & 8th character using -b
Filter the text to get characters in range [1–4] & [9–11] using -b
Filter text to get characters in column [1–3] using -c
Filter text to get last name using -d
✏️ fmt: A Simple optimal text formatter, it reformats paragraphs in specified file.
Following option can be used with fmt command:
-w → Reformat the text with a specific line width
...
🤯 head: Displays the first parts of a file, it outputs the first 10 lines by default.
$ cat sample.txt | headAdriaens DishmanAnna TichnerBank GuerroPhil CuniamReagen DobrovolnyCicily VealeCoop Joyseykendrick Liggonsmicheal Fraybenn Cork
Following option can be used with head command:
-n → Number of lines to be displayed
$ cat sample.txt | head -n 5Adriaens DishmanAnna TichnerBank GuerroPhil CuniamReagen Dobrovolny
🌀 tail: Displays the last parts of a file, it outputs the last 10 lines by default.
$ cat sample.txt | tailAnna TichnerBank GuerroPhil CuniamReagen DobrovolnyCicily VealeCoop Joyseykendrick Liggonsmicheal Fraybenn CorkMicheal Fray
Following option can be used with tailcommand:
-n → Number of lines to be displayed
$ cat sample.txt | tail -n 5Coop Joyseykendrick Liggonsmicheal Fraybenn CorkMicheal Fray
📝 tr: Translates or deletes characters from standard input.
Lowercase to uppercase
$ cat sample.txt | tr [:lower:] [:upper:]ADRIAENS DISHMANANNA TICHNERBANK GUERROPHIL CUNIAMREAGEN DOBROVOLNYCICILY VEALECOOP JOYSEYKENDRICK LIGGONSMICHEAL FRAYBENN CORKMICHEAL FRAY
Note: We can also use regular expressions to translate the data.
Apply ROT13 cipher to translate the data. To know more about ROT13 visit here.
$ cat sample.txt | tr a-zA-Z n-za-mN-ZA-MNqevnraf QvfuznaNaan GvpuareOnax ThreebCuvy PhavnzErntra QboebibyalPvpvyl IrnyrPbbc Wblfrlxraqevpx Yvttbafzvpurny Senloraa PbexZvpurny Senl
⏳ sed: A stream editor for filtering and transforming text.
We can use regular expressions to transform our text.
To replace a substring: ‘s/text to replace/replacement text
$ cat sample.txt | sed 's/micheal/Michelle/'Adriaens DishmanAnna TichnerBank GuerroPhil CuniamReagen DobrovolnyCicily VealeCoop Joyseykendrick LiggonsMichelle Fraybenn CorkMicheal Fray
To replace the nth occurrence: ‘s/text to replace/replacement text/occurence_no
$ cat sample.txt | sed 's/Micheal/Michelle/1'Adriaens DishmanAnna TichnerBank GuerroPhil CuniamReagen DobrovolnyCicily VealeCoop Joyseykendrick Liggonsmicheal Fraybenn CorkMichelle Fray
To replace all occurrences: ‘s/text to replace/replacement text/g
$ cat sample.txt |tr [:upper:] [:lower:] |sed 's/micheal/michelle/g'adriaens dishmananna tichnerbank guerrophil cuniamreagen dobrovolnycicily vealecoop joyseykendrick liggonsmichelle fraybenn corkmichelle fray
To delete a line: ‘(line num)d’
For nth line replace ‘2’ with the number of your line
$ cat sample.txt | sed '2d'Adriaens DishmanBank GuerroPhil CuniamReagen DobrovolnyCicily VealeCoop Joyseykendrick Liggonsmicheal Fraybenn CorkMicheal Fray
To delete lines from range x to y: ‘(first line), (last line)d’
$ cat sample.txt | sed '1,5d'Cicily VealeCoop Joyseykendrick Liggonsmicheal Fraybenn CorkMicheal Fray
To delete last line: ‘$d’
$ cat sample.txt | sed '$d'Adriaens DishmanAnna TichnerBank GuerroPhil CuniamReagen DobrovolnyCicily VealeCoop Joyseykendrick Liggonsmicheal Fraybenn Cork
To delete a line that matches a pattern: ‘pattern’
$ cat sample.txt | sed '/A/d'Bank GuerroPhil CuniamReagen DobrovolnyCicily VealeCoop Joyseykendrick Liggonsmicheal Fraybenn CorkMicheal Fray
✍️ od: Returns contents of a file in specified number system. It returns hexadecimal by default.
$ cat sample.txt | od0000000 062101 064562 062541 071556 042040 071551 066550 0671410000020 005015 067101 060556 052040 061551 067150 071145 0050150000040 060502 065556 043440 062565 071162 005157 064120 0661510000060 041440 067165 060551 006555 051012 060545 062547 0201560000100 067504 071142 073157 066157 074556 005015 064503 0645430000120 074554 053040 060545 062554 005015 067503 070157 0450400000140 074557 062563 006571 065412 067145 071144 061551 0201530000160 064514 063547 067157 006563 066412 061551 062550 0661410000200 043040 060562 006571 061012 067145 020156 067503 0655620000220 005015 064515 064143 060545 020154 071106 074541 0050150000240
Get output in octal using -b
$ cat sample.txt | od -b0000000 101 144 162 151 141 145 156 163 040 104 151 163 150 155 ... 0000020 015 012 101 156 156 141 040 124 151 143 150 156 145 162 ...0000040 102 141 156 153 040 107 165 145 162 162 157 012 120 150 ...0000060 040 103 165 156 151 141 155 015 012 122 145 141 147 145 ...0000100 104 157 142 162 157 166 157 154 156 171 015 012 103 151 ...0000120 154 171 040 126 145 141 154 145 015 012 103 157 157 160 ...0000140 157 171 163 145 171 015 012 153 145 156 144 162 151 143 ...0000160 114 151 147 147 157 156 163 015 012 155 151 143 150 145 ...0000200 040 106 162 141 171 015 012 142 145 156 156 040 103 157 ...0000220 015 012 115 151 143 150 145 141 154 040 106 162 141 171 ...
Get output in character format using -c
$ cat sample.txt | od -c0000000 A d r i a e n s D i s h m a n0000020 \r \n A n n a T i c h n e r \r \n0000040 B a n k G u e r r o \n P h i l0000060 C u n i a m \r \n R e a g e n0000100 D o b r o v o l n y \r \n C i c i0000120 l y V e a l e \r \n C o o p J0000140 o y s e y \r \n k e n d r i c k0000160 L i g g o n s \r \n m i c h e a l0000200 F r a y \r \n b e n n C o r k0000220 \r \n M i c h e a l F r a y \r \n0000240
✣ wc: Returns line, word and character count.
$ cat sample.txt | wc11 22 160
Hope you are now better at understanding pipes and filters!
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