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06.29.10
Search And Replace A Block Of Text With Perl
 By
Michael Marr
Searching for and then replacing text is such a fundamental function in computing that I was eager to take the opportunity to do such an operation over a large website still being served via static HTML pages.
I quickly assumed that armed with the right regular expression, I could easily conquer this task. However, this quickly became a tale of defeat followed by outstanding victory with the help of Perl.
My first option was to find a *nix command line tool to run my search and replace operation. Apparently, >sed is this kind of tool. However, after spending hours trying to find a proper regular expression to do what I needed, I had to abandoned this option. The problem was that my search string contained multiple lines, and no matter how I tried, I couldn't get >sed to play nice with multiple lines. I was able to find a single line and replace it, but obviously this was not the complete operation I needed.
My next task was to use a PERL script and attempt to accomplish the same thing as >sed does. However, my various attempts to do the same was too on-point, as again I was only able to work with single lines. Luckily, I found this script. Following the instructions supplied by the author gave me a working script. However, as most things in life, this was not 100% tailored to my intended purpose. The script works great on one directory, but the site I was needing to run a search and replace on was spread across multiple directories and subdirectories. I needed to run this script across all the files recursively. Here's how I did it:
find ./ -name '*.html' -exec perl -pi -0777 sub.pl {} \;
Executing the command >find across the current directory will also search all subdirectories for any file with .html in the name. Obviously, replace '*.html' with your proper search string. Then, it executes the perl script sub.pl (from the tutorial linked above), passing into it the current file name being found via the >{} parameter. The >\; signifies that this is the end of the statement to be executed on the results of >find. The perl parameters >-pi -0777 allow the script to be ran on the actual files passed into as parameters and save the output back into the files, while also treating whitespace and breaks in a manner compatible with the regular expression searching for the multiple line string.
About
the Author:
Mike Marr is a staff writer WebProNews.
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