title: grepping using the "|" alternative operator
body: <p>The following is a sample of a large file named AT5G60410.gff:</p>
  
  <pre><code>Chr5    TAIR10  gene    24294890    24301147    .   +   .   ID=AT5G60410;Note=protein_coding_gene;Name=AT5G60410
  Chr5    TAIR10  mRNA    24294890    24301147    .   +   .   ID=AT5G60410.1;Parent=AT5G60410;Name=AT5G60410.1;Index=1
  Chr5    TAIR10  protein 24295226    24300671    .   +   .   ID=AT5G60410.1-Protein;Name=AT5G60410.1;Derives_from=AT5G60410.1
  Chr5    TAIR10  exon    24294890    24295035    .   +   .   Parent=AT5G60410.1
  Chr5    TAIR10  five_prime_UTR  24294890    24295035    .   +   .   Parent=AT5G60410.1
  Chr5    TAIR10  exon    24295134    24295249    .   +   .   Parent=AT5G60410.1
  Chr5    TAIR10  five_prime_UTR  24295134    24295225    .   +   .   Parent=AT5G60410.1
  Chr5    TAIR10  CDS 24295226    24295249    .   +   0   Parent=AT5G60410.1,AT5G60410.1-Protein;
  Chr5    TAIR10  exon    24295518    24295598    .   +   .   Parent=AT5G60410.1
  </code></pre>
  
  <p>I am having some trouble extracting specific lines from this using grep.  I wanted to extract all lines that are of type "gene" or type "exon", specified in the third column. I was suprised when this did not work:</p>
  
  <pre><code>grep 'gene|exon' AT5G60410.gff
  </code></pre>
  
  <p>No results are returned. Where have I gone wrong?</p>