Unix/Linux Terminal

Table of Contents

Opening the Terminal
Keyboard Shortcuts
File System
Basics of Linux/Unix Commands
Basic Commands
Package Manager
Run files on cmd
Listing directory contents & directory structure
Changing Permissions
Creating Directories
Creating Files
Redirecting Output
Editing a File
Reading File Content
Copying and Moving Files
Renaming Files
Deleting Files and Directories
Chaining Commands
Finding Strings and Counting Occurences
AWK

Opening the Terminal

Linux

Search for “terminal” in the apps menu in most cases. You might have to look up specific instructions for your distro. Default Keyboard shortcut: Ctrl + Alt + T

MacOS

Search for “terminal” in Spotlight. Keyboard shortcut: Control + Option + Shift + T

Windows

The in-built terminals on Windows (cmd and PowerShell) are not POSIX compliant, so you will need to do one of the following:

Install a POSIX-compatible runtime like MinGW or Cygwin.
Note that git-for-windows includes a MinGW installation called git-bash by default, and is usually located in C:\Program Files\Git\git-bash.exe
Enable the Windows Subsystem for Linux (WSL). WSL is a system developed by Microsoft that allows a full Linux OS to run alongside Windows.
Learn More about WSL | Install WSL
Use Docker containers. Docker allows programs to run in isolated environments called containers. Each container is like a fresh install of the respective OS. There are pre-built containers for many popular Linux distros like Ubuntu, Debian, CentOS, etc.
Get started with Docker

Keyboard shortcuts

Shortcut	Function
`Tab`	Complete file & directory names and to further iterate over files
`Shift` + `Tab`	Go back to the previous names
`↑` or `Ctrl` + `P`	Go to all the commands previously executed in that instance of the cmd, one by one
`↓` or `Ctrl` + `N`	Go towards the recent commands
`Ctrl` + `R`	Search your command history
`Ctrl` + `←`/`→`	Jump words
`Home` or `Ctrl`	Jump to the beginning and end of the line
`End` or `Ctrl` + `E`	Jump to the end of the line
`Ctrl` + `C`	Stop running processes in your terminal and bring back the prompt

File System

Let’s get a brief on the Linux file system. If you’ve used Windows, you would be familiar with C:, D: etc.
In Linux, directory structure starts with / symbol, which is referred as the root directory The ~(tilde) is shorthand for your home directory. Within your home directory, you will find common directories, such as Documents, Music, Video, etc.,

A Gist on the file system folders and their general functions.

Absolute and Relative Paths

An absolute or full path points to the same location in a file system regardless of the current working directory. To do that, it must start from the root directory.

An absolute path always starts with a forward slash (/), which represents the start of the filesystem.

Eg: /home/username is an absolute path.

By contrast, a relative path starts from some given working directory, avoiding the need to provide the full absolute path. A filename can be considered as a relative path based at the current working directory. If the working directory is not the file’s parent directory, a file not found error will result if the file is addressed by its name.

A relative path never starts with a forward slash (/).

A relative path can start with a

.
- Represents the CWD (Current Working Directory).
..
- Represents the parent directory of the CWD.
~
- Represents the home directory of the logged in user.

Eg: ../docs is a relative path

Basics of Linux/Unix Commands

Command Structure

The components of the command line are:

the command
any options required by the command
the command’s arguments (if required)

The general form of a UNIX command is: command [-option(s)] [argument(s)]

#only the command
clear

#command with option
ls -l

#command with argument
man pwd

#command with option and argument
rm -r project

Command Help

man <command> is used to display the user manual of any command that we can run on the terminal. It provides a detailed view of the command. eg: man ls.
help command provides documentation for builtin commands.

$ help pwd
pwd: pwd [-LP]
  Print the name of the current working directory.

  Options:
    -L  print the value of $PWD if it names the current working directory
    -P  print the physical directory, without any symbolic links

  By default, `pwd' behaves as if `-L' were specified.

  Exit Status:
  Returns 0 unless an invalid option is given or the current directory
  cannot be read.

Variables

Syntax: ${var_name} or $var_name

Pre-defined variables: $HOME, etc…

Custom variables:

$ foo=bar
$ echo ${foo}
bar

NOTE: Strings in bash can be defined with ' and " delimiters, but they are not equivalent. Strings delimited with ' are literal strings and will not substitute variable values whereas " delimited strings will.

