Question

Grepping non printable characters doesn’t seem to work for carriage return (control key ^M).

usr@R923047 ~
$ head -3 test.ctl
row 1
row 2
row 3
usr@R923047 ~
$ head -3 test.ctl | cat -nv
     1  row 1^M
     2  row 2^M
     3  row 3
usr@R923047 ~
$ head -3 test.ctl | grep '[^[:print:]]'

usr@R923047 ~
$ head -3 test.ctl | grep '[[:cntrl:]]'

usr@R923047 ~

Answer 1

According to the grep man-page, you can specify -U or --binary to:

Treat the file(s) as binary. By default, under MS-DOS and MS-Windows, grep guesses the file
type by looking at the contents of the first 32KB read from the file. If grep decides the
file is a text file, it strips the CR characters from the original file contents (to make
regular expressions with ^ and $ work correctly). Specifying -U overrules this guesswork,
causing all files to be read and passed to the matching mechanism verbatim; if the file is a
text file with CR/LF pairs at the end of each line, this will cause some regular expressions
to fail. This option has no effect on platforms other than MS-DOS and MS-Windows.

So:

$ head -3 test.ctl
row 1
row 2
row 3
$ head -3 test.ctl | cat -nv
     1  row 1^M
     2  row 2^M
     3  row 3
$ head -3 test.ctl | grep '[^[:print:]]'

$ head -3 test.ctl | grep '[[:cntrl:]]'

$ head -3 test.ctl | grep -U '[^[:print:]]'
row 1
row 2

$ head -3 test.ctl | grep -U '[[:cntrl:]]'
row 1
row 2