{"id":32407,"date":"2022-12-23T06:03:44","date_gmt":"2022-12-23T06:03:44","guid":{"rendered":"https:\/\/www.devopsschool.com\/blog\/?p=32407"},"modified":"2022-12-23T06:12:04","modified_gmt":"2022-12-23T06:12:04","slug":"shell-scripting-tutorials-looping-iteration-statatement-using-while","status":"publish","type":"post","link":"https:\/\/www.devopsschool.com\/blog\/shell-scripting-tutorials-looping-iteration-statatement-using-while\/","title":{"rendered":"Shell Scripting Tutorials: Looping & Iteration statatement using while"},"content":{"rendered":"\n
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The bash while loop is a control flow statement that allows code or commands to be executed repeatedly based on a given condition.<\/p>\n\n\n\n

Most languages have the concept of loops: If we want to repeat a task twenty times, we don’t want to have to type in the code twenty times, with maybe a slight change each time.
As a result, we have for and while loops in the Bourne shell.<\/p>\n\n\n\n

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Types of Loops in Shell Scripting<\/h2>\n\n\n\n
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\"\"<\/figure>\n\n\n\n
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Syntax of Shell Scripting<\/h2>\n\n\n\n
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\"\"<\/figure>\n\n\n\n
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Control Flow of While Loop<\/h2>\n\n\n\n
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Example of While Loop in Shell Script<\/h2>\n\n\n\n
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\"\"<\/figure>\n\n\n\n
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Boolean Operators When Working With Shell Scripts<\/h2>\n\n\n\n
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Apart from the boolean operators that you\u2019ve seen in other programming languages, including ==, <, >, <=, >=,<\/strong> etc., these are shell script specific operators. The major usage difference is that these operators will only work when numeric values<\/strong> are provided. With string value, the operation will simply fail.<\/p>\n\n\n\n

Operator<\/th>Description<\/th>Example<\/th><\/tr>
-ne<\/td>Checks if both operands are not equal<\/td>[ 1 -ne 2 ] is TRUE<\/td><\/tr>
\u2013<\/strong>eq<\/td>Checks if both the operands are equal<\/td>[ 1 -eq 2 ] is FALSE<\/td><\/tr>
\u2013<\/strong>lt<\/td>Check if the left operand is lesser than the right operand<\/td>[1-lt 2 ] is TRUE<\/td><\/tr>
\u2013<\/strong>gt<\/td>Check if the left operand is greater than the right operand<\/td>[1-gt 2 ] is FALSE<\/td><\/tr>
\u2013<\/strong>le<\/td>Check if the left operand is less than or equal to the right.<\/td>[1-le 2 ] is TRUE<\/td><\/tr>
\u2013<\/strong>ge<\/td>Check if the left operand is greater than or equal to the right.<\/td>[1-ge 2 ] is FALSE<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Creating a While Loop in Shell Script<\/h2>\n\n\n\n

A while loop doesn\u2019t have a repetition limit by default. We have to explicitly provide it a condition that at some point during the code execution, will turn to false. Else you\u2019ll have a loop that doesn\u2019t end unless an interrupt signal is sent.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Save the script above by any name with the .sh<\/strong> extension. To run the file, you can either run it with the bash command like bash <filename>.sh<\/strong> or make the file executable using the chmod command. To make the script executable, run chmod +x <filename>.sh<\/strong> and then .\/<filename>.sh<\/strong> will allow you to run the script.<\/p>\n\n\n\n

Let\u2019s understand the script line by line.<\/strong><\/p>\n\n\n\n