> ## Content Index > Fetch the complete content index at: https://snubmonkey.com/llms.txt > Use this file to discover other available public pages before exploring further. # Working with pipes || on Linux. - URL: https://snubmonkey.com/working-with-pipes-on-the-linux-command-line/ - Published: 2021-09-24T06:03:00.000Z - Updated: 2025-04-16T22:38:19.000Z - Description: No, no, nooo... not the PVC one!!! ... but this command-line pipe is just as useful, and its hold a ton of value for system administrators. The | command is called a pipe. It's a form of redirection in Linux used to connect the STDOUT of one command into the STDIN of a second command. - Author: Aleksandra Sloan - Tags: how to 🪄, linux 🐧 It is used to pipe, or transfer, the standard output from the command on its left into the standard input of the command on its right. Plus, you can stack piped commands as many times as you want, or until you run out of output or file descriptors. Filtering is one of the primary functions of piping. You use piping to filter the contents of a large file, for example, to find a specific string or word. Let's look at some real-world examples of how piping works. ## Counting files in a given directory The easiest way to count files in a directory on Linux is to use the `ls` command and pipe it with the `wc -l` command. ```zsh $ ls | wc -l ``` The **`wc`** command is used on Linux in order to print the bytes, characters or newlines count. However, in this case, we are using this command to count the number of files in a directory. For instance; let’s say that you want **to count the number of files** present in the "/etc" directory. Well will run `ls` command on the "/etc" directory and pipe it into the `wc` command. ```zsh $ ls /etc | wc -l or $ ls -1 /etc |wc -l -1 list one file per line OUPUT 211 ``` ## Remarks When using the `wc` command, an important thing to remember is that it counts the number of newlines for a given command. As a result, there is a significant difference between those two commands. ```zsh $ ls /etc | wc -l 211 $ ls -l /etc |wc -l 212 ``` As a consequence, you are counting a line that should not be counted, incrementing the final result by one. *ps*: ***why does `ls -l` count more files than I do?*** ```zsh $ ls -l total 1116 ``` The `1116` you see here is **not the number of files**. Indeed, t**he number of disk blocks consumed**. ## Count Files Recursively using `find` In order to count files recursively on Linux, you have to use both the `find` and `wc` commands; all will be passed through the `|` command in order to count the number of files. *E.g.* if you want to recursively count unhidden/hidden files in the "/etc" directory. ``` $ sudo find /etc -type f | wc -l 2054 HIDDEN $ sudo find /etc -name ".*" | wc -l 14 or $ sudo find /etc -type f -name ".*" | wc -l 14 ``` The **`find`** command, by default, does not stop at the first depth of the directory: it will explore every single subdirectory, making the file search recursive. Note the **`f`** option, as we are **targeting** only **files**. Below, we will count each and every directory followed by any hidden one in the "/etc" directory. ```zsh $ sudo find /etc -type d | wc -l 370 $sudo find /etc -type d -name ".*" | wc -l 0 ``` Note the `**-type** **d**` option, as we are **targeting** only **directories**. ## Fetch particular data with pipes In this example, we only display the available space on a file system. ```zsh $ df -h Filesystem Size Used Avail Use% Mounted on udev 889M 0 889M 0% /dev tmpfs 600M 4.0M 597M 1% /run /dev/mmcblk0p2 129G 11G 118G 17% / tmpfs 935M 0 935M 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 935M 0 935M 0% /sys/fs/cgroup /dev/loop1 85M 85M 0 100% /snap/core/11321 /dev/loop2 46M 46M 0 100% /snap/core18/1948 /dev/loop0 85M 85M 0 100% /snap/core/11425 /dev/loop4 27M 27M 0 100% /snap/snapd/12705 /dev/loop3 46M 46M 0 100% /snap/core18/2072 /dev/loop5 53M 53M 0 100% /snap/lxd/21031 /dev/loop6 27M 27M 0 100% /snap/snapd/12396 /dev/loop7 51M 51M 0 100% /snap/lxd/20329 /dev/sda 30G 11G 18G 37% /mnt/SRYUJHIU76883 ``` The **`df`** command (short for disk free), is used to display information related to file systems about total space and available space. The **`-h`** option stands for **human-readable** and itprints sizes in the power of 1024*.* Now, we will use the `|` command **to highlight** only the lines that do contain the character '**G**' for Gigabit and the word '**Filesystem**' ```zsh $ df -h | grep -E 'G|Filesystem' Filesystem Size Used Avail Use% Mounted on /dev/mmcblk0p2 129G 11G 118G 17% / /dev/sda 30G 11G 18G 37% /mnt/SRYUJHIU76883 ``` The **`grep`** command searches for patterns in each file. The **`-E`** option helps to search content by applying extended regular expressions to display the machining lines. ## Use multiple pipes in a single command In this example, unlike the earlier ones, we will be using more than one `|` in a single command to elaborate its functionality. We have a file named fire.txt that contains ***14344418*** lines. ```zsh $ cat fire.txt | wc -l 14344418 ``` Now, we want to get the record of the occurrence of the word that matches the name we have provided in the command. The **`cat`** (short for "**concatenate**") command is used to fetch data from a particular file. The **`sort`** command is used to sort a file, arranging the records in a particular order. `-r` option tells to **sort in random order**. The **`uniq`** command filters out the repeated lines in a file. The **`tee`** command reads from the standard input and writes to both standard output and one or more files at the same time. It is mostly used in combination with other commands through piping. Basically, it is used to save the result in another file, here named fire-2.txt ```zsh $ cat fire.txt | grep monkey | sort -r | uniq | tee fire-2.txt | wc -l 6723 ``` As you can see the word monkey is occurring **6723** times. Let's double-check or say! ```zsh $ du -sch * | grep fire 80K fire-2.txt 134M fire.txt ``` The file fire-2.txt has been created and its size has dramatically shrunken from 134M to 80K, keeping the non-duplicates. Now, let's see its content. ```zsh $ cat fire-2.txt ... jomonkey39 monkey130 lil.monkey monkeyhands codemonkey19 frozenmonkey monkey1740 monkey1990 fnkymonkey monkeys083 doublejandmonkey ... ``` Thank you for reading. As we saw, the `|` command helps us mashed-up two or more commands at the same time and run them consecutively; basically, passes a parameter such as the output of one process to another process that accepts it as input. The possibilities here are just limited by your imagination.