Shell Scripting Essentials
Different shells are available for Unix, Unix-like, or Linux OS
- Bourne shell (sh)
- C shell (csh)
- Korn shell (ksh)
- Bourne again shell (bash)
- Z shell (zsh)
We can use a Shebang to indicate and interpreter for execution:
#! /bin/bashTo run a shell script, make sure it has execute permission:
$ chmod u+x your-fileThe Beginning of the Scripting Journey
Hello World in shell
We can use printf command as in C language, using the format that we need and the arguments as follow:
- Using numbers and floating point
$ printf "%d multiply %f = %f \n" 6 6.0 36.0
6 mul 6.000000 = 36.000000- Using string
$ printf "%s Scripting \n" Shell
Shell ScriptingLet's make it scripted
We can create a script file called math.sh
#! /bin/bash
# Filename: math.sh
# Description: echo and printf to format texts
echo "Basic Math"
printf "%-7d %-7s %-7.2f =\t%-7.2f\n" 23 plus 5.5 28.5
printf "%-7.2f %-7s %-7d =\t%-7.2f\n" 50.50 minus 20 30.50
printf "%-7d %-7s %-7d =\t%-7d\n" 10 mul 5 50
printf "%-7d %-7s %-7d =\t%-7.2f\n" 27 div 4 6.75Will result:
Basic Math
23 plus 5.50 = 28.50
50.50 minus 20 = 30.50
10 mul 5 = 50
27 div 4 = 6.75Defining variables of choice
- A variable name can be a combination of alphanumeric and underscore
- Can't start with a number
- Are case sensitive
- Special characters, such as *, -, +, ~, ., ^, and so on, are not used in variable names because they have a special meaning in shell
Creating the following file
#! /bin/bash
# Filename: variables.sh
# Description: Using variables
book="Learning Spark"
book_description="Learning Spark in an easy way"
book_number_pages=300
echo "Learning Spark from book: $book"
echo "Description book: $book_description"
echo "Pages to be read: $book_number_pages"Will result
Learning Spark from book: Learning Spark
Description book: Learning Spark in an easy way
Pages to be read: 300
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