Multiple substr in Perl one-liner

dirtdog has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks, I'm trying to replace multiple fields with blank spaces using one-liner

It works when i do one at a time, but not when i try and combine them

perl -ne 'substr ( $_,2,8 ) = "        " && substr ( $_,15,5 ) = "    
+ " if /^AB/ ; print $_;' $1 > $1.tmp
[download]

The simple test file is AB2014052012345HELLOWORLD

 For some reason I end up with the following result:
AB     12345     WORLD
[download]

there should be 8 blank spaces after AB, but i'm only getting 5. I am, however, correctly getting 5 spaces before WORLD.

Any help is much appreciated

Comment on Multiple substr in Perl one-liner Select or Download Code

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Re: Multiple substr in Perl one-liner by Anonymous Monk on May 19, 2014 at 16:25 UTC
It's a precedence issue, the `&&` is binding stronger than you think. Use extra parens, or use `and`, which has lower precedence. See perlop for the precedence table. Here's an explanation-by-code: $ perl -MO=Deparse,-p -e 'substr ( $_,2,8 ) = " " && substr ( $ +_,15,5 ) = " " if /^AB/' (/^AB/ and substr($_, 2, 8) = (substr($_, 15, 5) = ' ')); $ perl -MO=Deparse,-p -e 'substr ( $_,2,8 ) = " " and substr ( +$_,15,5 ) = " " if /^AB/' (/^AB/ and ((substr($_, 2, 8) = ' ') and substr($_, 15, 5) = ' + ')); $ echo "AB2014052012345HELLOWORLD" \| perl -pe 'substr ( $_,2,8 ) = " + " && substr ( $_,15,5 ) = " " if /^AB/' AB 12345 WORLD $ echo "AB2014052012345HELLOWORLD" \| perl -pe 'substr ( $_,2,8 ) = " + " and substr ( $_,15,5 ) = " " if /^AB/' AB 12345 WORLD [download]	[reply] [d/l] [select]
Re^2: Multiple substr in Perl one-liner by dirtdog (Monk) on May 19, 2014 at 16:34 UTC
ahhh...makes sense now. Thank you!	[reply]