71 lines
1.1 KiB
Markdown
71 lines
1.1 KiB
Markdown
---
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tags:
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- shell
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---
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# Loops in Bash
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## Traditional for loop
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```bash
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for (( i=0; i<=5;i++ )); do
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echo $i
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done
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# 1 2 3 4 5
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```
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## `for..in`: loop through an array
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```bash
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for element in "${arr[@]}"
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do
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echo "$element"
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done
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```
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## While loop
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> `while` loops execute while a condition is true (0)
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We can use a `while` loop as a condition in two senses:
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- execute while a given condition obtains
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- expand and execute a given command as long as the final command in the `while'
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for the command has an exit status of zero (i.e. truthy)
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Here is an exampe of using `while` in the former case:
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```sh
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declare -i n=0
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while (( n<10 ))
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do
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echo "n:$n"
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(( n++ ))
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done
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```
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Here is an example of using `while` in the latter case:
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```sh
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while read line;
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do
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# something
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done < "$file_to_read"
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```
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## Until loop
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> `until` loops execute until a condition is false (1)
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```sh
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declare -i m=0
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until (( m==10 )): do
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echo "m:$m"
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(( m++ ))
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done
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```
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This gives us the same output as `n` with the while loop but here it runs so
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long as `m==10` is false. As soon as `m` is equal to 100, the condition becomes
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true and hence the loop stops.
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