Bash
====


Bash
----

Shebang
^^^^^^^

The shebang line tells the system which interpreter to use to execute the script:

.. code-block:: bash

   #!/bin/bash

Variables
^^^^^^^^^^^^^^

Define and use variables:

.. code-block:: bash

   name="Bob"
   echo "Hello world, $name!"

User input
^^^^^^^

Read user input:

.. code-block:: bash

   echo "What is your name?"
   read name
   echo "Hello, $name!"

For loop
--------

Iterate through a range:

.. code-block:: bash

   for i in {1..5}; do
       echo "Number $i"
   done

Conditional statements
^^^^^^^

Use conditional logic:

.. code-block:: bash

   echo "Enter a number:"
   read num
   if [ $num -lt 10 ]; then
       echo "The number is less than 10."
   else
       echo "The number is 10 or greater."
   fi

Comparison operators:

- ``-lt`` for "less than"
- ``-gt`` for "greater than"
- ``-eq`` for "equals"
- ``-ne`` for "not equal"
- ``-le`` for "less than or equal to"
- ``-ge`` for "greater than or equal to"

While loop
^^^^^^^

Loop while a condition is true:

.. code-block:: bash

   counter=1
   while [ $counter -le 5 ]; do
       echo "Counter is $counter"
       ((counter++))
   done

Functions
---------

Define and call functions:

.. code-block:: bash

   intro() {
       echo "Hi $1! You are $2 years old."
   }
   intro "Bob" 30

Folder and file management
---------------------------


Loop through directories with argument validation:

.. code-block:: bash

   # $# is a special variable giving the number of arguments
   if [ "$#" -ne 1 ]; then
       echo "Usage: $0 /path/to/directory"
       exit 1
   fi

   # Use the first argument as the root directory
   root_dir="$1/*"

   # Loop through each item in the root directory
   for dir in $root_dir; do
       if [ -d "$dir" ]; then  # Check if it's a directory
           echo "Visiting directory: $dir"
           # Perform operations in "$dir"
       fi
   done

To use, run:

.. code-block:: bash

   ./script.sh /path/to/directory

Verify a file exists before proceeding:

.. code-block:: bash

   # Check if a file exists
   if [ ! -f "my_file.txt" ]; then
       echo "Error: File does not exist."
       exit 1
   fi

.. note::

   ``exit 1`` (or any non-zero value) indicates that the script terminated with an error. A successful script should ``exit 0`` or simply exit without a code.

Common file test operators
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

- ``-f file`` - True if file exists and is a regular file
- ``-d dir`` - True if dir exists and is a directory
- ``-e path`` - True if path exists (file or directory)
- ``-r file`` - True if file exists and is readable
- ``-w file`` - True if file exists and is writable
- ``-x file`` - True if file exists and is executable