Beginner Guide Using Bash

What is Bash? is a command-line interpreter that lets you interact with your UNIX or Apple OS.

Bash is useful for navigating into your system, run programs and automate tasks. For many environments—especially remote servers accessed via SSH—Bash is the main way to interact with the system, since there’s no graphical interface (GUI).

Basic Bash Commands

Let’s list some of the most common commands you’ll use almost every day

Basic Navigation Commands

pwd      # Show current directory
ls       # List files
cd       # Change directory
cd ..    # Go up one level
cd ~     # Go to home directory
cd -     # Go to the previous directory

Example

cd /var/log

pwd
# /var/log

cd ..
# /var

ls
# apache.log wifi.log system.log

Working with Files & Folders

mkdir project        # Create folder
touch app.py         # Create file
cp file.txt copy.txt # Copy file
mv file.txt new.txt  # Move/rename
rm file.txt          # Delete file
rm -r folder/        # Delete folder

Example

mkdir project
touch app.py
mv app.py project/app.py
rm project/app.py or rm -r project #to remove both folder and file

⚠️ Be very careful with rm — there is no undo.

What is sudo? sudo (superuser do) allows you to run commands with administrator privileges. In simple terms, it removes most safety restrictions.

That’s why sudo rm -r is so dangerous — it can delete anything on the system without asking twice and it will be "Game Over".

Viewing File Content

cat file.txt     # Show full content
less file.txt    # Scroll through file
head file.txt    # First lines
tail file.txt    # Last lines
tail -f app.log  # Follow live updates of file content

Example

cat file.txt
# This File is a test file

Searching

grep "error" app.log # find lines inside the file containing the work "error"
find . -name "*.log" # find files by name

Permissions

chmod +x script.sh #Makes the script executable

Combining Commands

cat file.txt | grep "error" # take the output of one command and pass it to another
echo "This is a test" >> file.txt # append to file
echo "This is a test" > file.txt  # overwrite file

Simple Scripting

touch script.sh
chmod +x script.sh
vim script.sh or nano script.sh

Inside the file with your favorite text editor

#!/bin/bash

# printing this sentence in the terminal. Why not?
echo "Lets write my first script"

#Create a file
touch file.txt

#Insert the text inside the file
echo "I created this file" > file.txt

#Show the context of the file
cat file.txt

Execute the script

./script.sh

Output

Lets write my first script
I created this file

Tips

• Every command has options (arguments) that change its behavior.
• Every argument is useful, it will depend on the situation or what you are trying to accomplish with it.
• You can read the manual for any command:

man ls

NAME
     ls – list directory contents

SYNOPSIS
     ls [-@ABCFGHILOPRSTUWabcdefghiklmnopqrstuvwxy1%,] [--color=when] [-D format] [file ...]

DESCRIPTION
     For each operand that names a file of a type other than directory, ls displays its name as well as any requested, associated information.  For each operand
     that names a file of type directory, ls displays the names of files contained within that directory, as well as any requested, associated information.

     If no operands are given, the contents of the current directory are displayed.  If more than one operand is given, non-directory operands are displayed
     first; directory and non-directory operands are sorted separately and in lexicographical order.

     The following options are available:

     -@      Display extended attribute keys and sizes in long (-l) output.

     -A      Include directory entries whose names begin with a dot (‘.’) except for . and ...  Automatically set for the super-user unless -I is specified.

     -B      Force printing of non-printable characters (as defined by ctype(3) and current locale settings) in file names as \xxx, where xxx is the numeric
             value of the character in octal.  This option is not defined in IEEE Std 1003.1-2008 (“POSIX.1”).

     -C      Force multi-column output; this is the default when output is to a terminal.

     -D format
             When printing in the long (-l) format, use format to format the date and time output.  The argument format is a string used by strftime(3).
             Depending on the choice of format string, this may result in a different number of columns in the output.  This option overrides the -T option.
             This option is not defined in IEEE Std 1003.1-2008 (“POSIX.1”).

     -F      Display a slash (‘/’) immediately after each pathname that is a directory, an asterisk (‘*’) after each that is executable, an at sign (‘@’) after
             each symbolic link, an equals sign (‘=’) after each socket, a percent sign (‘%’) after each whiteout, and a vertical bar (‘|’) after each that is a
             FIFO.
man cat

NAME
     cat – concatenate and print files

SYNOPSIS
     cat [-belnstuv] [file ...]

DESCRIPTION
     The cat utility reads files sequentially, writing them to the standard output.  The file operands are processed in command-line order.  If file is a single
     dash (‘-’) or absent, cat reads from the standard input.  If file is a UNIX domain socket, cat connects to it and then reads it until EOF.  This complements
     the UNIX domain binding capability available in inetd(8).

     The options are as follows:

     -b      Number the non-blank output lines, starting at 1.

     -e      Display non-printing characters (see the -v option), and display a dollar sign (‘$’) at the end of each line.

     -l      Set an exclusive advisory lock on the standard output file descriptor.  This lock is set using fcntl(2) with the F_SETLKW command.  If the output
             file is already locked, cat will block until the lock is acquired.

     -n      Number the output lines, starting at 1.

     -s      Squeeze multiple adjacent empty lines, causing the output to be single spaced.

     -t      Display non-printing characters (see the -v option), and display tab characters as ‘^I’.

     -u      Disable output buffering.

     -v      Display non-printing characters so they are visible.  Control characters print as ‘^X’ for control-X; the delete character (octal 0177) prints as
             ‘^?’.  Non-ASCII characters (with the high bit set) are printed as ‘M-’ (for meta) followed by the character for the low 7 bits.

Practice makes perfect. Don’t try to learn everything at once—with time, it will feel natural.

For more information about bash and editing files check this post.