remembered expression in substitution

[jjohnn]

# adds line #'s before every line that
# match the expression at the command line,
# putting parens around the matches
#

http://www.comp.leeds.ac.uk/Perl/sandtr.html

$file = 'stam.txt';
open (TEXT, $file);
my $linenum = "000";

while ($line = <TEXT>){
if($line =~/($ARGV[0])/g){
$line =~ s/$1/($ARGV[0])/g;
$linenum++;
print &quot;$linenum &quot;.&quot;$line&quot;;
}
else{
print &quot; $line&quot;;
}
}


In the substitution, I get an error (&quot;use of uninitialized value&quotwhen I try to use $1 in place of $ARGV[0]. I have tried using braces around the &quot;1&quot;, or using &quot;\1&quot; (without the quotes), but I get the same message.

 

[icrf]

try assigning $1 to a temp scalar and then using it?

if($line =~/($ARGV[0])/g){
  my $tmp = $1;
  $line =~ s/$tmp/($ARGV[0])/g;
...

----------------------------------------------------------------------------------
...but I'm just a C man trying to see the light

 

[jjohnn]

Thanks. That works as well as simply puting $ARGV[1] in the substitution, but I don't understand why the $1 doesn't work.

Incidentally, it is only the second part of the substitution expression (between the second and third slashes of s///) that complains about $1. $1 can go in the first (search) part of the substituttion expression with no complaints.

puzzling to me.

 

[jjohnn]

Almost there: there are syntax errors near the &quot;print&quot; and &quot;else&quot; lines; can somebody help me see them?

$file = 'stam.txt';
open (TEXT, $file);
my $linenum = &quot;000&quot;;

while($line=<TEXT>){
$finds =~ s/($ARGV[0])/($1)/g
if ($finds){
$linenum += $finds;
print &quot;$linenum &quot;.&quot;$line&quot;;
}
else{
print &quot; $line&quot;;
}
}

 

[rosenk]

The reason [tt]$1[/tt] doesn't work in the second part of the expression is because it is no longer the [tt]$1[/tt] from the initial matching regular expression, but the [tt]$1[/tt] from the match using the left side of the regex. You don't use any grouping, so $1 is undefined.

 

[rosenk]

The syntax error is because of a missing semicolon on the line:
[tt]$finds =~ s/($ARGV[0])/($1)/g[/tt]

 

[jjohnn]

It's embarrassing. Thanks