命令行基础知识

朱雀 2022-07-16 04:58 153阅读 0赞

（1）基础知识

一：

$ cd 2015

1.     cd stands for "change directory". Just as you would click on a folder in Windows Explorer or Finder, cd switches you into the directory you specify. In otherwords, cdchanges the workingdirectory.

2.     The directory we change intois 2015. When a file, directory orprogram is passed into a command, it is called an *argument*. Herethe 2015 directory is an argument for the cd command.

The cd commandtakes a directory name as an argument, and switches into thatdirectory.

二：

$ pwd /home/ccuser/workspace/blog

`pwd` stands for "print working directory". It out puts the name of the directory you are currently in, called the *working directory*.

Here the working directory is **blog/**. In Codecademy courses, your working directory is usually inside the **home/ccuser/workspace/** directory.

Together with `ls`, the `pwd` commandis useful to show where you are in the filesystem.

三：

$ cd ..

To move up one directory, use `cd ..`. Here, `cd ..` navigates up from **jan/memory/** to **jan/**.

四：

$ mkdir media

The `mkdir` command stands for"make directory". It takes in a directory name as an argument, and then creates a new directory in the current working directory.

Here we used `mkdir` to createa new directory named **media/**insidethe **feb/** directory.

** **

**五：**

touch keyboard.txt

The `touch` command creates a new file inside the working directory. It takes in a filename as an argument,and then creates an empty file in the current working directory.

Here we used `touch` to createa new file named **keyboard.txt **insidethe **2014/dec/** directory.

** **

**六：小结**

From the command line, you can navigate through files andfolders on your computer:

·        pwd outputs the name of thecurrent working directory.

·        ls lists all files anddirectories in the working directory.

·        cd switches you into thedirectory you specify.

·        mkdir creates a new directoryin the working directory.

·        touch creates a new fileinside the working directory.

（2）浏览和修改文件系统

**七：**

$ ls -a . .. .preferences action drama comedygenres.xt

1.     The ls command lists all files and directories in the working directory.

2.     The \-a modifies the behavior of the ls command to also list the files and directories starting with a dot (.). Files started with a dot are hidden, and don't appear when using ls alone.

The \-a is called an *option*. Options modify the behavior of commands. Here we used ls -a to displaythe contents of the working directory in more detail.

In additionto \-a, the ls command has several more options. Here are three common options:

·        \-a - lists all contents,including hidden files and directories

·        \-l - lists all contents ofa directory in long format

·        \-t - order files anddirectories by the time they were last modified.

**八：**

$ ls -l drwxr-xr-x 5 cc eng 4096 Jun 24 16:51action drwxr-xr-x 4 cc eng 4096 Jun 24 16:51 comedy drwxr-xr-x 6 cc eng 4096Jun 24 16:51 drama -rw-r--r-- 1 cc eng 0 Jun 24 16:51 genres.txt

The \-l option lists files anddirectories as a table. Here there are four rows, with seven columns separatedby spaces. Here's what each column means:

1.     Access rights. These areactions that are permitted on a file or directory.

2.     Number of hard links. Thisnumber counts the number of child directories and files. This number includesthe parent directory link (..) and current directory link(.).

3.     The username of the file's owner.Here the username iscc.

4.     The name of the group thatowns the file. Here the group name is eng.

5.     The size of the file inbytes.

6.     The date & time that thefile was last modified.

7.     The name of the file ordirectory.

**九：**

$ ls -alt

drwxr-xr-x 4 cc eng 4096 Jun 29 12:22 .

-rw-r--r-- 1 cc eng 0 Jun 29 12:22 .gitignore drwxr-xr-x 5 cc eng 4096 Jun 30 14:20 ..

drwxr-xr-x 2 cc eng 4096 Jun 29 12:22 satire drwxr-xr-x 2 cc eng 4096 Jun 29 12:22 slapstick -rw-r--r-- 1 cc eng 14 Jun 29 12:22 the-office.txt

The `-t` option orders filesand directories by the time they were last modified.

Inaddition to using each option separately, like `ls -a` or`ls -l`, multiple options can be used together,like `ls -alt`.

Here, `ls -alt` lists allcontents, including hidden files and directories, in long format, ordered bythe date and time they were last modified.