$ name=selena

$ echo 'Hey ${name}!'
Hey ${name}!

$ echo "Hey ${name}!"
Hey Selena!

Basic Commands

Print name of cwd (current working directory)

Use pwd to print name of current/working directory

$ pwd
/home/username

Clear screen & command history

Use clear or Ctrl + L to clear the screen of the cmd.
Use history to view the last 500 commands executed on the terminal.

Changing directories

$ pwd
/home/username

$ # providing an absolute path as argument
$ cd /etc
$ pwd
/etc

$ # to go back to previous working directory
$ # if there's a directory named '-', use './-' to go that directory
$ cd -
/home/username
$ pwd
/home/username

Relative paths are well, relative to current working directory
. refers to current directory
.. refers to directory one hierarchy above

../.. refers to directory two hierarchies above and so on

$ pwd
/home/username

$ # go to directory one hierarchy above
$ cd ..
$ pwd
/home

$ # go to directory 'username' present in current directory
$ # './' is optional in this case
$ cd ./username
$ pwd
/home/username

$ # go to directory two hierarchies above
$ cd ../..
$ pwd
/

NOTE:

About the Use of Dot-Slash (./) in Commands

Absolute vs Relative Path in Linux: What’s the Difference?

cd ~/ or cd ~ or cd will go to directory specified by HOME shell variable (which is usually set to user’s home directory)
```
$ pwd
/
$ echo "$HOME"
/home/username

$ cd
$ pwd
/home/username
```
Note: Specifying / at end of path argument is optional

Package manager

A package delivers and maintains new software for Linux-based computers. Just as Windows-based computers rely on executable installers, the Linux ecosystem depends on packages that are administered through software repositories.
Different Linux distros use different package managers. Ubuntu uses APT (Advanced Package Tool) to manage its packages.

Check for package updates

$ # To check if any packages on the system have updates
$ sudo apt-get update

$ # To update all packages
$ sudo apt-get upgrade

NOTE: Always run the update command before the upgrade command.

Install a package

$ sudo apt-get install <package_name>
$ # This might prompt you with a Y (yes) or n (no) option.

Remove a package

$ sudo apt-get remove <package_name>
$ # This might prompt you with a Y (yes) or n (no) option.

Run files on cmd

You can only run files if you have the permission to execute them. Refer Changing permissions section for more details.

$ ./file_to_run

Listing directory contents & directory structure

ls to list all files and directories in the cwd (current working directory).
```
$ ls
projects  report.log
```
ls path to view files in another directory without changing the cwd. The path can be absolute/relative.
```
$ ls /var/
backups  lib  lock  mail
```

Use the -a option to list all the files, including the hidden files and folders, in the cwd (current working directory).

$ ls
CODE_OF_CONDUCT.md  CONTRIBUTING.md  LICENSE  README.md  build  build.sh  src  temp.md

$ ls -a
.  ..  .git  .github  .gitignore  CODE_OF_CONDUCT.md  CONTRIBUTING.md  LICENSE  README.md  build  build.sh  src  temp.md

Use the -A option to print the same things as the -a option, but without printing . and ...

$ ls -a
.  ..  .git  .github  .gitignore  CODE_OF_CONDUCT.md  CONTRIBUTING.md  LICENSE  README.md  build  build.sh  src  temp.md

$ ls -A
.git  .github  .gitignore  CODE_OF_CONDUCT.md  CONTRIBUTING.md  LICENSE  README.md  build  build.sh  src  temp.md

Use the -l option for the long listing format. This format shows details like file permissions, ownership, size, timestamp, etc. (See changing permissions section for details on permissions, groups, etc)

$ ls -l
total 52
-rwxrwxrwx 1 harshkapadia harshkapadia  3431 Apr 21 23:09 CODE_OF_CONDUCT.md
-rwxrwxrwx 1 harshkapadia harshkapadia 20566 Apr 21 23:09 LICENSE
-rwxrwxrwx 1 harshkapadia harshkapadia  1253 Apr 21 23:09 README.md
drwxrwxrwx 1 harshkapadia harshkapadia  4096 Apr 22 00:48 build
...

tree to view directory structure.

