3 [Back To The Setup](http://swcarpentry.github.com/boot-camps/2013-01-12-chicago/)
4 - [Forward to Python](https://github.com/thehackerwithin/boot-camps/tree/2013-01-chicago/python/intro)
8 **Updated and presented by : Radhika Khetani**
10 **Modified by : Sasha Wood**
12 **This presentation originally developed by: Milad Fatenejad**
14 # What is the shell how do I access the shell?
16 The *shell* is a program that presents a command line interface
17 which allows you to control your computer using commands entered
18 with a keyboard instead of controlling graphical user interfaces
19 (GUIs) with a mouse/keyboard combination.
21 Use the GUI to open the tutorial on github. Single click on the "Firefox
22 Web Browser". Type in the URL:
23 github.com/thehackerwithin/boot-camps/tree/2013-01-chicago
25 Click on the directory named `shell`.
27 A *terminal* is a program you run that gives you access to the
28 shell. There are many different terminal programs that vary across
31 There are many reasons to learn about the shell. In my opinion, the
32 most important reasons are that:
34 1. It is very common to encounter the shell and
35 command-line-interfaces in scientific computing, so you will
36 probably have to learn it eventually
38 2. The shell is a really powerful way of interacting with your
39 computer. GUIs and the shell are complementary - by knowing both
40 you will greatly expand the range of tasks you can accomplish with
41 your computer. You will also be able to perform many tasks more
44 The shell is just a program and there are many different shell
45 programs that have been developed. The most common shell (and the one
46 we will use) is called the Bourne-Again SHell (bash). Even if bash is
47 not the default shell, it is usually installed on most systems and can be
48 started by typing `bash` in the terminal. Many commands, especially a
49 lot of the basic ones, work across the various shells but many things
50 are different. I recommend sticking with bash and learning it well.
51 ([Here is a link for more information](http://en.wikipedia.org/wiki/Bash_(Unix_shell))
53 To open a terminal, just single click on the "Terminal" icon on the
56 # The Example: Manipulating Experimental Data Files
58 We will spend most of our time learning about the basics of the shell
59 by manipulating some experimental data from a hearing test. To get
60 the data for this test, you will need internet access. Just enter the
63 git clone https://github.com/thehackerwithin/boot-camps.git
68 git checkout 2013-01-chicago
70 These 2 commands will grab all of the data needed for this workshop from the
75 One very basic command is `echo`. This command just prints text to
76 the terminal. Try the command:
80 Then press enter. You should see the text "Hello, World" printed back
81 to you. The echo command is useful for printing from a shell script,
82 for displaying variables, and for generating known values to pass
85 ## Moving around the file system
87 Let's learn how to move around the file system using command line
88 programs. This is really easy to do using a GUI (just click on
89 things). Once you learn the basic commands, you'll see that it is
90 really easy to do in the shell too.
92 First we have to know where we are. The program `pwd` (print working
93 directory) tells you where you are sitting in the directory tree. The
94 command `ls` will list the files in files in the current
95 directory. Directories are often called "folders" because of how they
96 are represented in GUIs. Directories are just listings of files. They
97 can contain other files or directories.
99 Whenever you start up a terminal, you will start in a special
100 directory called the *home* directory. Every user has their own home
101 directory where they have full access to do whatever they want. In
102 this case, the `pwd` command tells us that we are in the `/home/swc`
103 directory. This is the home directory for the `swc` user. That is our
104 user name. You can always find out your user name by entering the
109 When you enter the `ls` command lists the contents of the current
110 directory. There are several items in the home directory, notice that
111 they are all colored blue. This tells us that all of these items are
112 directories as opposed to files.
114 Lets create an empty file using the `touch` command. Enter the
119 Then list the contents of the directory again. You should see that a
120 new entry, called `testfile`, exists. It is colored white meaning that
121 it is a file, as opposed to a directory. The `touch` command just
122 creates an empty file.
