Regular expressions should be familiar as they are used in many UNIX commands with grep as best known
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grep pattern file; # Prints out each line of file containing pattern
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The rules for pattern are rich and we will discuss later -- consider here the simple pattern Fox
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Then we can write the PERL version of grep as follows:
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$line =0;
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while (<>) {
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if( /Fox/ ) { # Generalize to /Pattern/ to test positive if Pattern in $_
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print $line, "$_"; } # $_ is current line by default
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$line++; }
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Another familiar operator should be s in sed (the batch or stream line editor) where
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s/Pattern1/Pattern2/; # substitutes Pattern1 by Pattern2 in each line
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The same command can be used in PERL with again substitution occuring on $_
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