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→KEY CONCEPTS
<span style="font-family:courier;font-weight:bold">tr 'a-z' 'A-Z' < words.txt<br>cat < abc.txt<br>sort < xyz.txt</span>
[[Image:stdin-symbol.png|thumb|right|250px|The '''standard input''' ('''stdin''') symbol that describes where a Unix/Linux command receives '''input''']]
'''Standard output''' ('''stdout''') describes where a command sends it's output.<br>In the examples below, output from a command is sent to the '''monitor''', unless it is sent to a '''regular file'''.<br>We will discuss another redirection technique called '''pipelines''' later.
<span style="font-family:courier;font-weight:bold">ls -l<br>ls -l > detailed-listing.txt<br>ls /bin >> output.txt</span>
[[Image:stdin-symbol.png|thumb|right|250px|The '''standard input''' ('''stdin''') symbol that describes where a Unix/Linux command receives '''input''']]
'''Standard Error''' ('''stderr''') describes where a command sends it's error messages.<br>In the examples below, error messages from a command are sent to a file or are redirected to a file that acts as a "garbage can".