124 Some terminals will not color the directory entries in this very
125 convenient way. In those terminals, use `ls -F` instead of `ls`. The
126 `-F` argument modifies the results so that a slash is placed at the
127 end of directories. If the file is *executable* meaning that it can be
128 run like a program, then a star fill be placed of the file name.
130 You can also use the command `ls -l` to see whether items in a
131 directory are files or directories. `ls -l` gives a lot more
132 information too, such as the size of the file and information about
133 the owner. If the entry is a directory, then the first letter will be
134 a "d". The fifth column shows you the size of the entries in
135 bytes. Notice that `testfile` has a size of zero.
137 Now, let's get rid of `testfile`. To remove a file, just enter the
142 The `rm` command can be used to remove files. If you enter `ls` again,
143 you will see that `testfile` is gone.
146 **Changing Directories**
148 Now, let's move to a different directory. The command `cd` (change
149 directory) is used to move around. Let's move into the `boot-camps`
150 directory. Enter the following command:
154 Now use the `ls` command to see what is inside this directory. You
155 will see that there is an entry which is green. This means that this
156 is an executable. If you use `ls -F` you will see that this file ends
159 This directory contains all of the material for this boot camp. Now
160 move to the directory containing the data for the shell tutorial:
164 If you enter the `cd` command by itself, you will return to the home
165 directory. Try this, and then navigate back to the `shell`
170 Most programs take additional arguments that control their exact
171 behavior. For example, `-F` and `-l` are arguments to `ls`. The `ls`
172 program, like many programs, take a lot of arguments. But how do we
173 know what the options are to particular commands?
175 Most commonly used shell programs have a manual. You can access the
176 manual using the `man` program. Try entering:
180 This will open the manual page for `ls`. Use the space key to go
181 forward and b to go backwards. When you are done reading, just hit `q`
184 Programs that are run from the shell can get extremely complicated. To
185 see an example, open up the manual page for the `find` program,
186 which we will use later this session. No one can possibly learn all of
187 these arguments, of course. So you will probably find yourself
188 referring back to the manual page frequently.
190 **Examining the contents of other directories**
192 By default, the `ls` commands lists the contents of the working
193 directory (i.e. the directory you are in). You can always find the
194 directory you are in using the `pwd` command. However, you can also
195 give `ls` the names of other directories to view. Navigate to the
196 home directory if you are not already there. Then enter the
201 This will list the contents of the `boot-camps` directory without
202 you having to navigate there. Now enter:
206 This prints the contents of `shell`. The `cd` command works in a
207 similar way. Try entering:
211 and you will jump directly to `shell` without having to go through
212 the intermediate directory.
214 ## Full vs. Relative Paths
216 The `cd` command takes an argument which is the directory
217 name. Directories can be specified using either a *relative* path a
218 full *path*. The directories on the computer are arranged into a
219 hierarchy. The full path tells you where a directory is in that
220 hierarchy. Navigate to the home directory. Now, enter the `pwd`
221 command and you should see:
225 which is the full name of your home directory. This tells you that you
226 are in a directory called `swc`, which sits inside a directory called
227 `home` which sits inside the very top directory in the hierarchy. The
228 very top of the hierarchy is a directory called `/` which is usually
229 referred to as the *root directory*. So, to summarize: `swc` is a
230 directory in `home` which is a directory in `/`.
232 Now enter the following command:
234 cd /home/swc/boot-camps/shell
236 This jumps to `shell`. Now go back to the home directory. We saw
237 earlier that the command:
241 had the same effect - it took us to the `shell` directory. But,
242 instead of specifying the full path
243 (`/home/swc/boot-camps/shell`), we specified a *relative path*. In
244 other words, we specified the path relative to our current
245 directory. A full path always starts with a `/`. A relative path does
246 not. You can usually use either a full path or a relative path
247 depending on what is most convenient. If we are in the home directory,
248 it is more convenient to just enter the relative path since it
249 involves less typing.
