Bash Commands⚓︎
Use this sheet to test yourself! Click the box for unfolding.
ls⚓︎
ls -l
Check the components in the current directory; with detailed information. The authority meaning of the first column:
cd⚓︎
pwd⚓︎
grep⚓︎
grep -i
Search a string
in the file
directory, with case-insensitive. The output will mix both up & low -case
results.
The case below will search: What
, WhaT
, wHAt
, wHat
, .etc.
grep -r
Search a string
from all files in the current directory
(or in a given file
if send the parameter) and in all of its subdirectories
.
chmod⚓︎
chmod
Set authority
for the given file.
Note that: there are two ways to use chmod. For example, chmod 644 <filename>
and chmod u+rw <filename>
Person | user | group | other |
---|---|---|---|
Decimal | 6 | 4 | 4 |
Binary | 110 | 100 | 100 |
Meaning | rwx | rwx | rwx |
Person | u | g | o |
---|---|---|---|
Meaning | user | group | other |
Verb | + | - |
---|---|---|
Meaning | add | remove |
Behavior | r | w | x |
---|---|---|---|
Meaning | read | write | excute |
find⚓︎
history⚓︎
Pip (|)⚓︎
|
-- pip operator
Combine two or more commands.
e.g. I want to use history
and grep ls
in sequence. I use history | grep ls
Output Redirect (>)⚓︎
>
-- output redirection operator
Redirect the contents of a command/file to another by overwriting
it.
e.g.
I want to save the output of history | grep ls
in the file output.log
. I use history | grep ls > output.log
.
cat⚓︎
cat
Print
the content of a file
onto the standard output stream.
cat
is primarily used for displaying the entire contents of one or more text files in the terminal.
less
is a pager utility designed for viewing and navigating through large text files or long outputs that don't fit on a single screen.
man⚓︎
man
The function of man
is like --help
(in GitBash). It shows the manual pages
for a command.
e.g. I want to check less
command using manu:
more, less, most⚓︎
more, less, most
The three commands are used to view the text files in the command prompt, displaying one screen at a time in case the file is large (For example log files).
- Support
forward navigation
andlimited backward navigation
.
- Support both
forward navigation
andbackward navigation
. - Has
search
options. - Can go to the
beginning
and theend
of a file instantly. - Can switch to an
editor
(like opening the file invi
orvim
).
Arrow keys
: Scroll up and down.
/
: Start a forward search.
?
: Start a backward search.
n
: Move to the next search result.
N
: Move to the previous search result.
q
: Quit the less viewer.
It is noticeably quicker than editor when the file is large.
- Has
all
the features ofmore
andless
. - Can also open
multiple files
, close 1 file at a time when you have multiple files open. - Allows
locking
andscrolling
of the open windows. - Allows for
splitting
of open windows.
alias⚓︎
alias
Create a shortcut
that references a command.
e.g. Create a shortcut for ls -la
as ll
: alias ll="ls -la"
unalias⚓︎
unalias
Remove alias
.
Note
unalias
not only remove the alias
from the current session but also remove them permanently from shell's configuration file
.
echo⚓︎
echo
A built-in Linux feature that prints out arguments as the standard output
. Example see in PATH.
which⚓︎
PATH⚓︎
PATH
edit
Q: How to make scripts execute from the present working directory without having to type a ./
before the script's name (e.g. hello
instead of ./hello
)?
A: ./
executes files that are not in ${PATH}
, “.” means it directly execute file in the current directory. Thus, we need to add hello’s absolute directory in ${PATH}
, such as:
PATH DEFAULT=${PATH}:/path/to/hello
ln⚓︎
ln -s
Create a soft link
for an existing file.
Grammar: ln -s <a: original file> <b: soft link file>
We can use rm -rf <b>
to delete the soft link.
Background Processing (&)⚓︎
&
For example, launching Node.js using node app.js &
vs. node app.js
Use the background process
can help to keep the process running without terminal effects. However, a foreground process
will be killed when we close the terminal.
code⚓︎
code
Open VS Code
to edit some file.
source⚓︎
source
source
is used to read and execute the content of a file (generally a set of commands) right now instead of relaunching the shell. Those commands are passed as an argument in the current shell script.
Let's create a .bash_profile
in the root
directory:
Then execute the file:
Oh no! All the dependencies have gone!
😆 Do not worry about it. Remove the code in .bash_profile
and relaunch your shell. Then your shell will be brand new! (The theory see in next topic .bash_profile vs .bashrc).
There is another way to fix the problem: change export PATH=.:
into export PATH=.:$PATH
.
.bash_profile vs .bashrc⚓︎
.bash_profile
v.s. .bashrc
When invoked, Bash
reads and excutes commands from a set of startup files, which is read depending on whether shell (command explainer)
is invoked as [interactive/non-interactive] or [login/non-login] shell.
Shell type | interactive | non-interactive | login | non-login |
---|---|---|---|---|
Example | terminal (shell read, write) | non-terminal (execute a script) | remotely (via ssh) | locally |
For: Interactive log-in shell.
For: Interactive non-login shell.
Note!
The components you write in .bash_profile
and .bashrc
is just appending more works to the current default shell settings. It is not overlapping.
E.g. situations
- If you create an empty
.bash_profile
and execute (usesource
) immediately, it will make any changes to your shell's setting. - If you make any changes in
.bash_profile
and execute it immediately, it will implement the changes in your shell. However, if you delete the code in.bash_profile
for the changes and restart shell, the shell will run as the original default.
Shebang (#!)⚓︎
#!
