How can I output null-terminated strings in Awk?

Question

I\'m working on a shell script that will be used by others, and may ingest suspect strings. It\'s based around awk, so as a basic resiliency measure, I want to have awk outp

Answer 1

There are three alternatives:

1. Setting ORS to ASCII zero: Other solutions have awk -vORS=$'\0' but:
   The $'\0' is a construct specific to some shells (bash,zsh).
   So: this command awk -vORS=$'\0' will not work in most older shells.

There is the option to write it as: awk 'BEGIN { ORS = "\0" } ; { print $0 }', but that will not work with most awk versions.

2. Printing (printf) with character \0: awk '{printf( "%s\0", $0)}'

3. Printing directly ASCII 0: awk '{ printf( "%s%c", $0, 0 )}'

Testing all alternatives with this code:

#!/bin/bash

test1(){   # '{printf( "%s%c",$0,0)}'|
    a='awk,mawk,original-awk,busybox awk'
    IFS=',' read -ra line <<<"$a"
    for i in "${line[@]}"; do
        printf "%14.12s %40s" "$i" "$1"
        echo -ne "a\nb\nc\n" |
        $i "$1"|
        od -cAn;
    done
}

#test1 '{print}'
test1 'BEGIN { ORS = "\0" } ; { print $0 }'
test1 '{ printf "%s\0", $0}'
test1 '{ printf( "%s%c", $0, 0 )}'

We get this results:

            awk      BEGIN { ORS = "\0" } ; { print $0 }   a  \0   b  \0   c  \0
           mawk      BEGIN { ORS = "\0" } ; { print $0 }   a   b   c
   original-awk      BEGIN { ORS = "\0" } ; { print $0 }   a   b   c
    busybox awk      BEGIN { ORS = "\0" } ; { print $0 }   a   b   c
            awk                     { printf "%s\0", $0}   a  \0   b  \0   c  \0
           mawk                     { printf "%s\0", $0}   a   b   c
   original-awk                     { printf "%s\0", $0}   a   b   c
    busybox awk                     { printf "%s\0", $0}   a   b   c
            awk               { printf( "%s%c", $0, 0 )}   a  \0   b  \0   c  \0
           mawk               { printf( "%s%c", $0, 0 )}   a  \0   b  \0   c  \0
   original-awk               { printf( "%s%c", $0, 0 )}   a  \0   b  \0   c  \0
    busybox awk               { printf( "%s%c", $0, 0 )}   a   b   c

As it can be seen above, the first two solutions work only in GNU AWK.

The most portable is the third solution: '{ printf( "%s%c", $0, 0 )}'.

No solution work correctly in "busybox awk".

The versions used for this tests were:

          awk> GNU Awk 4.0.1
         mawk> mawk 1.3.3 Nov 1996, Copyright (C) Michael D. Brennan
 original-awk> awk version 20110810
      busybox> BusyBox v1.20.2 (Debian 1:1.20.0-7) multi-call binary.

Answer 2

You can also pipe your awk's output through tr:

awk '{...code...}' infile | tr '\n' '\0' > outfile

Just tested, it works at least on Linux and FreeBSD.

If you cannot use newlines as separators (for example, if output records can contain newlines inside), just use some other character that's guaranteed not to appear inside a record, e.g. the one with code 1:

awk 'BEGIN { ORS="\001" } {...code...}' | tr '\001' '\0'

Answer 3

I've solved printing ASCII 0 from awk. I use UNIX command printf "\000"

echo | awk -v s='printf "\000"' '{system(s);}'

Answer 4

Alright, I've got it.

awk '{printf "%s\0", $0}'

Or, using ORS,

awk -vORS=$'\0' //