three levels of parenthesis/quoting in shell snippets in tcsh?

Question

I'm using tcsh; I want to run some snippet from sh on the command line, which itself contains a perl snippet, which contains some strings that are to be printed.

This results in three levels of parentheses, but there are only two available — " and '.

Is there a way around?

tcsh# sh -c 'while (true); do mtr --order "SRL BGAWV M" …; hping --icmp-ts --count 12 … | perl -ne '... if (/tsrtt=(\d+)/) {print $0,"\t"…}' ; done'

Answer 1

To include a single quote inside of single quotes, use '\''. e.g.

perl -ne'... print $0, "\t" ...'

becomes

sh -c '... | perl -ne'\''... print $0, "\t" ...'\'''

---

In this particular case, an alternative is to replace

perl -ne'... print $0, "\t" ...'

with

perl -ne"... print \$0, qq{\t} ..."

so you'd get

sh -c '... | perl -ne"... print \$0, qq{\t} ..."'

---

I'd just write the whole thing in Perl

perl -e'
    while (1) {
       system("mtr", "--order", "SRL BGAWV M");

       open(my $pipe, "-|", "hping", "--icmp-ts", "--count", "12");
       while (<$pipe>) {
          ...
       }
    }
'

Answer 2

Use q/../ for single quotes and qq/.../ for double quotes within your Perl code.

For instance, print $0, qq/\t/

Answer 3

Another solution is doing a big and long echo, with a few arguments, all escaped with ', where the actual literal ' is gathered from the result of executing printf "'", and piping this whole echo to sh, instead of passing the string as an argument directly to sh.

This actually seems somewhat easier, because it doesn't involve escaping the whole perl snippet, basically, but only escaping the two ' that are used for perl -ne.

tcsh# echo 'while (true); do mtr --order "SRL BGAWV M" …; hping --icmp-ts --count 12 … | perl -ne' `printf "'"` '... if (/tsrtt=(\d+)/) {print $0,"\t"…}' `printf "'"` '; done' | sh