> >> |

Redirecting output

Any program or command that produces textual output to the screen (called standard output) can be simply directed to put that text into a file instead of onto the screen. Or, using the character ``|'', it can be passed directly to another command.

>
Use the character `>' (``right arrow'', or ``right angle bracket'', or ``greater than'') followed by a filename, after a command to create a new file with the results of the command. Example:

spell mydoc > error.dat -- spellchecks the file `mydoc', putting the list of misspelled words into `error.dat'
myprog > data/0112.dat -- runs the program `myprog', and directs all output into the file `0112.dat' located in the subdirectory data
myprog > /dev/null -- runs the program `myprog', and directs all output into the famous Unix ``black hole'' file. /dev/null is where to send output which you don't need and don't want cluttering up a file or the screen

WARNING: If file bbb already exists, and you command myprog > bbb, then the old file bbb will be deleted and replaced by the output of the command `myprog'.

>>
If you want to append text output to an existing file -- without destroying its existing contents! -- then use double arrows, >>. Examples:

spell mydoc >> error.dat -- spellchecks the file `mydoc', adding the list of misspelled words onto the end of pre-existing file `error.dat'
myprog >> data/0112.dat -- runs the program `myprog', and directs all output onto the end of pre-existing file `0112.dat' located in the subdirectory data

|
Using |, the output from a command can be piped directly into another command. Examples:

spell mydoc | more -- displays the misspelled words in `mydoc' -- but only one screenful at a time
spell mydoc | wc -l -- counts the number of misspelled words in `mydoc'
grep help mydoc | wc -l -- counts how many lines in `mydoc' contain the string "help"
grep -hi smith *.dat | sort | more -- extract all the lines in the files *.dat containing the string "smith" (case insensitive); sort them alphabetically, and display the results one screenful at a time