lk/system/awk.md
Malin Freeborn ba8026e0c3
change formatting
input examples are now given as

```bash
input $ARG1
```

While outputs use md's '> ' sign as a quote.
2023-06-17 21:28:20 +02:00

90 lines
1.5 KiB
Markdown

---
title: "awk"
tags: [ "Documentation", "System" ]
---
# Basics
See a file's contents:
Return full contents of a string:
```bash
awk '{ print }' file
```
Print the first and second column:
```bash
awk '{print$1$2}'
```
Return every line with the word 'the' (like grep):
```bash
awk '/the/{print}' file
```
Print everything containing a lowercase letter:
```bash
awk '/[a-z]/{print}' file
```
Same with numbers [0-9], or using a caret we can show lines starting with a number - ^[0-9], or ending with an uppercase letter - $[A-Z].
# Conditionals
```bash
awk '{ if($1 ~ /123/) print }' file
```
Check if the first column is equal to 1 or 2 or 3, and if so then print that line.
Grep for 'hawk' in a story:
```bash
awk '/hawk/' story.txt
```
Return any line with one or more "&" sequences:
```bash
awk '/&+/' script.sh
```
The pipe is used for 'or', so 'Orcs or drums' would be:
```bash
awk '/Orcs|Drums/' story.txt
```
Basic variables are:
- FS = Input field separator
- OFS = Output field separator
- NF = Number of fields on the current line
- NR = Number of records in the current file
- RS = Record separator
- ORS = Output record separator
- FILENAME = the file you're looking at.
So you can count the number of lines in a file, by referencing the number of 'end line' statements:
> awk 'END{print NR}' story.txt
Print line 2 from story.txt
> awk '{if(NR~/^2$/)print}' story.txt
Same, but any line starting with "2":
> awk '{if(NR~/^2/)print}' story.txt