** **

**十：**

cp frida.txt lincoln.txt

The `cp` command copies files or directories. Here, we copy the contents of **frida.txt** into **lincoln.txt**.

** **

**十一：**

cp biopic/cleopatra.txt historical/

To copy a file into a directory, use `cp` with the source file as the first argument and the destination directory as the second argument. Here, we copy the file **biopic/cleopatra.txt** and place it in the **historical/** directory.

cp biopic/ray.txt biopic/notorious.txt historical/

To copy multiple files into a directory, use `cp` with a list of source files as the first arguments, and the destination directory as the last argument. Here, we copy the files **biopic/ray.txt **and **biopic/notorious.txt** into the **historical/** directory.

** **

十二：

cp * satire/

Inaddition to using filenames as arguments, we can use special characters like `*` to select groups offiles. These special characters are called *wildcards*. The `*` selectsall files in the working directory, so here we use `cp` to copy all files into the **satire/** directory.

cp m*.txt scifi/

Here, `m*.txt` selects all files in the working directory starting with "m" and ending with".txt", and copies them to ***scifi/***.

十三：

The `mv` command moves files.It's similar to `cp` in itsusage.

mv superman.txt superhero/

To move a file into a directory, use `mv` with the source file as the first argument and the destination directory as the second argument. Here we move **superman.txt** into **superhero/**.

mv wonderwoman.txt batman.txt superhero/

To move multiple files into a directory, use `mv` with a list of source files as the first arguments, and the destination directory asthe last argument. Here, we move **wonderwoman.txt** and**batman.txt** into **superhero/**.

mv batman.txt spiderman.txt

To rename a file, use `mv` with the old file as the first argument and the new file as the second argument. By moving **batman.txt** into **spiderman.txt**,we rename the file as **spiderman.txt**.

十四：

rm waterboy.txt

The `rm` command deletes filesand directories. Here we remove the file **waterboy.txt** from the filesystem.

rm -r comedy

The `-r` is an option that modifies the behavior of the `rm `command. The `-r` stands for"recursive," and it's used to delete a directory and all of its child directories.

Be careful when you use `rm`! It deletes files and directories permanently. There isn't an undelete command, so once you delete a file or directory with `rm`, it's gone.

十五：总结

·        Options modify the behavior of commands:

o    ls -a lists all contents of a directory, including hidden files and directories

o    ls -l lists all contents in long format

o    ls -t orders files and directories by the time they were last modified

o    Multiple options can be used together, like ls -alt

·        From the command line, you can also copy, move, and remove files and directories:

o    cp copies files

o    mv moves and renames files

o    rm removes files

o    rm -r removes directories

·        Wildcards are useful for selecting groups of filesand directories

（3）重定向输入输出

一：

$ echo "Hello"

Hello

The `echo` command accepts the string "Hello" as *standard input*, and echoes the string "Hello"back to the terminal as *standard output*.

Let's learn more about standard input, standard output, and standard error:

1.     *standard input*,abbreviated as `stdin`, is information inputted into the terminal through the keyboard or input device.

2.     *standard output*,abbreviated as `stdout`, is the information outputted after a process is run.

3.     *standard error*,abbreviated as `stderr`, is an error message outputted by a failed process.

Redirection reroutes standard input, standard output,and standard error to or from a different location.

二：

$ echo "Hello" > hello.txt

The `>` command redirects the standard output to a file. Here,`"Hello"` is entered as the standard input. The standard output`"Hello"` is redirected by `>` to the file **hello.txt**.

$ cat hello.txt

The `cat` command outputs the contents of a file to the terminal. When you type `cathello.txt`, the contents of **hello.txt** are displayed.

三：

$ cat oceans.txt > continents.txt

`>` takes the standard output of the command on the left, and redirects it to the file on the right. Here the standard output of`catoceans.txt` is redirected to **continents.txt**.

Note that `>` overwrites all original content in **continents.txt**.When you view the output data by typing `cat` on **continents.txt**,you will see only the contents of **oceans.txt**.

四：

$ cat glaciers.txt >> rivers.txt

`>>` takes the standard output of the command on the left and *appends* (adds) it to the file on the right. You can view the output data of the file with `cat` and the filename.

