grep non printable characters

Shell Programming and Scripting
1

Sometimes obvious things... are not so obvious. I always thought that it was possible to grep non printable characters but not with my GNU grep (5.2.1) version.

printf "Hello\tWorld" | grep -l '\t'
printf "Hello\tWorld" | grep -l '\x09'
printf "Hello\tWorld" | grep -l '\x{09}'

None of them work. I know that work-arounds with od, cat -vet or sed are possible but why not simply with grep that is meant to do this type of job?

What am I doing wrong?

2

Try like this:

$ printf 'hello\tworld' | grep $'\t'
3

With grep you can match control characters like this:

grep '[[:cntrl:]]'

And non printable characters like this:

grep '[^[:print:]]'

Another workaround with shells expanding the special construct $'\X' (ksh93, bash, zsh):

zsh-4.3.4% printf "Hello\tWorld"|grep -l $'\t'
(standard input)
zsh-4.3.4% printf "Hello\tWorld"|grep -l $'\x09'
(standard input)
4

Thanks to both it works fine with the $'\x' construct in ksh and bash. Nice to know.