It is not part of a standard Linux distribution, so you will need to install it.

$ # Install tree
$ sudo apt install tree

$ sudo tree
.
├── projects
│  ├── a.txt
│  ├── b.txt
│  └── backup
│    ├── a.txt
│    └── b.txt
└── report.log
2 directories, 5 files

Use which to find the location of a file.

$ which bash
/usr/bin/bash

Changing Permissions

In the output of ls -l command, the first 10 characters displayed are related to type of file and its permissions.

$ ls -l
total 84
lrwxrwxrwx 1 username eg  12 Mar 21 12:08 projects -> ../projects/
-rw-rw-r-- 1 username eg 39120 Feb 14  2019 report.log

First character indicates the file type The most common are

- regular file
d directory
l symbolic link
for complete list, see -l option in info ls

The other 9 characters represent three sets of file permissions for ‘user’, ‘group’ and ‘others’ - in that order

user file properties for owner of file G - u
group file properties for the group the file belongs to - g
others file properties for everyone else - o

Permission characters and values

Character	Meaning	Value	File	Directory
r	read	4	file can be read	can see contents of directory
w	write	2	file can be modified	can add/remove files in directory
x	execute	1	file can be run as a program	can access contents of directory
-	no permission	0	permission is disabled	permission is disabled

$ chmod 664 sample.txt

This means it will change the permission of sample.txt to rw-rw-r– i.e, user and group only have read and write permissions and others only have read permission.

Creating directories

mkdir dir_name will create a folder in the cwd, if the dir_name doesn’t already exist in the cwd.
Use "" if the dir_name has spaces, eg: mkdir "dir name".
Multiple folders can be created using mkdir {dir1,dir2,dir3}.
- Do not add any spaces in the curly brackets for the directory names.
Use the flag -p to create intermediate directories if they do not exist and not cause an error if they already exist.

# mkdir [option] dir_name
$ mkdir new_dir

# Spaces in directory name
$ mkdir "New Folder"

# Creating multiple directories
$ mkdir {dir1,dir2,dir3}

# Creating intermediate directories without causing errors if they already exist
$ mkdir -p public/css/summary public/html

Creating files

`touch` command

This is the easiest way to create a file in Linux.
```
$ touch sample.txt
```

Redirect operator (>)

This operator tells the system to output results into whatever you specify next. The target is usually a filename. You can use this symbol by itself to create a new file.
```
$ > sample.txt
```

`cat` command

The cat command is short for concatenate. It can be used to output the contents of several files, one file, or even part of a file. If the file doesn’t exist, the cat command will create it.
```
$ cat > sample.txt
```

`echo` command

The echo command will print out anything written after it.
```
$ echo Print this text
Print this text
```
It will print out environment variables like $HOME, $USER, $SHELL, $HOSTNAME, etc as well.
```
$ echo $SHELL
/bin/bash
```
It can be used to add text to a file using the output redirection operator. (It overwrites the contents of the entire file.)
```
$ cat sample.txt
Original text

$ echo New text! > sample.txt

$ cat sample.txt
New text!
```

It can be used to append text to a file using the output redirection operator.

$ cat sample.txt
Original text

$ echo New text! >> sample.txt

$ cat sample.txt
Original text
New text!

Using text editors

Vi Text Editor
```
$ vi sample.txt
```
Vim Text Editor
```
$ vim sample.txt
```
Nano Text Editor
```
$ nano sample.txt
```
Jump to Editing Files for more details.

Redirecting output

Redirect to a file

To redirect the output of a command to a file, use the > symbol.

Eg: ls -al > listings.txt will save the output of command ls -al is re-directed to listings.txt instead of your screen.

Note that if listings.txt already had some data, then this will overwrite the old data.

To append to an existing file, use the >> symbol.

Eg: ls -al >> listings.txt will append the output of command ls -al is re-directed to listings.txt.

Redirect to another command

Sometimes, it can be useful to use the output of one command as the input to another command. This can be achieved using pipes.
A pipe is created using the pip character (|).
Eg: To display output of a directory listing one page at a time, use ls -la | less.

