lk/system/awk.md
2022-01-26 23:35:07 +01:00

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