awk

Script

vi script.awk

BEGIN { print "Before processing file" }
{ print NR,$0 }
END { print "After processing file" }

awk -f script.awk foo.txt
# ./script.awk foo.txt

Commands

Print complete file

awk '{print}' foo.txt

Print lines having text

awk '/text/ {print}' foo.txt

Print first and third field

# Separate by comma (,)
awk '{print $1 "," $3}' foo.txt

# Separate by space
awk '{print $1,$3}' foo.txt

Print selected line

# Print third line
awk 'NR==3 {print NR,$0}' foo.txt

# Print 3rd to 6th line
awk 'NR==3, NR==6 {print NR,$0}' foo.txt

Print first and last field

awk '{print $1,$NF}' foo.txt

Find max length line

awk '{ if (length($0) > max) max = length($0) } END { print max }' foo.txt

Insert in empty file

sudo touch myfile.txt

sudo awk -i inplace 'BEGINFILE {print "foo\tbar\nline\t2"}' myfile.txt