Editing a file

Vi Text Editor

Vi is the oldest text editor in Linux. It was created alongside the Linux operating system for directly editing text files.
```
$ vi sample.txt
```
This will start the text editor in your terminal.
- Press the letter i to switch to insert mode, then type a few words to try it out.
- To save and exit press Esc :x and hit Enter.

Vim Text Editor

Vi editor wasn’t very user-friendly. Vim is a newer version, which stands for Vi editor, Modified.
```
$ vim sample.txt
```
This screen will look similar to the Vi editor screen.
- Press i to insert text, and type a few words.
- Save the file and exit by entering: Esc + :wq + Enter

Nano Text Editor

Nano is a newer and much easier text editor to navigate.
```
$ nano sample.txt
```
By default, Nano puts you directly into editing mode. It also displays a helpful list of commands at the bottom of the screen.
- Enter some text, then press Ctrl+O to save the changes.
- Press Ctrl+X to exit the editor.

Reading file content

cat

concatenate files and print on the standard output
```
$ cat sample.text
```

less

displays contents of a file, automatically fits to size of Terminal, allows scrolling in either direction and other options for effective viewing
```
$ less sample.txt
```

head

displays the first 10 lines of a text file by default
```
$ head sample.txt
```

tail

head command displays the last 10 lines of a text file by default
```
$ tail sample.txt
```

Copying and moving files

The cp command is used to copy files and directories
To copy a single file or directory, specify the source as first argument and destination as second argument

Similar to rm command, use -r for directories

$ # Two file names
$ # cp src_file dest_file
$ cp a.txt b.txt

$ # One or more arguments
$ # cp src_file1 src_file2 src_file3 dest_dir
$ cp a.txt b.txt new_folder

$ # Two directory names
$ # cp -r src_dir dest_dir
$ cp -r old_folder new_folder

The Secure Copy (scp) command can be used to transfer files from one machine to another. (It uses SSH under the hood.)
```
$ scp file_to_be_transferred.txt remote_username@0.0.0.0:/remote/directory/new_file_name.txt
```

More details

Renaming files

`mv` command

mv command is used to rename or move files from one location to another.
```
$ # mv [OPTIONS] source destination
$ mv file1.txt file2.txt
```

`rename` command

rename command in Linux is used to rename the named files according to the regular expression perlexpr.

It is not part of a standard Linux distribution, so you will need to install it.

$ # Install rename
sudo apt-get install rename

$ # Syntax
$ # rename [OPTIONS] perlexpr files
$ rename 's/.html/.php/' \*.html

The above example will change all files with the extension .html to .php

Deleting files & directories

This will permanently delete your files. They will not be found in the ‘Trash’ folder.
To delete files
```
$ rm samplefile.txt
```
To delete directories, use -r option
```
$ rm -r sampledir
```
To delete empty directories
```
$ rmdir sampledir
```

Chaining commands

You can chain multiple commands using &, &&, |, || and ; operators.

& Operator

$ command1 &

This will run command_1 in the background so that other commands can be executed.

&& Operator

$ command1 && command2

This will run will run command_1 and then run command_2 only if command_1 finished successfully.

| Operator

$ command1 | command2

The output of the command1 acts as input to command2.

|| Operator

$ command1 || command2

This will run will run command_1 and then run command_2 only if command_1 did not finish successfully.

; Operator

$ command1 ; command2

This will run will run command_1 and then run command_2 even if command_1 did not finish successfully.

Finding Strings and Counting Occurences

`grep`

Origin of grep

To find the occurence of a string, use grep "<string>" file_name.ext

$ grep "current" bank.lst
101 Aditya 0 14/11/2000 current
                        ^^^^^^^
103 Naman0 20/08/2009 current
                      ^^^^^^^

To count the occurence(s) of a string, use grep -c "<string>" file_name.ext
```
$ grep -c "current" bank.lst
2
```

To find the occurence(s) of a string with the line number, use grep -n "<string>" file_name.ext

$ grep -n "current" bank.lst
1:101 Aditya 0 14/11/2000 current
                          ^^^^^^^
3:103 Naman0 20/08/2009 current
                        ^^^^^^^

To find the occurence(s) of a line without the string, use grep -v "<string>" file_name.ext

$ grep -v "current" bank.lst
Chirag 0 15/12/2012 Current
Arya 16000 14/12/2010 Current
Priya 130 16/11/2009 Saving

