Bash Command 101

vim

link: https://www.keycdn.com/blog/vim-commands

There are two modes in vim command: command mode and insert mode. We will go through some frequent usages.

Basic commands

1. :help [keyword]: this command will help you find out the helpful documentation of the [keyword] you type.
2. :e [filename]: this command will open a file. You need to provide the directory path of the file in the [filename].
3. :w: this command will save the current file.
4. :wq: this command will save the current file and quit vim.
5. :q!: this command will quit the vim without saving the file.

Movement

1. h: move the cursor one charactor to the left.
2. l: move the cursor one charactor to the right.
3. j: move the cursor down one line.
4. k: move the cursor up one line.
5. b: move the cursor one word to the left.
6. w: move the cursor one word to the right.
7. 0: move the cursor to the beginning of the line.
8. $: move the cursor to the end of the line.
9. gg: move the cursor to the beginning of the file.
10. G: move the cursor the end of the file.
11. :#: # is the number of a line. Move the cursor to that line.

You can add a count in front of one command to make Vim complete a command multiple times.

Editing

1. v: highlight one charactor per time
2. V: highlight one line per time
3. y: yank highlighted contents
4. p: paste whatever has been copied after the current line
5. P: paste whatever has been copied on the current line
6. d: delete highlighted contents
7. dd: delete current line
8. u: undo the last operation
9. Ctrl+r: Redo the last undo
10. .: repeat the last action

Searching

1. /[keyword]: searches for text in the document from the beginning to the end of the file.
2. ?[keyword]: searches for text in the document from the end to the beginnign of the file.
3. n: Find next appearance
4. N: Find previous appearance
5. :%s/[pattern]/[replacement]/gc: replaces all occurrences of a pattern and confirms each one.

---

grep

You can use grep to search some pattern in a file.

Basic syntax

grep pattern filename

Useful arguments

1. -n: show matching line numbers
2. -c: count the number of occurrence
3. -r: perform recursive search

grep -r "string" /home/: search “string” in all files in the home directory and all its subdirctories.

Together with other commands

1. find out process pid

ps -ef | grep someprocess

---

ls

ls is used to list files or directories in Linux system. You can do more than what you expect by leveraging powerful arguments.

Useful arguments

1. ls -l: list the contents of the directory in a table with columns including
   1. content permissions
   2. number of links to the content
   3. owner of the content
   4. group owner of the content
   5. size of the content in bytes
   6. last modified date/time of the content
   7. file or directory name
2. ls -s: list files or directories with their sizes.
3. ls -S: list files or directories and sort by size in descending order. You can also add a -r to reverse the order.
4. ls -lh: list files or directories in the same table format as -l, but with readable file sizes
5. ls -a: list files or directories including hidden files or directories.
6. ls -t: list files or directories and sort by last modified date in descending order. You can also add a -r flag to reverse the order.

---

touch

You can use touch to create a new file, like touch filename

---

sed

You can use sed to manipulte and edit text files without even opening them.

Basic syntax

sed [operation] filename

Useful usages

1. substitute or replace a string

   sed 's/pattern/replacement' filename > s in the command is the replacement indicator and / in the command is the delimiter By default, sed will only replace the first occurrence in a line.

2. substitute or replace a string(all occurrences)

   sed 's/pattern/replacement/g' filename

3. substitute or replace a string in a specific range of lines

   sed 'line1,line2 s/pattern/replacement/g' filename The range is from line1 to line2.

---

cat

cat is short for concatenate. You can use this command to show contents of a file or concatenate files together.

Basic syntax

cat filename
cat > filename

Useful usages

1. display contents of a file

   cat filename

2. concatenate files together to a new file

   cat filename1 filename2 > newfile

3. copy one file

   cat filename1 > filename2 > > is printout redirection. It will redirect std out to file. < is printin redirection.

4. append one file to another

   cat filename1 >> filename2

---

ps

ps will report a snapshot of the current processes.

Basic syntax

ps [options]

Useful arguments

1. ps -ef: print out all processes. Use System V style.
2. ps aux: same as ps -ef. Use BSD sytle.

---

top

---

kill

---

df

df is short for disk free, which is used to show the amount of free disk space available on Linux system and to understand the filesystems that have been mounted.

Useful arguments

1. df -h: show all filesystems and their disk usage in human-readable form.
2. df /path/to/directory_or_file: show the filesystem and its disk usage containing the given file or directory

---

du

---

chmod

chmod sets the permissions of files or directories. Permissions defines the permissions for owner of the file(user), members of the group who owns the file(group), and anyone else(others).

For example, if we want to set the permission like below:

1. User can read, write and execute
2. Group can read, write and execute
3. Others can read and execute

You can use command：chmod u=rwx,g=rwx,o=rx filename </br> Or you can use equivalent command: chmod 775 filename where 4 stands for read, 2 stands for write, 1 stands for execute.

---

ping

ping can test the connectivity to a specific destination computer by sending one or more ICMP Echo Request packages.

Basic syntax

ping [options] URL

---

wget

wget lets you download files form the web. It supports background running.

Basic syntax

wget [options] URL

---

curl

curl can transfer data from or to a server without user interaction.

Basic syntax

curl [options] URL

Useful usages

1. retrieve the homepage

   curl example.com

2. save the output to a file

   curl -O url_address > curl -o filename url_address > -O will resue its original filename.

3. get the headers of a url

   curl -I url_address

---

xargs

xargs allows you to build and execute commands from standard input.

Useful usages

echo "filename" | xargs touch is equivalent to touch filename

---

ssh

---

find

---

mount