Perl regex $

ShaqDiesel · 08-16-2006, 04:19 PM

I want to match a line, $_ if it ends with \. There are several lines like this one after the other. Neither of these work, why?
/\\$/ nor /\\\n$/

BTW does subsititution just use the last filestream opened? Thanks.

druuna · 08-16-2006, 05:01 PM

Hi,

How are you trying to do this?

This seems to work, using /\\$/:

Code:

#!/usr/bin/perl

open(INFILE, "infile");
while (<INFILE>) {
  if (/\\$/) {
    print $_;
  }
}
close INFILE;

Hope this helps.

spirit receiver · 08-16-2006, 05:22 PM

Actually both variants should work fine.

Code:

ada@barnabas:~/tmp> cat kram
this one \
this one not
this one again\
but not this line.
ada@barnabas:~/tmp> perl -ne 'if( /\\$/){ print }' kram
this one \
this one again\
ada@barnabas:~/tmp> perl -ne 'if( /\\\n$/){ print }' kram
this one \
this one again\

ShaqDiesel · 08-18-2006, 01:21 PM

Here's some code:
#!/usr/bin/perl

$filename = $ARGV[0];
open(INFILE, $filename);
while (<INFILE>) {
if (/\\$/) {
print $_;
print "That was a match\n";
}
}
close INFILE;

Here's the input file:
This line ends with a \
This is a new line
The text file was created by typing the first line, pressing enter, typing the second line, and closing the file without pressing enter again. This program prints:
This line ends with a \
That was a match
Since "That was a match" came on a new line, the last character of the first line is obviously a newline. But this regex should have only matched lines ending with '\' because of the $, so nothing should have matched. As a matter of fact, if I make the regular expression \\\n$ I get the same result. What is going on here? Thank you.

soggycornflake · 08-18-2006, 01:45 PM

Quote:

But this regex should have only matched lines ending with '\' because of the $

$ matches BEFORE the \n, so it is working correctly.

ShaqDiesel · 08-18-2006, 02:11 PM

May I ask why it printed the same thing for \\\n$? If it doesn't look at the newline created when I pressed enter after the first line wouldn't it still not match because there is not a newline after the \?

soggycornflake · 08-18-2006, 02:40 PM

I didn't quite follow that.

$ matches at the end of the line (which by default means before the \n). If you explicitly put a \n in, then perl will match that too, as far as I can tell. Generally, you don't need to match \n explicitly.

/\\$/ matches a backslash at the end of the line (before the \n)

/\\\n$/ matches a backslash followed by a newline (which hits the absolute end of the line so is OK).

I'm not sure if all regex engines work like this, but perl does, apparently.