A One‑Minute Guide to AWK: Basics, Syntax, and Common Use Cases

1. AWK AWK is named after its three creators – Aho, Weinberger, and Kernighan – and is a line‑oriented text‑processing tool commonly used in Unix environments.

2. Basic Principle The core idea of AWK is to process input files one line at a time. Its syntax follows the pattern + {action} model, where a pattern selects lines and the action defines what to do with them.

Example to display lines 3 to 5 of hello.txt : cat hello.txt | awk 'NR==3, NR==5{print;}'

2.3 Pattern Explanation Patterns can be regular expressions (e.g., /hello/ ) or numeric conditions. If no action is provided, the default action is print .

Example to print lines matching the word “hello”: cat hello.txt | awk '/hello/'

3. Built‑in Variables Common variables include: FS – field separator (default space) NR – current record number (starting at 1) NF – number of fields in the current record $0 – the entire current line $1…$n – the n‑th field of the current line.

Example to print the first and last fields of lines 3‑5: cat hello.txt | awk 'NR==3, NR==5{print $1,$NF}'

4. Built‑in Functions gsub(r,s) – replace occurrences of r with s in $0 index(s,t) – return position of t in s length(s) – length of string s match(s,r) – test if s matches regex r split(s,a,fs) – split s into array a using separator fs substr(s,p) – substring of s starting at position p

5. Operators Arithmetic operators similar to C (+, -, *, /, %, ++, --, +=, -=, etc.) and comparison operators (==, !=, >, >=, =~ for regex matching).

6. Control Flow BEGIN and END are special patterns that run before processing starts and after it finishes, respectively. Example to count total characters: awk ' BEGIN {count=0;} {count+=length($0);} END {print count;}' Other control structures (if, while, do…while, for, break, continue) behave like in C.

7. Interaction with the Shell - Using shell variables inside AWK: simply reference them within single quotes. #!/bin/bash STR="hello" echo | awk '{ print "${STR}"; }' - Executing shell commands from AWK: use double quotes or the system() function. #!/bin/bash echo hello | awk '{ system("date > date.txt"); }' - Passing data back to the shell is typically done via temporary files. - The getline statement reads input from a file or command into AWK variables. #!/bin/bash echo | awk '{ while (getline < "date.txt") { print $0; } }'

Conclusion: Although the title promises a one‑minute read, a careful study of this guide will give you a solid foundation in using AWK for everyday text‑processing tasks.