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Bash

Introduction​

This page documents bash syntax that I've learned.

Define variables​

In Bash, you can define a variable by using the following syntax:

variable_name=value
# Example:
name="John"
note

There should be no spaces around the equals (=) sign.

Variables in Bash are not typed, so you don't need to specify the data type. They can hold strings, numbers, or any other type of data.

echo variables​

To access the value of a variable, you can use the variable name preceded by the dollar sign ($):

echo $name

You can also assign the output of a command to a variable using command substitution:

current_date=$(date)

In this example, the output of the date command is assigned to the current_date variable.

export variables​

Variables in Bash are by default local to the current shell or script. If you want to export a variable to be accessible by other scripts or programs, you can use the export command:

export MY_VARIABLE_1
export MY_VARIABLE="Hello, World!"

It can then be imported. For an example of how a Bash variable is imported and used in a Python script, see Importing Bash Variables.

if statement​

if [[ "$fname" == "a.txt" || "$fname" == "c.txt" ]]; then 
  echo Hello # a command to run if the condition is met
fi

More info:

  • ==: if $fname equals to a.txt or c txt
  • \\: True if either expression1 or expression2 is true.
  • &&: True if both expression1 and expression2 are true.