echo is used to print the contents of a variable or a string.
echo "Hello World"
printf is used to print the contents of a variable or a string.
printf "Hello World"
Uses of read read is used to read the contents of a variable or a string.
read -p "Enter your name: " name
echo "Hello $name"
cat is used to print the contents of a file.
cat README.md
tr is used to translate the contents of a file.
tr 'a-z' 'A-Z' < README.md
paste is used to print the contents of a file.
paste README.md
if else statements are used to execute a block of code if a certain condition is true.
if [ $a -gt $b ]; then
echo "a is greater than b"
else
echo "a is not greater than b"
fi
for loops are used to iterate over a list of values. Say we have a list of numbers, we can use a for loop to iterate over the list and print each number.
for i in {1..10}
do
echo "Number is $i"
done
while loops are used to execute a block of code as long as a certain condition is true.
while [ $a -lt 10 ]
do
echo "Number is $a"
a=`expr $a + 1`
done
until loops are used to execute a block of code as long as a certain condition is false. until [ $a -gt 10 ]
until [ $a -gt 10 ]
do
echo "Number is $a"
a=`expr $a + 1`
done
case statements are used to execute a block of code based on the value of a variable.
case $a in
1) echo "a is 1";;
2) echo "a is 2";;
3) echo "a is 3";;
4) echo "a is 4";;
5) echo "a is 5";;
6) echo "a is 6";;
7) echo "a is 7";;
8) echo "a is 8";;
9) echo "a is 9";;
10) echo "a is 10";;
*) echo "a is not between 1 and 10";;
esac
Functions are used to group a block of code together and to reuse the code.
function myfunc() {
echo "Hello World"
}
myfunc
array=(1 2 3 4 5 6 7 8 9 10)
echo ${array[0]}
echo ${array[1]}
echo ${array[2]}
echo ${array[3]}
echo ${array[4]}
echo ${array[5]}
echo ${array[6]}
echo ${array[7]}
echo ${array[8]}
echo ${array[9]}
Associative arrays are used to store key value pairs.The key is the index and the value is the value.
declare -A assoc_array
assoc_array[key1]=value1
assoc_array[key2]=value2
assoc_array[key3]=value3
echo ${assoc_array[key1]}
echo ${assoc_array[key2]}
echo ${assoc_array[key3]}
Functions are used to group a block of code together and to reuse the code.
function myfunc() {
echo "Hello World"
}
myfunc
Head is used to print the first n lines of a file.
```
head -n 5 README.md
```
Tail is used to print the last n lines of a file.
```
tail -n 5 README.md
```
grep is used to search for a pattern in a file.
grep "Hello" README.md
cut is used to extract a specific field from a file.
cut -d " " -f 1 README.md
sort is used to sort a file.
sort -n README.md
uniq is used to remove duplicate lines from a file.
uniq README.md
wc is used to count the number of lines, words and characters in a file.
wc README.md
tr is used to translate characters in a file.
tr " " "-" README.md
sed is used to edit a file.
sed "s/Hello/Hi/g" README.md
Data Types:
| Type | Description | Example | Size(bytes) |
|---|---|---|---|
| String | A string is a sequence of characters. | "Hello World" | 11 |
| Integer | An integer is a number without decimal points. | 123 | 4 |
| Float | A float is a number with decimal points. | 1.23 | 4 |
| Boolean | A boolean is a true or false value. | true | 1 |
| Array | An array is a list of values. | [1, 2, 3, 4, 5] | 5 |
| Associative Array | An associative array is a list of key value pairs. | {"key1": "value1", "key2": "value2"} | 2 |
| Function | A function is a block of code that can be called. | function myfunc() { echo "Hello World"; } | 1 |
Example:
int=123
float=1.23
printf "Integer: %d\n" $int
printf "Float: %f\n" $float
In Bash, arithmetic operators are used to perform mathematical operations on numbers. Here are some of the most common arithmetic operators in Bash:
| Operator | Description | Example |
|---|---|---|
+ |
Addition | echo $((2 + 3)) |
- |
Subtraction | echo $((5 - 2)) |
* |
Multiplication | echo $((2 * 3)) |
/ |
Division | echo $((6 / 2)) |
% |
Modulus | echo $((7 % 3)) |
++ |
Increment | x=5; echo $((x++)) |
-- |
Decrement | x=5; echo $((x--)) |
Note that arithmetic operators are usually used in conjunction with the $(( )) syntax to evaluate the expression as a mathematical operation. For example:
In Bash, backslash escape sequences are used to insert special characters into strings. Here are some of the most common backslash escape sequences in Bash:
| Sequence | Description | Example |
|---|---|---|
\n |
Newline | echo -e "Hello\nworld" |
\t |
Tab | echo -e "Name\tAge" |
\\ |
Backslash | echo "This is a backslash: \\" |
\" |
Double quote | echo "She said, \"Hello.\"" |
\$ |
Dollar sign | echo "The price is \$10." |
Note that backslash escape sequences are usually used in conjunction with the -e option in the echo command to interpret the escape sequences. For example:
| Option | Description |
|---|---|
-a |
Show hidden files and directories |
-l |
List files in long format |
-h |
When used with -l, display file sizes in human-readable format |
-r |
Reverse the order of the list |
-t |
Sort the list by modification time |
-S |
Sort the list by file size |
-R |
List subdirectories recursively |
-G |
Colorize the output |
-1 |
Display each file on a separate line |
declare is used to create a variable.
declare -i int
declare -f func
declare -a array
declare -A assoc_array
Type of shell :
- Bash
- Zsh
Them are both interpreted by the shell and executed by the shell. The difference is that the Bash shell is a shell that is written in the Bourne Again Shell (BASH) language, while the Zsh shell is a shell that is written in the Zsh language. The Bash shell is the default shell on most UNIX systems, while the Zsh shell is the default shell on most UNIX systems.
We show here shell scripting in the following example or bash programming. However, the same can be done in the Zsh shell. Window command prompt has also has the programming language feature. You can use loops, if else statements, functions, arrays, associative arrays, and more. Its call batch scripting.