command lline 学习笔记

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

-l - lists all contents of a directory in long format

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

1.==Access rights==. These are actions that are permitted on a file or directory.
2.==Number of hard links==. This number counts the number of child directories and files. This number includes the parent directory link (..) and current directory link (.).
3.==The username of the file’s owner==. Here the username is cc.
4.==The name of the group that owns the file==. Here the group name is eng.
5.The ==size== of the file in bytes.
6.The ==date & time== that the file was ==last modified==.
7.The ==name== of the file or directory.

-t - order files and directories by the time they were last modified.
-alt - multiple options are used together

1. -[filename1] [filename2] - copy the contents of filename1 into filename2.
2. -[filename1] [filename2] [path] - a new copy of filename1 and filename1 in [path] directory.
3. -* - copy all files
4. -m*.txt - copy all files starting with “m” and ending with “txt”

1. -[filename1] [filename2] - rename a file

1. The rm command deletes files and directories.
2. 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.
3. Be careful when you use rm! It deletes files and directories permanently.

1. echo "Hello" > hello.txt - The > command redirects the standard output to a file.
2. cat hello.txt - The cat command outputs the contents of a file to the terminal.
3. cat oceans.txt > continents.txt - > takes the standard output of the command on the left, and redirects it to the file on the right. Note that - - > overwrites all original content in continents.txt.
4. 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.
5. cat < lakes.txt - < takes the standard input from the file on the right and inputs it into the program on the left.
6. 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.
7. wc - wc command outputs the number of lines, words, and characters in volcanoes.txt, respectively.
8. sort lakes.txt - sort takes the standard input and orders it alphabetically for the standard output.
9. uniq - filter out adjacent, duplicate lines in a file.

• grep Mount mountains.txt - grep stands for “global regular expression print”. It searches files for lines that match a pattern and returns the results.

1. grep -i - be case insensitive.
2. grep -R - searches all files in a directory and outputs filenames and lines containing matched results. -R stands for “recursive”
3. 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”.

• sed 's/snow/rain/[g]' forests.txt - sed stands for “”. It accepts standard input and modifies it based on an expression, before displaying it as output data. It is similar to “find and replace”.

1. s - stands for “substitution”. it is always used when using sed for substitution.
2. snow - the search string, the text to find.
3. rain - the replacement string, the text to add in place.
   the above command will only replace the first instance of “snow” on a line.
4. g - means “global”

~/.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 hidden file.
• 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.