251 Now, list the contents of the /bin directory. Do you see anything
255 ## Saving time with shortcuts, wild cards, and tab completion
259 There are some shortcuts which you should know about. Dealing with the
260 home directory is very common. So, in the shell the tilde character,
261 `~`, is a shortcut for your home directory. Navigate to the `shell`
262 directory, then enter the command:
266 This prints the contents of your home directory, without you having to
267 type the full path. The shortcut `..` always refers to the directory
268 above your current directory. Thus:
272 prints the contents of the `/home/swc/boot-camps`. You can chain
277 prints the contents of `/home/swsc` which is your home
278 directory. Finally, the special directory `.` always refers to your
279 current directory. So, `ls`, `ls .`, and `ls ././././.` all do the
280 same thing, they print the contents of the current directory. This may
281 seem like a useless shortcut right now, but we'll see when it is
282 needed in a little while.
284 To summarize, the commands `ls ~`, `ls ~/.`, `ls ../../`, and `ls
285 /home/swc` all do exactly the same thing. These shortcuts are not
286 necessary, they are provided for your convenience.
288 **Our data set: Cochlear Implants**
290 A cochlear implant is a small electronic device that is surgically
291 implanted in the inner ear to give deaf people a sense of
292 hearing. More than a quarter of a million people have them, but there
293 is still no widely-accepted benchmark to measure their effectiveness.
294 In order to establish a baseline for such a benchmark, our supervisor
295 got teenagers with CIs to listen to audio files on their computer and
298 1. the quietest sound they could hear
299 2. the lowest and highest tones they could hear
300 3. the narrowest range of frequencies they could discriminate
302 To participate, subjects attended our laboratory and one of our lab
303 techs played an audio sample, and recorded their data - when they
304 first heard the sound, or first heard a difference in the sound. Each
305 set of test results were written out to a text file, one set per file.
306 Each participant has a unique subject ID, and a made-up subject name.
307 Each experiment has a unique experiment ID. The experiment has
308 collected 351 files so far.
310 The data is a bit of a mess! There are inconsistent file names, there
311 are extraneous "NOTES" files that we'd like to get rid of, and the
312 data is spread across many directories. We are going to use shell
313 commands to get this data into shape. By the end we would like to:
315 1. Put all of the data into one directory called "alldata"
317 2. Have all of the data files in there, and ensure that every file
318 has a ".txt" extension
320 3. Get rid of the extraneous "NOTES" files
322 If we can get through this example in the available time, we will move
323 onto more advanced shell topics...
327 Navigate to the `~/boot-camps/shell/data/THOMAS` directory. This
328 directory contains our hearing test data for THOMAS. If we type `ls`,
329 we will see that there are a bunch of files which are just four digit
330 numbers. By default, `ls` lists all of the files in a given
331 directory. The `*` character is a shortcut for "everything". Thus, if
332 you enter `ls *`, you will see all of the contents of a given
333 directory. Now try this command:
337 This lists every file that ends with a `1`. This command:
341 Lists every file in `/usr/bin` that ends in the characters `.sh`. And
346 lists every file in the current directory which contains the number
347 `4`, and ends with the number `1`. There are four such files: `0241`,
348 `0341`, `0431`, and `0481`.
350 So how does this actually work? Well...when the shell (bash) sees a
351 word that contains the `*` character, it automatically looks for files
352 that match the given pattern. In this case, it identified four such
353 files. Then, it replaced the `*4*1` with the list of files, separated
354 by spaces. In other the two commands:
357 ls 0241 0341 0431 0481
359 are exactly identical. The `ls` command cannot tell the difference
360 between these two things.
365 Do each of the following using a single `ls` command without
366 navigating to a different directory.
