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→Additional File Manipulation Commands
<table cellpadding="5"><tr><th style="border-bottom: 1px solid black;text-align:left;">Linux Command</th><th style="border-bottom: 1px solid black;text-align:left;">Purpose</th></tr><tr valign="top"><td>'''cut'''</td><td>'''Used to extract fields and characters from records. The option '''-c''' option is used to cut by a character or a range of characters. The '''-f''' option indicates the field number or field range to display (this may require using the '''-d''' option to indicate the field separator (delimiter).'''<br><br>''Examples:''<br><span style="font-family:courier;font-weight:bold;">cut -f2 filename</span> - extract 2nd field from all records in file, using tab as delimiter (default)<br><span style="font-family:courier;font-weight:bold;">cut -d' ' -f2,5 filename</span> - extract 2nd and 5th field, using space as delimiter<br><span style="font-family:courier;font-weight:bold;">cut -d' ' -f1-3,5 filename</span> - extract 1st through 3rd and 5th fields, using space as delimiter<br><span style="font-family:courier;font-weight:bold;">cut -c3-5 filename</span> - extract 3rd to 5th characters</td></tr><tr valign="top"><td>'''tr'''</td><td>'''Used to translate characters to different characters.'''<br><br>''Examples:''<br><span style="font-family:courier;font-weight:bold;">tr a A < filename</span> - translate all characters "a" to "A"<br><span style="font-family:courier;font-weight:bold;">tr "[a-z]" "[A-Z]" < filename</span> - translate lowercase "a" through "z" to uppercase<br><span style="font-family:courier;font-weight:bold;">tr "a-z" "A-Z" < filename</span> - translate lowercase "a" through "z" to uppercase, different syntax (non-System V)<br><span style="font-family:courier;font-weight:bold;">tr ':' ' ' < filename</span> - translate all colons to spaces<br><span style="font-family:courier;font-weight:bold;">tr ' ' '\n' < filename</span> - translate all spaces to newline characters<br><span style="font-family:courier;font-weight:bold;">tr 'abc' 'A' < filename</span> - translate 'a', 'b', and 'c' to 'A', the last character in the "to" string repeats<br></td></tr><tr valign="top"><td><span style="font-family:courier;font-weight:bold;">wc</span></td><td>'''Displays various counts of the contents of a file.'''<br><br>''Examples:''<br><span style="font-family:courier;font-weight:bold;">wc -l filename</span> - displays number of lines in file<br><span style="font-family:courier;font-weight:bold;">wc -c filename</span> - displays number of characters in file<br><span style="font-family:courier;font-weight:bold;">wc -w filename</span> - displays number of words in fil<br></td></tr></table>
The /dev/null file (sometimes called the bit bucket or black hole) is a special system file that discards all data written into it
Useful to discard unwanted command output, for example:
find / -name "tempfile" 2> /dev/null
Also, /dev/null can provide null data (EOF only) to processes reading from it
Useful to purge (empty) files etc, for example: cat /dev/null > ~/.bashrc
===Piping (Using Pipes)===
