AWK Cheatsheet

001.awk_cheatsheet.txt

# How to just buffer each line (rather than the entire input stream) when using awk / gawk to read data from a pipe.
  awk '{ print $0 ; system("") }' # compatible with POSIX complient systems
  gawk '{ print $0 ; system("") }' # gawk is smart and will not actually start a sub-shell

  # fflush - is going to offer something similar (although you can speicify which kind of output you would like to flush).
 
  # remove first column (using white space) keep all other columns
  awk '{sub(/^[^[:space:]]+[[:space:]]+/, ""); print}'

500.insert_after_first.awk

# This script inserts contents of replace.txt after the first occurrence of "<REPLACE_/AFTER/_ME>"
/<REPLACE_\/AFTER\/_ME>/ && !found {
  found = 1
  print $0
  # Insert contents of replace.txt after the first match
  while ((getline line < "replace.txt") > 0) {
    print line
  }
}
# Print the current line if it does not match the target string
!/<REPLACE_\/AFTER\/_ME>/ { print $0 }

501.add_the_text.bash

#!/usr/bin/env bash

# this script uses the awk script 500.insert_after_first.awk
# to add the data from replace.txt into the files feed into the
# while loop.

while IFS= read -r current_file ; do
	echo " processing : $current_file"
	temp_file=$(mktemp ./mytmp.XXXXXXXX)
	awk -f add.awk $current_file > $temp_file
	if [[ $? != 0 ]] ; then
		echo "ERROR! AWK failed aborting.."
		exit -99
	fi
	mv "$temp_file" $current_file
	if [[ $? != 0 ]] ; then 
                echo "ERROR! moving failed aborting.."
                exit -99
        fi
done <<< $(ls /path/to/input_data_to_update/*/*/*.txt)

600.insert_every_x_lines.txt

# insert every 5 lines hostname weather a service (systemd) nginx is active.
tail -f /path/to/my/file.log | awk 'NR % 5 == 0 {system(" echo -n $(hostname) ; echo -n  \" : nginx status : \" ; systemctl is-enabled nginx.service") } {print}'