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# awk(1)
```markdown
awk [opt] program [input]
-F <sepstr> field separator string (can be regex)
program awk program
input file or stdin if not file given
```
## Input processing
Input is processed in two stages:
1. Splitting input into a sequence of `records`.
By default split at `newline` character, but can be changed via the
builtin `RS` variable.
2. Splitting a `record` into `fields`. By default strings without `whitespace`,
but can be changed via the builtin variable `FS` or command line option
`-F`.
Field are accessed as follows:
- `$0` whole `record`
- `$1` field one
- `$2` field two
- ...
## Program
An `awk` program is composed of pairs of the form:
```markdown
pattern { action }
```
The program is run against each `record` in the input stream. If a `pattern`
matches a `record` the corresponding `action` is executed and can access the
`fields`.
```markdown
INPUT
|
v
record ----> ∀ pattern matched
| |
v v
fields ----> run associated action
```
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