Question

我用了一种能够扩大“不ix”环境变量的手稿。该书记上课。文字如下:

# I know this should not be typed here. This is here just for testing.
@ENV{qw(LKUP_DIR DATA_DIR CTRL_DIR MMM)} = qw(/appl1/TSS/lkup /appl1/TSS/data /appl1/TSS/ctrl Oct);
while ( <DATA> )
{
  my $line=$_;
  chomp $line;
  $line =~ s{$(w+)}{ exists $ENV{$1} ? $ENV{$1} :  $ .$1 }ge;
  $line =~ s{${(w+)}}{ exists $ENV{$1} ? $ENV{$1} :  ${ .$1. }  }ge;
  print "$line
";
}

__DATA__
${LKUP_DIR}/lookup_file.txt
${CTRL_DIR}/ctrl_file_$MMMM.txt
$CTRL_DIR/ctrl_file_$MMM.txt

我想将这一文字改为一行,但我不相信如何处理上文提及的文字中使用的固定表述中的单项报价。我尝试如下,但当然不是:

perl -lne  $line=$_; $line =~ s{$(w+)}{ exists $ENV{$1} ? $ENV{$1} :  $ .$1 }ge; $line =~ s{${(w+)}}{ exists $ENV{$1} ? $ENV{$1} :  ${ .$1. }  }ge; print "$line";  DATA.txt

Any suggestions? (I want to do this only in Perl.)

Answer 1

I agree with @Mat: it seems a bad idea. It will be just one line but you lose on readability. Just think that you might edit a year later and still try to understand what the one liner does.

但无论如何,在Perl,你可以使用<条码>q/STRING/code>而不是<条码>。

perl -lne  $line=$_; $line =~ s{$(w+)}{ exists $ENV{$1} ? $ENV{$1} : q/$/.$1 }ge; $line =~ s{${(w+)}}{ exists $ENV{$1} ? $ENV{$1} : q/${/.$1.q/}/ }ge; print "$line";  DATA.txt

Answer 2

Here s a more concise version of your script. A notable difference is that I use // instead of exists. I think that the difference, where environment variables are concerned, would be negligible. If an environment variable exists, but is undefined, what is it? If it truly would be undefined, it would cause a warning when perl prints it.

perl -wpe  s#${?(w+)}?# $ENV{$1} // $& #ge;  DATA.txt

If you still insist on using exist, simply use:

perl -wpe  s#${?(w+)}?# exists $ENV{$1} ? $ENV{$1} : $& #ge;  DATA.txt

What I did:

Removed the useless transition variable $line
Removed -l option
Exchanged -n and print with -p
Change delimiter on the substitution to not have to escape {}
Combined the regexes by adding }? as an optional match
Used $& -- entire match -- instead of trying to puzzle the parts of the match back together

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