Question

I have the following line in a Perl script:

my $temp = `sed 's/ /\n/g' /sys/bus/w1/devices/w1_bus_master1/10-000802415bef/w1_slave | grep t= | sed 's/t=//'`;

Which throws up the error:
“sed: -e expression #1, char 2: unterminated `s’ command”

If I run a shell script as below it works fine:

temp1=`sed 's/ /\n/g' /sys/bus/w1/devices/w1_bus_master1/10-000802415bef/w1_slave | grep t= | sed 's/t=//'`
echo $temp1

Anyone got any ideas?

Answer 1

Perl interpretes your \n as a literal newline character. Your command line will therefore look something like this from sed’s perspective:

sed s/ /
/g ...

which sed doesn’t like. The shell does not interpret it that way.

The proper solution is not to use sed/grep in such a situation at all. Perl is, after all, very, very good at handling text. For example (untested):

use File::Slurp;
my @lines = split m/\n/, map { s/ /\n/g; $_ } scalar(read_file("/sys/bus...));
@lines    = map { s/t=//; $_ } grep { m/t=/ } @lines;

Alternatively escape the \n once, e.g. sed 's/ /\\n/g'....