Perl - Why I can't use a variable into regex?












1















Why can't I use if($l =~ $ARGV[0]) but I can use if($l =~ /$ARGV[0]/g?



first case

$ perl script.pl '/^[w]/g'


second case

$ perl script.pl '^[w]'





perl







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    1















    Why can't I use if($l =~ $ARGV[0]) but I can use if($l =~ /$ARGV[0]/g?



    first case

    $ perl script.pl '/^[w]/g'


    second case

    $ perl script.pl '^[w]'





    perl







    share|improve this question



























      1












      1








      1








      Why can't I use if($l =~ $ARGV[0]) but I can use if($l =~ /$ARGV[0]/g?



      first case

      $ perl script.pl '/^[w]/g'


      second case

      $ perl script.pl '^[w]'





      perl







      share|improve this question
















      Why can't I use if($l =~ $ARGV[0]) but I can use if($l =~ /$ARGV[0]/g?



      first case

      $ perl script.pl '/^[w]/g'


      second case

      $ perl script.pl '^[w]'





      perl




      perl






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited 24 mins ago









      Rui F Ribeiro

      40.1k1479136




      40.1k1479136










      asked Dec 13 '15 at 16:50









      The dudeThe dude

      1259




      1259






















          1 Answer
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          $ARGV[0] is a scalar string. When you do if($l =~ $ARGV[0]) and $ARGV[0] is '/^[w]/g' this is equivalent to if($l =~ '/^[w]/g') instead of if($l =~ /^[w]/g). In the former case the slashes are simply characters in a string while in the later they are a part of the Perl syntax that delimits a regular expression.






          share|improve this answer





















          • 2





            To work around this, you can use $regex = qr{$ARGV [0]}

            – Joseph R.
            Dec 13 '15 at 20:03













          • Hey, thanks for the advice guys. Could you take a look at this question mentioning other error in the same script? unix.stackexchange.com/questions/249368/…

            – The dude
            Dec 14 '15 at 21:08













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          1 Answer
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          1 Answer
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          active

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          active

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          active

          oldest

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          3














          $ARGV[0] is a scalar string. When you do if($l =~ $ARGV[0]) and $ARGV[0] is '/^[w]/g' this is equivalent to if($l =~ '/^[w]/g') instead of if($l =~ /^[w]/g). In the former case the slashes are simply characters in a string while in the later they are a part of the Perl syntax that delimits a regular expression.






          share|improve this answer





















          • 2





            To work around this, you can use $regex = qr{$ARGV [0]}

            – Joseph R.
            Dec 13 '15 at 20:03













          • Hey, thanks for the advice guys. Could you take a look at this question mentioning other error in the same script? unix.stackexchange.com/questions/249368/…

            – The dude
            Dec 14 '15 at 21:08


















          3














          $ARGV[0] is a scalar string. When you do if($l =~ $ARGV[0]) and $ARGV[0] is '/^[w]/g' this is equivalent to if($l =~ '/^[w]/g') instead of if($l =~ /^[w]/g). In the former case the slashes are simply characters in a string while in the later they are a part of the Perl syntax that delimits a regular expression.






          share|improve this answer





















          • 2





            To work around this, you can use $regex = qr{$ARGV [0]}

            – Joseph R.
            Dec 13 '15 at 20:03













          • Hey, thanks for the advice guys. Could you take a look at this question mentioning other error in the same script? unix.stackexchange.com/questions/249368/…

            – The dude
            Dec 14 '15 at 21:08
















          3












          3








          3







          $ARGV[0] is a scalar string. When you do if($l =~ $ARGV[0]) and $ARGV[0] is '/^[w]/g' this is equivalent to if($l =~ '/^[w]/g') instead of if($l =~ /^[w]/g). In the former case the slashes are simply characters in a string while in the later they are a part of the Perl syntax that delimits a regular expression.






          share|improve this answer















          $ARGV[0] is a scalar string. When you do if($l =~ $ARGV[0]) and $ARGV[0] is '/^[w]/g' this is equivalent to if($l =~ '/^[w]/g') instead of if($l =~ /^[w]/g). In the former case the slashes are simply characters in a string while in the later they are a part of the Perl syntax that delimits a regular expression.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited Dec 13 '15 at 17:34

























          answered Dec 13 '15 at 17:26









          nwknwk

          663513




          663513








          • 2





            To work around this, you can use $regex = qr{$ARGV [0]}

            – Joseph R.
            Dec 13 '15 at 20:03













          • Hey, thanks for the advice guys. Could you take a look at this question mentioning other error in the same script? unix.stackexchange.com/questions/249368/…

            – The dude
            Dec 14 '15 at 21:08
















          • 2





            To work around this, you can use $regex = qr{$ARGV [0]}

            – Joseph R.
            Dec 13 '15 at 20:03













          • Hey, thanks for the advice guys. Could you take a look at this question mentioning other error in the same script? unix.stackexchange.com/questions/249368/…

            – The dude
            Dec 14 '15 at 21:08










          2




          2





          To work around this, you can use $regex = qr{$ARGV [0]}

          – Joseph R.
          Dec 13 '15 at 20:03







          To work around this, you can use $regex = qr{$ARGV [0]}

          – Joseph R.
          Dec 13 '15 at 20:03















          Hey, thanks for the advice guys. Could you take a look at this question mentioning other error in the same script? unix.stackexchange.com/questions/249368/…

          – The dude
          Dec 14 '15 at 21:08







          Hey, thanks for the advice guys. Could you take a look at this question mentioning other error in the same script? unix.stackexchange.com/questions/249368/…

          – The dude
          Dec 14 '15 at 21:08




















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