How do I replace regex with $var in this command?
echo "$many_lines" | sed -n '/regex/{g;1!p;};h'
$var could look like fs2@auto-17.
The sed command will output the line immediately before a regex, but not the line containing the regex.
If all this can be done easier with a Perl one-liner, then it is fine with me.
It is not beautiful, but this gives me the previous line to $var which is want I wanted.
echo "$many_lines" | grep -B1 "$var" | grep -v "$var"
In Perl regexes, you can interpolate variable contents into regexes like /$foo/. However, the contents will be interpreted as a pattern. If you want to match the literal content of $foo, you have to escape the metacharacters: $safe = quotemeta $foo; /$safe/. This can be shortended to /\Q$foo\E/, which is what you usually want. A trailing \E is optional.
I don't know if the sed regex engine has a similar feature.
A Perl one-liner: perl -ne'$var = "..."; print $p if /\Q$var/; $p=$_'
%ENV variable. $ENV{PATH}Use double quotes instead of single quotes to allow variable expansion:
echo $many_lines | sed -n "/$var/"'{g;1!p;};h'
"/$var/{g;1ps -p 1779;};h" and the error invalid command code f
$var does not contain any unescaped forward slashes.Since you are looking for a line before the regex, with a single one liner it will not be that trivial and beautiful, but here is how I will do it (Using Perl only):
echo "$many_lines" | perl -nle 'print $. if /\Q$var/' | while read line_no; do
export line_no
echo $many_lines | perl -nle 'print if $. - 1 == $ENV{line_no}'
done
or if you want to do in one line
echo "$many_lines" | perl -nle 'BEGIN {my $content = ""; } $content .= $_; END { while ($content =~ m#([^\n]+)\n[^\n]+\Q$var#gosm) { print $1 }}'
Or this one, should definitely match:
echo "$many_lines" | perl -nle 'BEGIN {my @contents; } push @contents, $_; if ($contents[-1] =~ m#\Q$var#o)') { print $contents[-2] if defined $contents[-2]; }
Or you can use here-documents too, if you don't want to escape the double quotes!
In Perl it looks like this:
$heredoc = <<HEREDOC;
here is your text and $var is your parameter
HEREDOC
Its important to end the heredoc with the same string you began, in my example its "HEREDOC" in a new line!
echo $many_lineswon't work the way you expect unless you quote:echo "$many_lines"sedcode, I think you're out of luck.