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42 lines
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1.3 KiB
Markdown
42 lines
No EOL
1.3 KiB
Markdown
---
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date: 2022-06-19 18:49:47-04:00
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draft: false
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math: false
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medium_enabled: true
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medium_post_id: 8217bfd3af16
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tags:
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- Bash
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title: Conditional Assignment in Bash
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---
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Many programming languages include an quick way to perform a
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conditional assignment. That is, assigning a variable with a value
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based on some condition. Normally this is done through a ternary
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operator. For example, here is how to write it in Javascript
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```javascript
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age = 16;
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ageType = (age > 18) "Adult": "Child";
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```
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The variable `ageType` is dependent upon the value of `age`. If it is above 18 then `ageType = "Adult"` otherwise `ageType = "Child"`.
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A more verbose way of accomplishing the same thing is the following:
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```javascript
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if (age > 18) {
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ageType = "Adult"
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} else {
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ageType = "Child"
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}
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```
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How do we do conditional assignment in Bash? One way is to make use of subshells and echoing out the values.
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```bash
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AGE_TYPE=$([ $AGE -gt 18 ] && echo "Adult" || echo "Child")
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```
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A common programming feature called *short-circuiting* makes it
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so that if the first condition (`[ $AGE -gt 18 ]`) is false, then it
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will skip the right side of the AND (`&&`) expression. This is because
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`False && True` is always `False`. However, `False || True` is equal
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to `True`, so the language needs to evaluate the right part of an
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OR (`||`) expression. |