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Finally, we could divert the stream of regular mistake to do things such as make error log files, or errors and returned data. $ comm <(kind list1.txt) <(sort list2.txt) It's important to know what sources of data your shell may redirect, to understand the workings of redirection. The initial would be "standard input," numbered by your system as flow 0 (because computers count from 0). It consists of the advice or instructions submitted into the shell for evaluation. Most of the moment, this stems in the user typing things. Rather, we could use the "<" to divert sorted variations of each file to "comm", that would look like that: Let us say you would like to create a document that lists time and the current date. Fortunately for us, there's a command that returns that advice, aptly called "date". The info that that they procedure to the standard output of shell is usually returned by commands. To receive it in a document, we insert ">" after the command and before the name of the destination document (using a space on each side). Notice that the initial ">" is numbered while the next isn't. That is because standard output is stream 1 and the ">" redirect assumes flow 1 if no number is given. By employing a "<" instead of ">", we can redirect standard input signal by simply substituting a document for it. As with parentheses in math, with what is left the shell processes orders in parentheses first and then proceeds. The 2 documents are sorted and then fed to "comm", which then contrasts them and presents the results. You are probably at the point in which you would like to start putting what you have learned, if you have taken the opportunity to get the website - explanation - hang of terminal basics. There are instances when it can be tedious to put in command after control to carry out a simple undertaking, although sometimes issuing one at a time is sufficient. Where the extra symbols on your computer come in this is. Ultimately, if you wanted All of the information from this command -- errors and successful finds -- hauled in Exactly the Same place, you could redirect both flows to the same place using "&>" as follows: For instance, what if you wished to search your whole system interface information that is accessible to consumers? For this, we could use the powerful "find" command. As you have probably figured, redirection entails carrying these flows and redirecting them. These building blocks are sufficient to allow possibilities that are infinite, although this is just a basic overview of how redirection from the shell functions. Like anything else about the terminal the best way to get a taste of what it can do is to try it out for yourself $ date > date.txt With redirection, whatever file is given following the ">" is overwritten, so unless you're sure you won't eliminate anything significant, it is best to provide a brand new name, in which event a file with that name will be created. Let's call it "date.txt" (the file extension following the period typically is not important, but assists us people with organization). The next, "standard output," is numbered as flow 1. As you could imagine, it's the flow of data that the shell sparks after doing some procedure, usually. Since we already have a record using a date inside, it'd be sensible only to tack on the data from our scanning to the end of the record ("date.txt"). Redirecting Standard Output For your shell, the command interpreter of the terminal, those symbols are not wasted keys -- they are strong operators that could link information together, divide it. One of the easiest and most effective shell surgeries is redirection. Now all we need to do is to change the title of the document into something more descriptive, with the "mv" command with its original name as the first argument and the new name because the next, like this: This is useful, but we can build it on by executing an additional measure. Let's say you are trying to track the route your traffic takes over the Internet changes from day to day. The "traceroute" command will inform us each router, including the infrastructural ones in the back of the Internet, that our connection travels through from origin to destination, and the latter being a URL provided as an argument. There is a "sort" command, but even though it will return a sorted listing to the terminal, and it will not permanently form the list, which places us back at square one. We could rescue the sorted version of each set to its own document with ">" and then run "comm", yet this approach will require two controls once we could achieve the identical thing with you (and without leftover files). Ordinarily, when a non-root user conducts "find" system-wide, it elevates standard output and standard error to the terminal, but there is usually more of this latter than before, making it tough to pick out the desired data. We can fix this Simply by redirecting standard error to a file using "2>" (since normal error is flow 2), which renders just normal output returned to the terminal window: Redirecting Standard Error No find / -name wireless &> results.txt What if you wished to conserve the valid results to their own file? Since streams can be redirected individually, we can put in our Typical output redirection towards our command's finish like this: 3 Streams The last stream, "standard error," numbered stream 2, is very similar to standard output in that it normally takes the form of data dumped into the terminal window. However, it is conceptually different from output if desired, so that the streams can be managed. This can be helpful when you've got a command working on lots of information in a complex, error-prone operation, and you also do not want errors and the data produced to have chucked in the file. Let us say you have two documents, "list1.txt" and also "list2.txt", which each comprise an unsorted list. There is some overlap while every list includes items the other does not. We can come across the lines which are in standard using the "comm" command, but only as long as the lists are sorted.