Re: Search and replace in all odd lines

use strict;
use warnings;

while (<DATA>) {
    s/a/x/g unless $. & 1;
    print;
}

__DATA__
Anyone know a way to apply a
substitution in a file to every
other line rather
than the hole file?
[download]

Prints:

Anyone know a way to apply a
substitution in x file to every
other line rather
thxn the hole file?
[download]

DWIM is Perl's answer to Gödel

Comment on Re: Search and replace in all odd lines Select or Download Code

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Re^2: Search and replace in all odd lines by jesuashok (Curate) on Jun 25, 2007 at 10:52 UTC
`perl -i.bak -nle 's/search/replace/g unless $. & 2; print' file(s)` [download] The above will apply the changes in line numbers 1,3,5,7,...... `perl -i.bak -nle 's/search/replace/g unless $. & 1; print' file(s)` [download] The above will apply the changes in line numbers 2,4,6,8,...... NOTE: Based on the idea from Re: Search and replace in all odd lines by GrandFather	[reply] [d/l] [select]
Re^3: Search and replace in all odd lines by johngg (Canon) on Jun 25, 2007 at 13:36 UTC
`perl -i.bak -nle 's/search/replace/g unless $. & 2; print' file` Your one-liner is not going to do what you think. `$. & 2` is going to evaluate to true whenever the ~~third~~ second bit from the right (2 is binary 100) is set. Given this input file (lines.txt) `line 1 line 2 line 3 line 4 line 5 line 6 line 7 line 8 line 9` [download] adapting your one-liner to just print the lines gives `$ perl -nle 'print unless $. & 2;' lines.txt line 1 line 4 line 5 line 8 line 9` [download] Did you actually test your adaptation of GrandFather's idea before posting? Changing between odd and even is as simple as `if $. & 1` and `unless $. & 1`. Perhaps you could have a look at "Bitwise And" in perlop to further your understanding. Cheers, JohnGG Update: Corrected typo. Update 2: Corrected huge balls-up, thanks fenLisesi. Where did I get "2 is binary 100" from? Update 3: And thanks clinton, saw your reply after /msg from fenLisesi	[reply] [d/l] [select]
Re^4: Search and replace in all odd lines by clinton (Priest) on Jun 25, 2007 at 14:54 UTC
you missed another typo - 2 is binary 10, not 100 To flesh out the reasoning: `DECIMAL BINARY TRUE / FALSE ============= ================= ============ 0 & 2 == 0 000 & 010 == 000 FALSE 1 & 2 == 0 001 & 010 == 000 FALSE 2 & 2 == 2 010 & 010 == 010 TRUE 3 & 2 == 2 011 & 010 == 010 TRUE 4 & 2 == 0 100 & 010 == 000 FALSE 5 & 2 == 0 101 & 010 == 000 FALSE 6 & 2 == 2 110 & 010 == 010 TRUE 7 & 2 == 2 111 & 010 == 010 TRUE` [download] Clint	[reply] [d/l]
Re^5: Search and replace in all odd lines by johngg (Canon) on Jun 25, 2007 at 15:02 UTC