Characteristic features
All environmental variables are imported into the context.
Command construction, execution
Very simple syntax for execution of commands: simply use a line which says: commandName. Construction of command-strings using variable names is also simple: someText $varName otherText
Logic limitations
Not suitable for logic more involved than an if else statement.
Writing and executing code
Bash commands and programs can either be run by providing/ typing the program in STDIN, or it can be run from a file.
Context
Every sequence of Bash commands is executed in a certain context. Different contexts do not share the variables (including environment variables like PWD and PATH) - so changing variables in one context does not affect another.
Current context
source fileName executes the file in the current context.
New context
One can run a file using: bash fileName.
Invocation as a command
One can execute the file merely by saying fileName at the command prompt, if it begins with: #!/usr/bin/bash . This line is used by many interpreters to identify and use the interpreter appropriate to the file when one runs the file.
If #!/usr/bin/bash -x is used, all executed lines are echoed.
Environment variables
Some variables, called the environment variables, are set automatically when a shell context is created.
These variables are important because they are used while searching for various purposes affecting terminal display and command interpretation/ execution. Eg: \verb LD_LIBRARY_PATH , PATH (a : separated list of directories where an executable file is to be sought), PWD (present working directory).
Setting
export VAR=value sets an environment variable.
To set these at startup, edit .bashrc and \verb .bash_aliases in the home directory. env lists the environment variables.
Variables and data
Dynamic typing.
Assignment
VARNAME=value. Array: area2=( zero one two three four ) A particular element is set with area2[0]=val
Note that there should not be any space around =.
Reference
\verb|$VAR_NAME ${VAR_NAME}| are references to the variable.
Array Element reference: ${area2[0]}.
Reference the entire array: ${colors[@]}.