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perl + print to file_out in place to standard output

I have the follwoing script

#!/usr/bin/perl 
open IN, "/tmp/file"; 
s/(.*)=/$k{$1}++;"$1开发者_Python百科$k{$1}="/e and print while <IN>; 

how to print the output of the script to file_out in place to print to standard output?

lidia


#!/usr/bin/perl 
open IN, "/tmp/file"; 
open OUT, ">file_out.txt";
s/(.*)=/$k{$1}++;"$1$k{$1}="/e and print OUT while <IN>; 

Explanation:

  • `open IN, "/tmp/file"
    • open command to open file
    • IN filehandle name
    • /tmp/file name of file and specifier that it is for reading
      • if there is no modifier, it means reading
      • if there is a <, i.e. "</tmp/file" it also means reading
  • `open OUT, ">file_out.txt"
    • open command to open file
    • OUT filehandle name
    • >file_out.txt name of file and specifier that it is for reading
      • there must be a >, i.e. ">file_out.txt" to write
  • s/.../.../e your substitution (I assume you know what it does)
  • and is a boolean operator that short-circuits, meaning it only does the thing afterwards if the thing beforehand is true. In this case, it will only print if the substitution actually matched something.
  • print OUT print to the filehandle OUT
  • while <IN> for each line from the file behind filehandle IN

Note:

Used this way, it makes extensive use of the magical default variable $_. Do a search for $_ on the perlintro site. In short:

  • If you don't tell a s/// substitution what string to work on, it uses $_
  • If you don't tell a print what to print, it prints $_
  • If you don't tell a while loop going through a filehandle's data where to put each line, it gets put into $_

Your program could have been rewritten:

#!/usr/bin/perl 
open IN, "/tmp/file"; 
open OUT, ">file_out.txt";
while( defined( $line = <IN> ) )
{
  $line =~ s/(.*)=/$k{$1}++;"$1$k{$1}="/e or next;
  print OUT $line;
}


Simply add the filehandle you are printing to after the print statement; opening for writing is a small change from opening for reading:

#!/usr/bin/perl -w
open IN, "/tmp/file";
open OUT, '>', "/tmp/file_out";
s/(.*)=/Sk_$1_++;"$1Sk_$1_="/ and print OUT while <IN>;

(I munged the replacement a bit, so it was easier for me to test.)

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