using command substitution inside a sed script, with arguments

Question

I am trying to write a short script in which I use sed to search a stream, then perform a substitution on the stream based on the results of a shell function, which requires arguments from sed, e.g.

#!/bin/sh

function test {
    echo "running test"
    echo $1
    }

sed -n -e "s/.*\(00\).*/$(test)/p" < testfile.txt

where testfile.txt contains:

1234
2345
3006
4567

(with newlines between each; they are getting removed by your sites formatting). So ok that script works for me (output "running test"), but obviously has no arguments passed to test. I would like the sed line to be something like:

sed -n -e "s/.*\(00\).*/$(test \1)/p" < testfile.txt

and output:

running test
00

So that the pattern matched by sed is fed as an argument to test. I didn't really expect the above to work, but I have tried every combination of $() brackets, backticks, and escapes I could think of, and can find no mention of this situation anywhere. Help?

Answer 1

Sed won't execute commands. Perl will, however, with the /e option on a regex command.

perl -pe 'sub testit { print STDERR "running test"; return @_[0]; }; s/.*(00).*/testit($1)/e' <testfile.txt

Redirect stderr to /dev/null if you don't want to see it in-line and screw up the output.

Answer 2

This might work for you:

tester () { echo "running test"; echo $1; }
export -f tester
echo -e "1234\n2345\n3006\n4567" |
sed -n 's/.*\(00\).*/echo "$(tester \1)"/p' | sh
running test
00

Or if your using GNU sed:

echo -e "1234\n2345\n3006\n4567" |
sed -n 's/.*\(00\).*/echo "$(tester \1)"/ep'
running test
00

N.B. You must remember to export the function first.

Answer 3

try this:

sed -n -e "s/.*\(00\).*/$1$2/p" testfile.txt | sh

Note: I might have the regex wrong, but the important bit is piping to shell (sh)