Perl substitute - the e modifier

For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

Here's a graphic illustration of the use of the "e" for "execute" modifier used on the end of substitute operation in Perl.

The "s" for substitute allows you to replace a matched pattern with a STRING in which you can use special references like \1 or $1 for the first matched substring. If you want it to replace the matched pattern with the RESULT OF RUNNING CODE, you should add that extra e on the end.

In this example, the $emma variable ends up containing a corrupted email address which actually includes some code, whereas (with the "e"), the $emily variable results in a correct email address with the section before the "@" pushed to lower case.

$emma = 'Graham@wellho.net';

$emily = 'Graham@wellho.net';

 

$emma =~ s/(\w+)@/lc($1)."@"/;

$emily =~ s/(\w+)@/lc($1)."@"/e;

 

print ("$emma\n$emily\n");

 

__END__

 

Dorothy:plpw grahamellis$ perl swithe

lc(Graham)."@"wellho.net

graham@wellho.net

Dorothy:plpw grahamellis$

(written 2008-12-16)

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