To find files with the occurence of a string, use grep -l "<string>" *.ext
```
$ grep -l "current" *.lst
bank.lst
customers.lst
```
To find files without the occurence of a string, use grep -L "<string>" *.ext
```
$ grep -L "current" *.java
bnk.java
cust.java
```

To find lines from different files with a string (including the file names), use grep -H "<string>" *.ext

$ grep -H "current" *.lst
bank.lst:101 Aditya 0 14/11/2000 current
                                 ^^^^^^^
bank.lst:103 Naman0 20/08/2009 current
                               ^^^^^^^
clist.lst:101 Aditya 0 14/11/2000 current
                                  ^^^^^^^
clist.lst:103 Naman0 20/08/2009 current
                                ^^^^^^^
newbank.lst:101 Aditya 0 14/11/2000 current
                                    ^^^^^^^
newbank.lst:103 Naman0 20/08/2009 current
                                  ^^^^^^^

To find lines from different files with a string (without including the file names), use grep -h "<string>" *.ext

$ grep -h "current" *.lst
101 Aditya 0 14/11/2000 current
                        ^^^^^^^
103 Naman0 20/08/2009 current
                      ^^^^^^^
101 Aditya 0 14/11/2000 current
                        ^^^^^^^
103 Naman0 20/08/2009 current
                      ^^^^^^^
101 Aditya 0 14/11/2000 current
                        ^^^^^^^
103 Naman0 20/08/2009 current
                      ^^^^^^^

To find the occurence of a string while ignoring the case, use grep -i "<string>" file_name.ext

$ grep -i "current" bank.lst
101 Aditya 0 14/11/2000 current
                        ^^^^^^^
103 Naman0 20/08/2009 current
                      ^^^^^^^
106 Mukesh 14000 20/12/2009 Current
                            ^^^^^^^
108 Chirag 0 15/12/2012 Current
                        ^^^^^^^

To find the occurence of strings, use grep -e "<string_1>" -e "<string_2>" -e "<string_3>"... file_name.ext (Can be used to ignore case as well, by entering all the allowed strings.)

$ grep -e "current" -e "Mu" bank.lst
101 Aditya 0 14/11/2000 current
                        ^^^^^^^
103 Naman0 20/08/2009 current
                      ^^^^^^^
106 Mukesh 14000 20/12/2009 Current
    ^^

To find all lines with a string ignoring the case of a few characters, use:

$ grep "[Cc]urrent" bank.lst
101 Aditya 0 14/11/2000 current
                        ^^^^^^^
103 Naman0 20/08/2009 current
                      ^^^^^^^
106 Mukesh 14000 20/12/2009 Current
                            ^^^^^^^
108 Chirag 0 15/12/2012 Current
                        ^^^^^^^
109 Arya 16000 14/12/2010 Current
                          ^^^^^^^

To find a number of lines before and after a string, use grep -<number> "<string>" file_name.ext

$ grep -1 "current" bank.lst
101 Aditya 0 14/11/2000 current # The line above this is not printed as this is itself the first line in the file
                        ^^^^^^^
102 Anil 10000 20/05/2011 saving
103 Naman0 20/08/2009 current
                      ^^^^^^^
104 Ram 10000 15/08/2010 saving

To find all lines starting with a string, use grep "^<string>" file_name.ext
```
$ grep "^11" bank.lst
110 Priya 130 16/11/2009 Saving
^^
```

To find all lines starting within a string range, use grep "^[<string>-<string>]" file_name.ext

$ grep "^[1-2]" bank.lst
101 Aditya 0 14/11/2000 current
^
...

110 Priya 130 16/11/2009 Saving
^
201 Bina 3000 11/03/2010 saving
^
202 Diya 4000 13/04/2018 saving
^
203 Gargi 2000 21/01/2015 saving
^

To find all lines not starting with a string, use grep ^[^<string>] <file_name.ext> (The outer ^ is negating the pattern.)

