104 lines
1.5 KiB
Markdown
104 lines
1.5 KiB
Markdown
---
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categories:
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- Programming Languages
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tags:
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- shell
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---
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# Splitting input into an array
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## readarray
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`readarray` makes it really easy to split input into an array based on new
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lines. Say we have this file as input:
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```
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123
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456
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789
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```
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Then we can split like so:
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```bash
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readarray -t name_for_array < ./input.text
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# Print all elements
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echo "${name_for_array[@]}"
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# Print element by index
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echo "${name_for_array[1]}"
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456
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```
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If we want to read a string directly:
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```bash
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readarray -t new_name_for_array <<< "here
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is
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some
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text"
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echo "${new_name_for_array[1]}"
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is
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```
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> The _-t_ flag removes the trailing newline
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See more: https://linuxhint.com/split-string-array-bash/
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## read
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For delimiters other than a space we have to use `read`, combined with `IFS` the
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**Internal Field Separator**.
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For example, to split by comma:
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```plaintext
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# comma-input.txt
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something,something else,something more
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```
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```bash
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IFS=',' read -a arr < ./comma_inputs.txt
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```
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> We use the `-a` flag to signal that we want each item read returned as an
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> element in an array
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## mapfile
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We can use `mapfile` to read the lines of a input file in set segments.
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For the following file:
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```
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line one
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line two
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line three
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line four
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```
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We could generate the following output:
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```
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-----SNIP-----
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line one
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line two
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-----SNIP-----
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line three
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line four
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```
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With:
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```bash
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while mapfile -t -n 2 ary && ((${#ary[@]})); do
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printf '%s\n' "${ary[@]}"
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printf -- '--- SNIP ---\n'
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done < $testInput
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```
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So, while there are input lines, map each line into an array and return it in
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groups of 2.
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