368 1. List all of the files in `/bin` that contain the letter `a`
369 2. List all of the files in `/bin` that contain the letter `a` or the letter `b`
370 3. List all of the files in `/bin` that contain the letter `a` AND the letter `b`
376 Navigate to the home directory. Typing out directory names can waste a
377 lot of time. When you start typing out the name of a directory, then
378 hit the tab key, the shell will try to fill in the rest of the
379 directory name. For example, enter:
383 The shell will fill in the rest of the directory name for
384 `boot-camps`. Now enter:
388 When you hit the first tab, nothing happens. The reason is that there
389 are multiple directories in the home directory which start with
390 3. Thus, the shell does not know which one to fill in. When you hit
391 tab again, the shell will list the possible choices.
393 Tab completion can also fill in the names of programs. For example,
394 enter `e<tab><tab>`. You will see the name of every program that
395 starts with an `e`. One of those is `echo`. If you enter `ec<tab>` you
396 will see that tab completion works.
400 You can easily access previous commands. Hit the up arrow.
401 Hit it again. You can step backwards through your command history.
402 The down arrow takes your forwards in the command history.
404 ^-C will cancel the command you are writing, and give you a fresh prompt.
406 ^-R will do a reverse-search through your command history. This
411 Commands like `ls`, `rm`, `echo`, and `cd` are just ordinary programs
412 on the computer. A program is just a file that you can *execute*. The
413 program `which` tells you the location of a particular program. For
418 Will return "/bin/ls". Thus, we can see that `ls` is a program that
419 sits inside of the `/bin` directory. Now enter:
423 You will see that `find` is a program that sits inside of the
424 `/usr/bin` directory.
426 So ... when we enter a program name, like `ls`, and hit enter, how
427 does the shell know where to look for that program? How does it know
428 to run `/bin/ls` when we enter `ls`. The answer is that when we enter
429 a program name and hit enter, there are a few standard places that the
430 shell automatically looks. If it can't find the program in any of
431 those places, it will print an error saying "command not found". Enter
436 This will print out the value of the `PATH` environment variable. More
437 on environment variables later. Notice that a list of directories,
438 separated by colon characters, is listed. These are the places the
439 shell looks for programs to run. If your program is not in this list,
440 then an error is printed. The shell ONLY checks in the places listed
441 in the `PATH` environment variable.
443 Navigate to the `shell` directory and list the contents. You will
444 notice that there is a program (executable file) called `hello` in
445 this directory. Now, try to run the program by entering:
449 You should get an error saying that hello cannot be found. That is
450 because the directory `/home/swc/boot-camps/shell` is not in the
451 `PATH`. You can run the `hello` program by entering:
455 Remember that `.` is a shortcut for the current working
456 directory. This tells the shell to run the `hello` program which is
457 located right here. So, you can run any program by entering the path
458 to that program. You can run `hello` equally well by specifying:
460 /home/swc/boot-camps/shell/hello
466 When there are no `/` characters, the shell assumes you want to look
467 in one of the default places for the program.
472 We now know how to switch directories, run programs, and look at the
473 contents of directories, but how do we look at the contents of files?
475 The easiest way to examine a file is to just print out all of the
476 contents using the program `cat`. Enter the following command:
480 This prints out the contents of the `ex_data.txt` file. If you enter:
482 cat ex_data.txt ex_data.txt
484 It will print out the contents of `ex_data.txt` twice. `cat` just
485 takes a list of file names and writes them out one after another (this
486 is where the name comes from, `cat` is short for concatenate).
491 1. Print out the contents of the `~/boot-camps/shell/dictionary.txt`
492 file. What does this file contain?
494 2. Without changing directories, (you should still be in `shell`),
495 use one short command to print the contents of all of the files in
496 the `/home/swc/boot-camps/shell/data/THOMAS` directory.
500 `cat` is a terrific program, but when the file is really big, it can
501 be annoying to use. The program, `less`, is useful for this
502 case. Enter the following command:
504 less ~/boot-camps/shell/dictionary.txt
506 `less` opens the file, and lets you navigate through it. The commands
507 are identical to the `man` program. Use "space" to go forward and hit
508 the "b" key to go backwards. The "g" key goes to the beginning of the
509 file and "G" goes to the end. Finally, hit "q" to quit.
