The Perl languages borrow features from other programming languages including C, shell script (sh), AWK, and sed; Wall also alludes to BASIC and Lisp in the introduction to "Learning Perl" (Schwartz & Christiansen) and so on. They provide text processing facilities without the arbitrary data-length limits of many contemporary Unix command line tools, facilitating manipulation of text files. Perl 5 gained widespread popularity in the late 1990s as a CGI scripting language, in part due to its unsurpassed regular expression and string parsing abilities.