Here, the output data of **rivers.txt** will contain the original contents of **rivers.txt** with the content of **glaciers.txt**appended to it.

五：

$ cat < lakes.txt

`<` takes the standard input from the file on the right and inputs it into the program on the left. Here, **lakes.txt** is the standard input for the `cat` command. The standard output appears in the terminal.

六：

$ cat volcanoes.txt | wc

`|` is a"pipe". The `|` takes the standard output of the command on the left, and *pipes* it as standard input to the command on the right. You can think of this as "command to command" redirection.

Here the output of `cat volcanoes.txt` is the standard input of  `wc`. in turn, the `wc` command outputs the number of lines, words, and characters in `volcanoes.txt`, respectively.

$ cat volcanoes.txt | wc | cat > islands.txt

Multiple `|`s can bechained together. Here the standard output of `cat volcanoes.txt` is "piped"to the `wc` command.The standard output of `wc` is then"piped" to `cat`. Finally, the standard output of `cat` is redirected to `islands.txt`.

You can view the output data of this chain by typing`cat islands.txt`.

七：

$ sort lakes.txt

`sort` takes the standard input and orders it alphabetically for the standard output. Here, the lakes in `sort lakes.txt` are listed in alphabetical order.

$ cat lakes.txt | sort > sorted-lakes.txt

Here, the command takes the standard output from `cat lakes.txt` and"pipes" it to `sort`. The standard output of `sort` is redirected to **sorted-lakes.txt**.

You can view the output data by typing `cat` on the file **sorted-lakes.txt**.

八：

uniq deserts.txt

`uniq` standsfor "unique" and filters out adjacent, duplicate lines in a file.Here `uniq deserts.txt` filters out duplicates of "Sahara Desert", because the duplicate of 'SaharaDesert' directly follows the previous instance. The "Kalahari Desert"duplicates are not adjacent, and thus remain.

$ sort deserts.txt | uniq

A more effective way to call `uniq` is to call `sort` to alphabetize a file, and "pipe" the standard output to `uniq`. Here by piping `sort deserts.txt` to `uniq`, all duplicate lines are alphabetized (and thereby made adjacent) and filtered out.

sort deserts.txt | uniq > uniq-deserts.txt

九：

$ grep Mount mountains.txt

`grep` standsfor "global regular expression print".It searches files for lines that match a pattern and returns the results. It is also case sensitive. Here, `grep` searches for "Mount" in **mountains.txt**.

$ grep -i Mount mountains.txt

`grep -i` enables the command to be case insensitive. Here,`grep` searches for capitalor lowercase strings that match `Mount` in **mountains.txt**.

The above commands are a great way to get started with `grep`. If you are familiar with regular expressions, you can use regular expressions to search for patterns in files.

十：

$ grep -R Arctic /home/ccuser/workspace/geography

`grep -R` searches all files in a directory and outputs filenames and lines containing matched results. `-R` standsfor "recursive". Here `grep -R` searches the **/home/ccuser/workspace/geography** directory for the string"Arctic" and outputs filenames and lines with matched results.

$ grep -Rl Arctic /home/ccuser/workspace/geography

`grep -Rl` searches all files in a directory and outputs only filenames with matched results. `-R` stands for"recursive" and `l` stands for"files with matches". Here `grep -Rl` searches the**/home/ccuser/workspace/geography** directory for the string"Arctic" and outputs filenames with matched results.

十一：查找和替换

sed 's/snow/rain/' forests.txt

sed stands for "streameditor". It accepts standard input and modifies it based on an *expression*, before displaying it as output data. It is similar to "find and replace".

Let's look at the expression 's/snow/rain/':

·        s: stands for"substitution". it is *always* used when using sed for substitution.

·        snow: the search string, the text to find.

·        rain: the replacement string, the text to add in place.

In this case, sed searches **forests.txt** for the word "snow"and replaces it with "rain." Importantly, the above command will only replace the first instance of "snow" on a line.

$ sed 's/snow/rain/g' forests.txt

The above command uses the g expression, meaning "global". Here sed searches **forests.txt** for the word "snow" and replaces it with "rain", *globally*. All instances of "snow" on a line will be turned to"rain".

