The first place to look is in perlfaq5. Anyhow, there are several ways to do it. The easiest is to

(((pseudocode)))
open, for reading, the file you want to change (input file)
open, for writing, a temp file.

until EOF {
     read a record from the input file.
          if you want to keep it
               write it to the temp file
}

replace the input file with the temp file
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If the file is small (ymmv), you can do something like this:

(((pseudocode)))

open input file for reading

slurp ENTIRE input file into array (@contents = <INFILE>)

close the input file

use grep to remove lines with trailing slashes from the array (@conten
+ts = grep { !/\/$/ } @contents)

open the input file for writing (this act will destroy the input file!
+)

write array into the file
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A couple of suggestions: first, test from a copy of the file you plan on doing this to. Second, study perlre and grep for hints. Third, beware of trailing white space.