511 `less` also gives you a way of searching through files. Just hit the
512 "/" key to begin a search. Enter the name of the word you would like
513 to search for and hit enter. It will jump to the next location where
514 that word is found. Try searching the `dictionary.txt` file for the
515 word "cat". If you hit "/" then "enter", `less` will just repeat
516 the previous search. `less` searches from the current location and
517 works its way forward. If you are at the end of the file and search
518 for the word "cat", `less` will not find it. You need to go to the
519 beginning of the file and search.
521 Remember, the `man` program uses the same commands, so you can search
522 documentation using "/" as well!
527 Use the commands we've learned so far to figure out how to search
528 in reverse while using `less`.
535 Let's turn to the experimental data from the hearing tests that we
536 began with. This data is located in the `~/boot-camps/shell/data`
537 directory. Each subdirectory corresponds to a particular participant
538 in the study. Navigate to the `Bert` subdirectory in `data`. There
539 are a bunch of text files which contain experimental data
540 results. Lets print them all:
544 Now enter the following command:
546 cat au* > ../all_data
548 This tells the shell to take the output from the `cat au*` command and
549 dump it into a new file called `../all_data`. To verify that this
550 worked, examine the `all_data` file. If `all_data` had already
551 existed, we would overwritten it. So the `>` character tells the shell
552 to take the output from what ever is on the left and dump it into the
553 file on the right. The `>>` characters do almost the same thing,
554 except that they will append the output to the file if it already
560 Use `>>`, to append the contents of all of the files which contain the
561 number 4 in the directory:
563 /home/swc/boot-camps/shell/data/gerdal
565 to the existing `all_data` file. Thus, when you are done `all_data`
566 should contain all of the experiment data from Bert and any
567 experimental data file from gerdal that contains the number 4.
572 ## Creating, moving, copying, and removing
574 We've created a file called `all_data` using the redirection operator
575 `>`. This is critical file so we have to make copies so that the data
576 is backed up. Lets copy the file using the `cp` command. The `cp`
577 command backs up the file. Navigate to the `data` directory and enter:
579 cp all_data all_data_backup
581 Now `all_data_backup` has been created as a copy of `all_data`. We can
582 move files around using the command `mv`. Enter this command:
584 mv all_data_backup /tmp/
586 This moves `all_data_backup` into the directory `/tmp`. The directory
587 `/tmp` is a special directory that all users can write to. It is a
588 temporary place for storing files. Data stored in `/tmp` is
589 automatically deleted when the computer shuts down.
591 The `mv` command is also how you rename files. Since this file is so
592 important, let's rename it:
594 mv all_data all_data_IMPORTANT
596 Now the file name has been changed to all_data_IMPORTANT. Let's delete
599 rm /tmp/all_data_backup
601 The `mkdir` command is used to create a directory. Just enter `mkdir`
602 followed by a space, then the directory name.
609 1. Rename the `all_data_IMPORTANT` file to `all_data`.
610 2. Create a directory in the `data` directory called `foo`
611 3. Then, copy the `all_data` file into `foo`
615 By default, `rm`, will NOT delete directories. You can tell `rm` to
616 delete a directory using the `-r` option. Enter the following command:
623 The `wc` program (word count) counts the number of lines, words, and
624 characters in one or more files. Make sure you are in the `data`
625 directory, then enter the following command:
629 For each of the files indicated, `wc` has printed a line with three
630 numbers. The first is the number of lines in that file. The second is
631 the number of words. Finally, the total number of characters is
632 indicated. The final line contains this information summed over all of
633 the files. Thus, there were 10445 characters in total.
