AWK fundamental to advanced

1.awk-variables.md

Variables	Description
ENVIRON	An associative array of environment variables.
FIELDWIDTHS	Specify the field width
FS	The field seperator
RS	The record seperator, default is new line
NF	The number of fields in the current record
NR	The number of the current record
FNR	Similar to NR, but relative to the current file. It is useful when AWK is operating on multiple files. Value of FNR resets with new file.
OFS	The output field seperator, space by default
ORS	The output record seperator
FILENAME	Hold the processed file name
IGNORECASE	Ignore character case
$n	The nth field in the current record where the fields are separated by FS

Source: Mastering Linux Shell Scripting & AWK-Built-in Variables

2.awk-basic-usage.md

Usage examples

---

Basic usage:

awk 'BEGIN {FS=":"} {OFS=".|--|"} {print NR, $1} END {print FILENAME, "Total: " NR}' /etc/passwd 

Condition AWK:

awk 'BEGIN {FS=":"} $3 > 100 {print FNR, $1, $3} END {print FILENAME, "Total: " FNR}' /etc/passwd

Basic format output

awk 'BEGIN {FS=":"} {printf "%20s %6d %25s\n", $1, $4, $7}' /etc/passwd

Basic format output with header (-20 mean: 20 characters left-align, 6 means: 6 characters right-align)

awk 'BEGIN {FS=":";printf "%-20s %6s %25s\n", "Name", "UID", "Shell"} $4 >= 1000 {printf "%-20s %6d %25s\n", $1, $4, $7}' /etc/passwd

Basic format output using file passwd.awk

awk -f passwd.awk /etc/passwd

3.passwd.awk

function green(s) {
        printf "\033[1;32m" s "\033[0m\n"
}
BEGIN {
        FS=":"
        green("     Name:   UID:             Shell:")
}
{
        if ($3 > 999)
        printf "%10s %6d %18s\n", $1, $3, $7
}