Bash
commands can be used not only in command lines but also in scripts. The head of Bash script
should mention using Bash shell with #!
.
e.g: With #!/bin/bash
, generate SHA hash for [A-Za-z0-9]
: (More bashscript learning)
How to run a bash script?
There are two ways to run a bash script:
-
Use
source
. Source it immediately! -
Make it executable with
chmod 7xx <script_name>
. Then run it in any way below. Let's assume the script is namedDonow
:- Add script path into
PATH
. Then Run it with script name. e.g.:$ Donow
- Run relative path. e.g.:
$ ./Donow
- Run absolute path. e.g.:
$ <Path_from_root>/Donow
- Add script path into
sha1sum⚓︎
sha1sum
sha1sum
is a cryptographic hash function. The algorithm transfer data into Checksum
, which is convenient for confirming if your copy is the same as the original one.
folder⚓︎
cp
-
To copy a file to another location:
cp <sourcefile> <destination>
e.g. cp myfile.txt /path/to/destination/
-
To copy a folder and its contents recursively:
cp -r <sourcefolder> <destination>
e.g. cp -r myfolder/ /path/to/destination/
mv
-
To move(cut) a file to another location:
cp <sourcefile> <destination>
e.g. mv myfile.txt /path/to/destination/
-
To move(cut) a folder and its contents recursively:
cp <sourcefolder> <destination>
e.g. mv myfolder/ /path/to/destination/
rmdir
Clear folder; rmdir
only works on empty directories. If a directory contains files or subdirectories, rmdir
will not remove it and will display an error message.
rm -rf
rm -rf
is used for forcefully and recursively removing directories and their contents, including non-empty directories.
-f
force; delete without informing and ignore unexistant files/para.r
recursive; recursivly delete the directory and its contents.
du -h
Used to display the size of a directory or file.
-h
human-readable; In units K, M, G, improve the readability of information.
disk⚓︎
df -T -h
Disk free (df
); Check disk space usage:
-T:
This option is used to display the file system type for each file system.
-h
: This option is used to display sizes in a human-readable format (e.g., in gigabytes, megabytes, etc.) rather than in raw blocks.
fdisk -l
Fixed disk (fdisk
); List disk partitions:
-l
: This option stands for "list" and is used to list the partition table for all available storage devices.
mount
Mount Disk Partitions:
Grammar: mount -t <filesystem_type> <device> <mount_point>
<device>
: This should be replaced with the device or partition you want to mount. It can be specified as a device file, such as /dev/sda1, or a UUID (Universally Unique Identifier) for the device.
<mount_point>
: This should be replaced with the directory where you want to mount the file system. This directory should already exist. For example, if you want to mount the file system on a directory called /mnt/mydata, you would replace
-
Mount an ISO9660 file system (e.g., for CD/DVD):
mount -t iso9660 <device> <mount_point>
-
Mount a VFAT (FAT32) file system:
mount -t vfat <device> <mount_point>
-
Mount a ext4 file system:
mount -t ext4 <device> <mount_point>
umount
Unmount a specific device (replace
umount <mount_point>
Unmount all mounted filesystems:
umount -a
ZIP⚓︎
Compress
-
Compress a file or directory into a
.tar.gz
file:tar -czvf archive.tar.gz file1 file2 ...
-
Compress a file or directory into a
.tar.bz2
file:tar -cjvf archive.tar.bz2 file1 file2 ...
-
Compress a file or directory into a
.zip
file:zip -r archive.zip file1 file2 ...
-c
: This option stands for "create" and instructs tar to create a new archive.
-v
: This option stands for "verbose" and makes tar display the names of the files it is archiving as it processes them. It provides additional information during the archiving process.
-f
: filename.tar: This option specifies the filename of the tar archive that will be created. In this case, it will be named filename.tar.
-z/-j:
For gzip/bzip2 compressed or decompressed algorithms.
-r
: This option stands for "append." It instructs tar to add files or directories to an existing tar archive.
DeCompress
-
Extract files from a
.tar.gz
archive:tar -xzvf archive.tar.gz
-
Extract files from a
.tar.bz2
archive:tar -xjvf archive.tar.bz2
-
Extract files from a
.zip
archive:unzip archive.zip
Networking⚓︎
ifconfig
Display Network Interface Parameters: this command is used to display information about network interfaces on your system, including IP addresses, MAC addresses, and other network-related settings.
ping
Check Connectivity: the ping
command is used to test network connectivity to a specific IP address (replace xxx.xxx.xxx.xxx with the target IP address). It sends ICMP echo request packets to the target and waits for responses, allowing you to check if a remote host is reachable.
netstat
Display Network Status: the netstat
command is used to display network-related information. It provides various options to control what information is displayed:
-a
: Shows all sockets (both listening and non-listening).
-l
: Includes listening sockets.
-n
: Displays numerical IP addresses instead of resolving hostnames.
-o
: Shows additional information.
-r
: Displays the routing table.
-t
: Lists only TCP sockets.
-u
: Lists only UDP sockets.
-w
: Lists only raw sockets.
-x
: Lists only Unix Domain sockets.
Process⚓︎
ps
The ps
command is used to display information about running processes on the system.
pgrep
The pgrep
command is used to search for processes based on their names or other attributes and retrieve their PIDs (Process IDs).
top
The top
command provides a dynamic, real-time view of system processes and their resource usage.
kill
use kill
when you know the specific PID of the process you want to terminate.
kill 1234
use pkill
when you want to terminate processes based on their names or attributes.
pkill myprocess
Created: December 4, 2022 23:35:51