$ grep "^[^1]" bank.lst
201 Bina 3000 11/03/2010 saving
^
202 Diya 4000 13/04/2018 saving
^
203 Gargi 2000 21/01/2015 saving
^

To find all lines not starting with a string in a range of characters, use grep ^[^<string>-<string>] <file_name.ext> (The outer ^ is negating the pattern.)
```
$ grep "^[^0-1]" bank.lst
201 Bina 3000 11/03/2010 saving
^
202 Diya 4000 13/04/2018 saving
^
203 Gargi 2000 21/01/2015 saving
^
```

To find all lines ending with a string, use grep "<string>$" file_name.ext

$ grep "nt$" bank.lst
101 Aditya 0 14/11/2000 current
                             ^^
103 Naman0 20/08/2009 current
                           ^^
106 Mukesh 14000 20/12/2009 Current
                                 ^^
108 Chirag 0 15/12/2012 Current
                             ^^
109 Arya 16000 14/12/2010 Current
                               ^^

To find all lines starting or ending with a string anywhere in the line and having a fixed number of characters after or before it respectively, use grep "...<string>" file_name.ext or grep "<string>..." file_name.ext (Every . indicates one character.)

$ grep "......nt" bank.lst
101 Aditya 0 14/11/2000 current
                        ^^^^^^^
103 Naman0 20/08/2009 current
                      ^^^^^^^
106 Mukesh 14000 20/12/2009 Current
                            ^^^^^^^
108 Chirag 0 15/12/2012 Current
                        ^^^^^^^
109 Arya 16000 14/12/2010 Current
                          ^^^^^^^

To find all lines starting and ending with a string and having a fixed number of characters in between, use grep "<string>...<string>" file_name.ext (Every . indicates one character.)

$ grep "Cur..nt" bank.lst
106 Mukesh 14000 20/12/2009 Current
                            ^^^^^^^
108 Chirag 0 15/12/2012 Current
                        ^^^^^^^
109 Arya 16000 14/12/2010 Current
                          ^^^^^^^

To find all lines starting and ending with a string and having any number of characters in between, use grep "<string>.*<string>" file_name.ext

$ grep "C.*nt" bank.lst
106 Mukesh 14000 20/12/2009 Current
                            ^^^^^^^
108 Chirag 0 15/12/2012 Current
                        ^^^^^^^
109 Arya 16000 14/12/2010 Current
                          ^^^^^^^

To find lines with strings stored in a file, use grep -f <pattern_file.ext> <target_file.ext>

$ cat pattern.txt
current
Saving
^d

$ grep -f pattern.txt bank.lst
101 Aditya 0 14/11/2000 current
                        ^^^^^^^
103 Naman0 20/08/2009 current
                      ^^^^^^^
110 Priya 130 16/11/2009 Saving
                         ^^^^^^

AWK

AWK is a programming language executed by the AWK interpreter.
The AWK language is a data-driven scripting language consisting of a set of actions to be taken against streams of textual data – either run directly on files or used as part of a pipeline – for purposes of extracting or transforming text, such as producing formatted reports.
It designed for text processing and typically used as a data extraction and reporting tool.
Like sed and grep, it is a filter, and is a standard feature of most Unix-like operating systems.
It is named after the three people who developed it, namely Alfred Aho, Peter Weinberger and Brian Kernighan.
General syntax for the AWK command: awk option '/pattern/ {action}' <file_name.ext>
- An AWK command must have a pattern, an action or both.
- Specifying an option is optional.
- If a pattern is not specified, it will be entire line.
- If an action is not specified, by default it is print.

Print all records of file

$ awk '{print}' bank.lst
Aditya 0 14/11/2000 current
Anil 10000 20/05/2011 saving
...
Priya 130 16/11/2009 Saving
Bina 3000 11/03/2010 saving
Diya 4000 13/04/2018 saving
Gargi 2000 21/01/2015 saving

Print first 3 fields (Fields indicated by: $<field_no>)

$ awk '{print $1 $2 $3}' bank.lst
101Aditya0
102Anil10000
...
110Priya130
201Bina3000
202Diya4000
203Gargi2000

Sepearate fields by tabs.

$ awk '{print $1 "\t" $2 "\t" $3}' bank.lst
   Aditya  0
   Anil    10000
...
   Priya   130
   Bina    3000
   Diya    4000
   Gargi   2000

Format specifiers

$ awk '{printf "%3d \t %7s \t %5d\n", $1, $2, $3}' bank.lst
     Aditya             0
       Anil         10000
...
      Priya           130
       Bina          3000
       Diya          4000
      Gargi          2000

Print only those records having a pattern.

