Could sed or awk use NUL character as record separator?

Question

I have a NUL delimited output coming from the following command :

some commands | grep -i -c -w -Z 'some regex'

The output consists of records of the format :

[file name]\0[pattern count]\0

I want to use text manipulation tools, such as sed/awk, to change the records to the following format :

[file name]:[pattern count]\0

But it seems that sed/awk usually handles only records delimited by the "newline" character. I would like to know that how sed/awk could be used to achieve my purpose, or if sed/awk could not handle such case what other Linux tool should I use.

Thanks for any suggestion.

Lawrence

Answer 1

By default, the record separator is the newline character, defining a record to be a single line of text. You can use a different character by changing the built-in variable RS. The value of RS is a string that says how to separate records; the default value is "\n", the string containing just a newline character.

 awk 'BEGIN { RS = "/" } ; { print $0 }' BBS-list

Answer 2

Since version 4.2.2, GNU sed has the -z or --null-data option to do exactly this. Eg:

sed -z 's/old/new' null_separated_infile

Answer 3

Yes, gawk can do this, set the record separator to \0. For example the command

gawk 'BEGIN { RS="\0"; FS="=" } $1=="LD_PRELOAD" { print $2 }' </proc/$(pidof mysqld)/environ

Will print out the value of the LD_PRELOAD variable:

/usr/lib/x86_64-linux-gnu/libjemalloc.so.1

The /proc/$PID/environ file is a NUL separated list of environment variables. I'm using it as an example, as it's easy to try on a linux system.

The BEGIN part sets the record separator to \0 and the field separator to = because I also want to extract the part after = based on the part before =.

The $1=="LD_PRELOAD" runs the block if the first field has the key I'm interested in.

The print $2 block prints out the string after =.

---

But mawk cannot parse input files separated with NUL. This is documented in man mawk:

BUGS
       mawk cannot handle ascii NUL \0 in the source or data files.

mawk will stop reading the input after the first \0 character.

---

You can also use xargs to handle NUL separated input, a bit non-intuitively, like this:

xargs -0 -n1 </proc/$$/environ

xargs is using echo as the default comand. -0 sets the input to be NUL separated. -n1 sets the max arguments to echo to be 1, this way the output will be separated by newlines.

---

And as Graeme's answer shows, sed can do this too.

Answer 4

Using sed for removing the null characters -

sed 's/\x0/ /g' infile > outfile

or make in-file substitution by doing (this will make backup of your original file and overwrite your original file with substitutions).

sed -i.bak 's/\x0/ /g' infile

Using tr:

tr -d "\000" < infile > outfile