Selectively replacing characters inside a string

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

Hi, Monks!

I have a problem that I've come up with a reasonably nice solution for, but have been going over it in my head and wondering if it's the best solution.

I have a log file in which I want to hide file and path names. I want to preserve the appearance of a directory structure, so I do not want to hide the "/" characters that are used as directory separators.

The filename will always appear at most once per line, and will always appear inside of an easily identifiable section, like this: file="path/goes/here".

I would like to process that example so that the output looks like this: file="xxxx/xxxx/xxxx".

The solution that I came up with does exactly what I want. From the command line, I pipe it to this (this is on a Unix host):

... | perl -pe '1 while s|(file="[x/]*)[^x/"]|$1x|;'
[download]

I've been wondering if there is something simpler, like somehow being able to do s|[^/]|x|g on the text between file=" and ", but I haven't been able to figure out how.

Does anyone have any suggestions?

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Re: Selectively replacing characters inside a string by liverpole (Monsignor) on Jun 11, 2009 at 01:28 UTC
Hi markkawika, The first thing that comes to mind if you want to do it with regexes is to first capture the quoted part, and then change it: `use strict; use warnings; my $line = qq[file="path/goes/here"]; print "Line is '$line'\n"; if ($line =~ /^([^"])"([^"])"(.*)$/) { my ($prefix, $quoted, $suffix) = ($1, $2, $3); $quoted =~ s\|[^/]\|x\|g; $line = qq[$prefix"$quoted"$suffix]; } print "Line is '$line'\n";` [download] Another way, if you're sure that the expression ends with the quoted expression, would be something very simple like: `use strict; use warnings; my $line = qq[file="path/goes/here"]; print "Line is '$line'\n"; my @sections = split('"', $line); $sections[1] =~ s\|[^/]\|x\|g; $line = join('"', @sections) . '"'; print "Line is '$line'\n";` [download] Both result in: `Line is 'file="path/goes/here"' Line is 'file="xxxx/xxxx/xxxx"'` [download] Both are less simple than your solution, of course, but keep things within Perl, without resorting to using the shell. s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/	[reply] [d/l] [select]
Re: Selectively replacing characters inside a string by johngg (Canon) on Jun 11, 2009 at 10:46 UTC
Similar to AnomalousMonk's solution but using look-behind and -ahead assertions and tr with the "complement" flag. `use strict; use warnings; open my $logFH, q{<}, \ <<EOD or die qq{open: << HEREDOC: $!\n}; 2009/06/09 10:11:12 read error: file="/path/to/file" reason: gone 2009/06/09 12:43:27 created: file="/path/to/file" EOD while( <$logFH> ) { s{(?<= file=" ) ( [^"]+ ) (?= " )} {do { my $cap = $1; $cap =~ tr{/}{x}c; $cap }}xeg; print; }` [download] The output. `2009/06/09 10:11:12 read error: file="/xxxx/xx/xxxx" reason: gone 2009/06/09 12:43:27 created: file="/xxxx/xx/xxxx"` [download] I hope this is of interest. Cheers, JohnGG	[reply] [d/l] [select]
Re^2: Selectively replacing characters inside a string by markkawika (Monk) on Jun 11, 2009 at 16:54 UTC
Thank you, JohnGG, that was exactly what I was trying to accomplish yesterday on my own, but you've done it much more succinctly than I did.	[reply]
Re: Selectively replacing characters inside a string by AnomalousMonk (Archbishop) on Jun 11, 2009 at 05:15 UTC
It's also possible to use nested substitutions (I've use single-quotes instead of double-quotes to avoid the WinNoyance® of escaping a bunch of "s): `>perl -wMstrict -le "for my $str (@ARGV) { print $str; $str =~ s{ (' [^']* ') } { (my $x = $1) =~ s{ [^'/] }{x}xmsg; $x }xmsge; print $str; } " file='path/goes/here' foo'a/b/c'bar '///' 'a/b/c' file1='aa/bb/cc',file2='/dd/' file='path/goes/here' file='xxxx/xxxx/xxxx' foo'a/b/c'bar foo'x/x/x'bar '///' '///' 'a/b/c' 'x/x/x' file1='aa/bb/cc',file2='/dd/' file1='xx/xx/xx',file2='/xx/'` [download]	[reply] [d/l]
Re: Selectively replacing characters inside a string by dsheroh (Monsignor) on Jun 11, 2009 at 09:57 UTC
If I'm reading correctly that you want to replace all non-slash characters with the letter x, the easiest way would seem to be to use `tr` rather than a regex: `$ perl -e '$foo = "/some/path/to/a/file"; $foo =~ tr\|/\|x\|c; print "$fo +o\n";' /xxxx/xxxx/xx/x/xxxx` [download]	[reply] [d/l] [select]
Re^2: Selectively replacing characters inside a string by markkawika (Monk) on Jun 11, 2009 at 16:42 UTC
I do want to replace all non-slash characters with the letter x, but only on a portion of the input string. Specifically, the part between the quotes in `file="some/path"`. And actually, I didn't make it clear, but there will be text before and after the `file="some/path"`, so I have to be careful about what I substitute. The actual input line would look more like: `2009-06-10 19:37:29 GMT [more text here] file="some/path" status=0 des +tination="some more text"` [download] And the only thing I want to filter is the path inside of the `file="some/path"` stuff.	[reply] [d/l] [select]