- #Mac command line list contents of directory mac os x
- #Mac command line list contents of directory code
Try using pipes and backticks on your own to see the differences after all, doing is the best way to learn.Ī few other ways to combine commands exist. If this seems slightly confusing at first, don't worry. Thus, the backticks give you the line count for each non-hidden item in your home directory, whereas the pipe builds a command that tells you how many non-hidden items there are in the home directory. The pipe, on the other hand, takes the output from ls and makes it as the standard input for the wc command. Using backticks will take the results of ls above and use them as the arguments for wc, thus: To show the difference between the pipe and the backtick, let's look at how we can combine the ls and wc commands.Īdam.txt Documents Movies Pictures Sites temp.html who_listĭesktop Library Music Public personal test_1.txt
For example, we've already seen the use of backticks, `, to expand the results of a command into another command. The pipe is only one way to put more than one command on one command line, because there are different ways that you might want to combine them. (I hit 'q' at this point to quit out of more.) So, what if we want to see all of the files, but not have them fly by at breakneck speed? Why, pipe the output through more (or page or less). That's a lot of files, far more than is standard for a Terminal.app console. First, using a pipe to connect commands, we can determine how many files exist in the directory: Recall from an earlier column that we took a quick look at the /usr/bin directory where a lot of commands reside. One of the more common uses of the pipe on the command line is to take a large amount of output and present it only one screen at a time using the more command (or page or less). (Actually, once they start they'll never shut up so don't ask, just take my word for it.)
#Mac command line list contents of directory code
Anyone who has ever written code to do this in a language like C can tell you how great the shell is at this. And what's more, it makes things very simple for you. Given the many options that Unix commands can have, and the number of Unix commands, this also gives you great flexibility. The beauty of this is that you can take very simple tools, string them together in whatever order you wish, and create complex tools. The Unix genius who wrote this wants me to take the output from the command on the left, who -Hu, and make it the input for the command on the right, tr a-z A-Z." So it does. What this does is that, when tcsh is parsing the command line behind the scenes, it sees the "|" character and says "What ho! A pipe.
dr_unix% who -Hu | tr a-z A-Z > Cap_who_list Recall the example from the previous column where we typed: dr_unix% command1 sourcefile | command2 | command3 | command4 > out_file We could have performed the previous task all in one line. In Unix shells, this is accomplished with a pipe, "|". Oh, a crusty old mainframer might hit you with a slide rule if you say this out loud, but think about it: all you need is a mechanism that will take the output from command1 and make it the standard input for command2, and so on. If you think about it, you really don't need those tempfiles. Not only do you have to spend a lot of time typing and waiting, but constant I/O to a drive is generally the worst drag on speed. Worse, you might erase the wrong file along the way. That is a lot of typing it discourages laziness and impatience. dr_unix% command1 sourcefile > tempfile1 However, what if you want to run several commands on your data? Well, you could do something like this: In the last column, we looked at how input and output can be redirected to and from files. If you have any questions about what you read here, check out the earlier columns, write back in the comments below, or join us in the Hardcore X! forum.
#Mac command line list contents of directory mac os x
This series is designed to help you learn more about the Mac OS X command line. "Tiny differences in input could quickly become overwhelming differences in output." The Mac Observer Express Daily Newsletter