$ awk '/current/ {print}' bank.lst
101 Aditya 0 14/11/2000 current
103 Naman 0 20/08/2009 current

# OR

$ awk '/current/ {print $0}' bank.lst  # '$0' means the entire line
101 Aditya 0 14/11/2000 current
103 Naman 0 20/08/2009 current

Print records based on mathematical conditions

$ awk '$3 < 5000 {print $1 "\t" $2 "\t" $3}' bank.lst
   Aditya  0
   Naman   0
   Chirag  0
   Priya   130
   Bina    3000
   Diya    4000
   Gargi   2000

$ awk '$3 > 3000 && $3 < 8000 {print $1 "\t" $2 "\t" $3}' bank.lst  # '||' is logical OR
   Jyotsna 5000
   Diya    4000

Print records if a field matches a certain string/pattern or not.

$ awk '$5 == "current"' bank.lst  # OR awk '$5 ~/current/' bank.lst
Aditya 0 14/11/2000 current
Naman 0 20/08/2009 current

$ awk '$5 != "current"' bank.lst  # OR awk '$5 !~/current/' bank.lst
Anil 10000 20/05/2011 saving
Ram 10000 15/08/2010 saving
...
Priya 130 16/11/2009 Saving
Bina 3000 11/03/2010 saving
Diya 4000 13/04/2018 saving
Gargi 2000 21/01/2015 saving

Print records with a field ending or not ending with a string/pattern.

$ awk '$5 ~/nt$/' bank.lst
Aditya 0 14/11/2000 current
Naman 0 20/08/2009 current
Mukesh 14000 20/12/2009 Current
Chirag 0 15/12/2012 Current
Arya 16000 14/12/2010 Current

$ awk '$5 !~/nt$/' bank.lst
Anil 10000 20/05/2011 saving
Ram 10000 15/08/2010 saving
Jyotsna 5000 16/06/2012 saving
Vishal 14500 30/11/2011 saving
Priya 130 16/11/2009 Saving
Bina 3000 11/03/2010 saving
Diya 4000 13/04/2018 saving
Gargi 2000 21/01/2015 saving

Print records with a field value, while ignoring the case.

$ awk '$5 ~/[Cc]urrent/' bank.lst
Aditya 0 14/11/2000 current
Naman 0 20/08/2009 current
Mukesh 14000 20/12/2009 Current
Chirag 0 15/12/2012 Current
Arya 16000 14/12/2010 Current

Built-in AWK variables
- https://www.thegeekstuff.com/2010/01/8-powerful-awk-built-in-variables-fs-ofs-rs-ors-nr-nf-filename-fnr/
- https://www.linuxnix.com/awk-scripting-learn-awk-built-in-variables-with-examples/

Print record numbers 4 to 6.

$ awk 'NR > 3 && NR < 7 {print $1 "\t" $2}' bank.lst
   Ram
   Jyotsna
   Mukesh

$ awk 'NR == 4, NR == 6 {print $1 "\t" $2}' bank.lst
   Ram
   Jyotsna
   Mukesh

Unix/Linux Terminal

Opening the Terminal

Linux

MacOS

Windows

Keyboard shortcuts

File System

Absolute and Relative Paths

Basics of Linux/Unix Commands

Command Structure

Command Help

Variables

Basic Commands

Print name of cwd (current working directory)

Clear screen & command history

Changing directories

Package manager

Check for package updates

Install a package

Remove a package

Run files on cmd

Listing directory contents & directory structure

Changing Permissions

Further Reading:

Creating directories

Creating files

touch command

Redirect operator (>)

cat command

echo command

Using text editors

Redirecting output

Redirect to a file

Redirect to another command

Editing a file

Vi Text Editor

Vim Text Editor

Nano Text Editor

Further Reading:

Reading file content

cat

less

head

tail

Copying and moving files

Renaming files

mv command

rename command

Further Reading:

Deleting files & directories

Chaining commands

& Operator

&& Operator

| Operator

|| Operator

; Operator

Finding Strings and Counting Occurences

grep

AWK

`touch` command

`cat` command

`echo` command

`mv` command

`rename` command

`grep`