635 Remember that the `Bert/*` and `gerdal/*4*` files were merged
636 into the `all_data` file. So, we should see that `all_data` contains
637 the same number of characters:
641 Every character in the file takes up one byte of disk space. Thus, the
642 size of the file in bytes should also be 10445. Let's confirm this:
646 Remember that `ls -l` prints out detailed information about a file and
647 that the fifth column is the size of the file in bytes.
652 Figure out how to get `wc` to print the length of the longest line in
657 ## The awesome power of the Pipe
659 Suppose I wanted to only see the total number of character, words, and
660 lines across the files `Bert/*` and `gerdal/*4*`. I don't want to
661 see the individual counts, just the total. Of course, I could just do:
665 Since this file is a concatenation of the smaller files. Sure, this
666 works, but I had to create the `all_data` file to do this. Thus, I
667 have wasted a precious 7062 bytes of hard disk space. We can do this
668 *without* creating a temporary file, but first I have to show you two
669 more commands: `head` and `tail`. These commands print the first few,
670 or last few, lines of a file, respectively. Try them out on
676 The `-n` option to either of these commands can be used to print the
677 first or last `n` lines of a file. To print the first/last line of the
683 Let's turn back to the problem of printing only the total number of
684 lines in a set of files without creating any temporary files. To do
685 this, we want to tell the shell to take the output of the `wc Bert/*
686 gerdal/*4*` and send it into the `tail -n 1` command. The `|`
687 character (called pipe) is used for this purpose. Enter the following
690 wc Bert/* gerdal/Data0559 | tail -n 1
692 This will print only the total number of lines, characters, and words
693 across all of these files. What is happening here? Well, `tail`, like
694 many command line programs will read from the *standard input* when it
695 is not given any files to operate on. In this case, it will just sit
696 there waiting for input. That input can come from the user's keyboard
697 *or from another program*. Try this:
701 Notice that your cursor just sits there blinking. Tail is waiting for
702 data to come in. Now type:
709 then CONTROL+d. You should is the lines:
714 printed back at you. The CONTROL+d keyboard shortcut inserts an
715 *end-of-file* character. It is sort of the standard way of telling the
716 program "I'm done entering data". The `|` character is replaces the
717 data from the keyboard with data from another command. You can string
718 all sorts of commands together using the pipe.
720 The philosophy behind these command line programs is that none of them
721 really do anything all that impressive. BUT when you start chaining
722 them together, you can do some really powerful things really
723 efficiently. If you want to be proficient at using the shell, you must
724 learn to become proficient with the pipe and redirection operators:
728 **A sorting example**
730 Let's create a file with some words to sort for the next example. We
731 want to create a file which contains the following names:
738 To do this, we need a program which allows us to create text
739 files. There are many such programs, the easiest one which is
740 installed on almost all systems is called `nano`. Navigate to `/tmp`
741 and enter the following command:
745 Now enter the four names as shown above. When you are done, press
746 CONTROL+O to write out the file. Press enter to use the file name
747 `toBeSorted`. Then press CONTROL+x to exit `nano`.
749 When you are back to the command line, enter the command:
753 Notice that the names are now printed in alphabetical order.
758 Use the `echo` command and the append operator, `>>`, to append your
759 name to the file, then sort it and make a new file called Sorted.
763 Let's navigate back to `~/boot-camps/shell/data`. Enter the following command:
765 wc Bert/* | sort -k 3 -n
767 We are already familiar with what the first of these two commands
768 does: it creates a list containing the number of characters, words,
769 and lines in each file in the `Bert` directory. This list is then
770 piped into the `sort` command, so that it can be sorted. Notice there
771 are two options given to sort:
