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Notice that the first ">" is numbered while the second is not. This is because standard output is flow 1 and the ">" redirect presumes flow 1 if no number is provided. It is important to know what resources of data your shell could divert, to understand the joys of redirection. It is composed of instructions or the information submitted to the shell for analysis. Most of the moment, this comes in the user typing things. Rather, we could use the "<" to redirect sorted variations of each file in to "comm", that would seem like that: No find / -name wireless &> results.txt $ find / -name wireless 2> denied.txt > found.txt For instance, what if you wished to search your entire system for wireless interface information that is accessible to non-root users? For this, we can employ the powerful "find" command. Redirecting Standard Error These building blocks are enough to allow possibilities that are infinite, although this is just a basic summary of redirection from the shell functions. Like everything else about the terminal, However, the best way to get a taste of the things it can do is to try it out for yourself 3 Streams It's the flow of data after doing some process, usually that the shell outputs as you would imagine. What if you wanted to conserve the results to their own record? Since streams can be redirected we can just put in our output redirection towards our command's finish like this: Ultimately, in Case You wanted all the info from this command -- mistakes and successful finds -- hauled in the same place, you can redirect both streams to the Identical place using "&>" as follows: We can divert the flow of mistake to do things such as make error log files, or mistakes and returned data. This isn't terribly useful, but we can build it on by implementing an additional measure. Let's say you are trying to track the route your traffic takes on the Internet changes from day to day. Even the "traceroute" command will tell us every router, including the infrastructural ones in the back of the Internet, that our link travels through from origin to destination, the latter being a URL given as an argument. Much like parentheses in math, with what is left the shell processes orders in parentheses first and then proceeds. The two documents are sorted and then fed into "comm", which then compares them and presents the results. $ date > date.txt Let us say you need to create a file that lists the time and date of today. Luckily for us, there is a control that returns that information, aptly called "date". Commands usually return the info they process to the standard output of shell. To get it into a file, we insert ">" after the command and before the title of the destination document (using a space on each side). Normally, when a content (More Bonuses) non-root user runs "find" system-wide, it elevates standard output and standard error to the terminal, however there is generally more of this latter than before, making it tough to find out the desired information. We can solve this by simply redirecting standard error to a file using "2>" (since standard error is flow 2), and this leaves only normal output returned to the terminal window: With redirection, whatever file is specified after the ">" is overwritten, so unless you're sure that you won't drop anything significant, it is best to give a brand new name, in which event a file with that name will be created. Let's call it "date.txt" (that the file extension following the period usually is not important, but assists us people with business). $ find / -name wireless 2> denied.txt We all need to do is change the title of the file to something more descriptive, with the "mv" command using its original name as the primary argument and the new name since the next, like so: Redirecting Standard Output The final stream, "standard error," numbered flow 2, is similar to standard output as it generally takes the kind of information thrown into the terminal window. However, it is different from regular output so that the flows can be handled if desired. This can be helpful when you have a command working on lots of data in a complex, error-prone operation, and you do not need the data and errors produced to have dumped in precisely the exact same file. As we already have a document with a date in it, it'd be sensible just to tack onto the data from our scanning into the end of that record ("date.txt"). To do this, we just use two ">" characters next to each other (">>"). Our brand new redirection looks like this: Redirection entails redirecting them and carrying these streams as you have probably guessed. This can be accomplished with the ">" and "<" characters in a variety of combinations, depending on the place you need your information to end up. For your shell, the control interpreter of the terminal, these symbols aren't wasted keys -- they operators who could link information together, split it. One of the easiest and shell operations is redirection. By using a "<" instead of ">", we can redirect standard input signal by simply replacing a document for this. $ comm <(kind list1.txt) <(sort list2.txt) There's a "sort" command, however although it is going to return a sorted list to the terminal, and it won't permanently sort the listing, which sets us back in square one. We might rescue the sorted version of each listing to its own file with ">" and then run "comm", yet this approach would require two commands once we could reach the same thing with a single (and with no leftover files). If you have taken the opportunity you're probably at the point in which you wish to begin putting what you have learned. Sometimes issuing one at a time is enough, however there are cases when it may be tedious to enter command after control to perform a simple job. The place where the symbols on your keyboard come in this is. Let us say you have two documents, "list1.txt" along with "list2.txt", which each contain an unsorted list. There's some overlap while every listing includes things the other doesn't. We can discover the traces which are in common with the "comm" command, however, only as long as the lists have been sorted.