十二：小结

·        *Redirection* reroutes standardinput, standard output, and standard error.

·        The common redirection commands are:

o    > redirects standard output of a command to a file, overwriting previous content.

o    >> redirects standard output of a command to afile, appending new content to old content.

o    < redirects standard input to a command.

o    | redirects standard output of a command to another command.

·        A number of other commands are powerful when combined with redirection commands:

o    sort: sorts lines of text alphabetically.

o    uniq: filters duplicate, adjacent lines of text.

o    grep: searches for a text pattern and outputs it.

o    sed : searches for a text pattern, modifies it, andoutputs it.

（4）配置环境

一：

$ nano hello.txt

*nano* is a command line text editor. It works just like a desktop text editor like TextEdit or Notepad, except that it is accessible from the command line and only accepts keyboard input.

1.     The command nano hello.txt opens a new text file named **hello.txt** in the nano texteditor.

2.     "Hello, I am nano" is a text string entered in nano through the cursor.

3.     The menu of keyboard command sat the bottom of the window allow us to save changes to **hello.txt** and exit nano. The ^ stands for the Ctrl key.

4.     Ctrl + O saves a file. 'O' stands for output.

5.     Ctrl + X exits the nano program. 'X' stands for exit.

6.     Ctrl + G opens a help menu.

7.     clear clears the terminal window, moving the commandprompt to the top of the screen.

二：

You created a file in nano called **~/.bash\_profile** and added a greeting. How does this work?

$ nano ~/.bash\_profile

**~/.bash\_profile** is the name of file used to store environment settings. It is commonly called the "bash profile". When a session starts, it will load the contents of the bash profile before executing commands.

·        The ~ represents the user's home directory.

·        The . indicates a hiddenfile.

·        The name **~/.bash\_profile** is important, since this is how the command line recognizes the bash profile.

1.     The command nano ~/.bash\_profile opens up**~/.bash\_profile** in nano.

2.     The text echo "Welcome, Jane Doe" creates a greeting in the bash profile, which is saved. It tells the command line to echo the string "Welcome, Jane Doe" when a terminal session begins.

3.     The command source ~/.bash\_profile activates the changes in **~/.bash\_profile** for the current session. Instead of closing the terminal and needing to start a new session, source makes the changes available right away in the session we are in.

三：创建快捷方式

alias pd="pwd"

The alias command allows you to create keyboard shortcuts, or aliases, for commonly used commands.

1.     Here alias pd="pwd" creates the alias pd for the pwdcommand, which is then savedin the bash profile. Each time you enter pd, the output will be the same as thepwd command.

2.     The command source ~/.bash\_profile makes the aliaspd available in the current session.

四：

export USER="Jane Doe"

*environment variables* are variables that can be used across commands and programs and hold information about the environment.

1.     The line USER="Jane Doe" sets the environment variable USER to a name "Jane Doe". Usually the USER variable is set to the name of the computer's owner.

2.     The line export makes the variable to be available to all child sessions initiated from the session you are in. This is a way to make the variable persist across programs.

3.     At the command line, the command echo $USER returns the value of the variable. Note that $ is always used when returning a variable's value. Here, the command echo $USER returns the name set for the variable.

五:

export PS1=">> "

PS1 is a variable that defines the makeup and style of the command prompt.

1.     export PS1=">> " sets the command prompt variable and exports the variable. Here we change the default command promptfrom $to >>.

2.     After using the source command, the command line displays the new command prompt.

六:

$ echo $HOME

The HOME variableis an environment variable that displays the path of the home directory. Here by typing echo $HOME, the terminal displays the path**/home/ccuser** as output.

七:

$ echo $PATH/home/ccuser/.gem/ruby/2.0.0/bin:/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/sbin:/sbin:/bin

PATH is an environment variable that stores a list of directories separated by a colon. Looking carefully,echo $PATH lists the following directories:

1.     /home/ccuser/.gem/ruby/2.0.0/bin

2.     /usr/local/sbin

3.     /usr/local/bin

4.     /usr/bin

5.     /usr/sbin

6.     /sbin

7.     /bin

Each directory contains scripts for the command line to execute. The PATH variables imply lists which directories contain scripts.

八:小结