773 1. `-k 3`: Sort based on the third column
774 2. `-n`: Sort in numerical order as opposed to alphabetical order
776 Notice that the files are sorted by the number of characters.
781 Use the `man` command to find out how to sort the output from `wc` in
789 Combine the `wc`, `sort`, `head` and `tail` commands so that only the
790 `wc` information for the largest file is listed
792 Hint: To print the smallest file, use:
794 wc Bert/* | sort -k 3 -n | head -n 1
798 Printing the smallest file seems pretty useful. We don't want to type
799 out that long command often. Let's create a simple script, a simple
800 program, to run this command. The program will look at all of the
801 files in the current directory and print the information about the
802 smallest one. Let's call the script `smallest`. We'll use `nano` to
803 create this file. Navigate to the `data` directory, then:
807 Then enter the following text:
810 wc * | sort -k 3 -n | head -n 1
812 Now, `cd` into the `Bert` directory and enter the command
813 `../smallest`. Notice that it says permission denied. This happens
814 because we haven't told the shell that this is an executable
815 file. If you do `ls -l ../smallest`, it will show you the permissions on
816 the left of the listing.
818 Enter the following commands:
820 chmod a+x ../smallest
823 The `chmod` command is used to modify the permissions of a file. This
824 particular command modifies the file `../smallest` by giving all users
825 (notice the `a`) permission to execute (notice the `x`) the file. If
830 You will see that the file name is green and the permissions have changed.
831 Congratulations, you just created your first shell script!
835 You can search the contents of a file using the command `grep`. The
836 `grep` program is very powerful and useful especially when combined
837 with other commands by using the pipe. Navigate to the `Bert`
838 directory. Every data file in this directory has a line which says
839 "Range". The range represents the smallest frequency range that can be
840 discriminated. Lets list all of the ranges from the tests that Bert
848 Create an executable script called `smallestrange` in the `data`
849 directory, that is similar to the `smallest` script, but prints the
850 file containing the file with the smallest Range. Use the commands
851 `grep`, `sort`, and `tail` to do this.
858 The `find` program can be used to find files based on arbitrary
859 criteria. Navigate to the `data` directory and enter the following
864 This prints the name of every file or directory, recursively, starting
865 from the current directory. Let's exclude all of the directories:
867 find . -type f -print
869 This tells `find` to locate only files. Now try these commands:
871 find . -type f -name "*1*"
872 find . -type f -name "*1*" -or -name "*2*" -print
873 find . -type f -name "*1*" -and -name "*2*" -print
875 The `find` command can acquire a list of files and perform some
876 operation on each file. Try this command out:
878 find . -type f -exec grep Volume {} \;
880 This command finds every file starting from `.`. Then it searches each
881 file for a line which contains the word "Volume". The `{}` refers to
882 the name of each file. The trailing `\;` is used to terminate the
883 command. This command is slow, because it is calling a new instance
884 of `grep` for each item the `find` returns.
886 A faster way to do this is to use the `xargs` command:
888 find . -type f -print | xargs grep Volume
890 `find` generates a list of all the files we are interested in,
891 then we pipe them to `xargs`. `xargs` takes the items given to it
892 and passes them as arguments to `grep`. `xargs` generally only creates
893 a single instance of `grep` (or whatever program it is running).
898 Navigate to the `data` directory. Use one find command to perform each
899 of the operations listed below (except number 2, which does not
900 require a find command):
902 1. Find any file whose name is "NOTES" within `data` and delete it
904 2. Create a new directory called `cleaneddata`
906 3. Move all of the files within `data` to the `cleaneddata` directory
908 4. Rename all of the files to ensure that they end in `.txt` (note:
909 it is ok for the file name to end in `.txt.txt`
911 Hint: If you make a mistake and need to start over just do the
914 1. Navigate to the `shell` directory
916 2. Delete the `data` directory
918 3. Enter the command: `git checkout -- data` You should see that the
919 data directory has reappeared in its original state
923 Redo exercise 4, except rename only the files which do not already end
924 in `.txt`. You will have to use the `man` command to figure out how to
925 search for files which do not match a certain name.
933 **backtick, xargs**: Example find all files with certain text
937 **variables** -> use a path example
947 **Regular Expressions**
951 **Chaining commands together**