Shell Scripting

echo

it is the Bash Shell output mechanism:

echo

prints arguments to standard output separated by spaces

Prints the text you give it, then moves the cursor to the next line.

echo -n argument

no trailing newline after output

Prints the text but keeps the cursor on the same line. It Negates the automatic newline.

echo -e argument

interpret \char escapes

It tells echo to Enable the interpretation of special codes (called "escape sequences") that start with a backslash (\).

echo -E argument

do not interpret \char escapes

Explicitly tells echo to not interpret the escape sequences; it prints them Exactly as they are.

\a Alarm

ring the terminal bell

\b

Backspace

\c

print without trailing newline (same as print -n)

\f

Form feed

\n

Newline

\r

Return

\t

tab

\v

vertical tab

\\

Backslash

\xxx

Character with octal code (up to three octal digits)

read

To get input while a Shell Script is running

allows you to prompt for input and store it in a variable.

shell script or shell program

Shell program interprets user commands, which are either directly entered by the user, or which can be read from a file called

interpreted

Shell scripts are _______, not compiled

shell scripts

reads commands from the script line per line and searches for those commands on the system while a compiler converts a program into machine readable form, an executable file – which may then be used in a shell script.

#!/bin/bash

this an optional comment use to indicate will interpret by the bash shell.

echo

command displays the string, variables or arguments form the parameters.

sleep

command serves as a delay or pause for the next instructions or commands. [delay in seconds]

let argument

a built-in Shell command performs long integer arithmetic

let argument

approximately 10 times faster than expr

Evaluates each argument as an arithmetic expression

No quotes for special characters, or arguments with spaces or tabs

bc -

performs floating point arithmetic

acts as a filter command or interactively

reads arithmetic expression strings from standard input or specified file

semicolons or new lines separate expressions

set the scale variable inside bc to define the required number of decimal places

$

Variables need no 

0 (True)

The command completed without errors.

1 (False)

The command encountered an error (e.g., file not found, bad permissions, wrong syntax, general error).

compiler

converts a program into a machine-readable, executable file.

user environment

main task of a shell is providing this, and it can be configured individually using shell resource configuration files.

bc -l

a shell script to compute a discount, which involves division and decimals

ensures that the bc program is ready for precise floating-point math, handling the division correctly even if the numbers were more complex