Piping

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You can mix commands to do certain things.

 dmesg | grep hd

That will search dmesg and try to find the string "hd". Now piping is extremely useful. Another example of a pipe:

 dmesg | less

Now this command you can see the dmesg fully and is easier to read.

You can also make longer 'pipelines' by using a pipe of several commands. For instance, to browse the last fifty lines of dmesg:

 dmseg | tail -50 | less

Redirection:

This will save the dmesg information in your home directory in the file log.txt

 dmesg > ~/log.txt

You can also redirect only the stdout by using '1>' or only the stderr by using '2>'.

For instance, if you want to run a command that gives a lot of junk as output, and you just want to see any errors, you can redirect the output to the null device (/dev/null):

 mplayer /path/to/movie.avi 1> /dev/null

You can also use the > and >> to cat stdin into a new or existing file:

 bash-3.1$ cat > newFile
 This is a new file            
 you can type text here and it
 get's redirected to the file newFile
 ctrl-c exits
  • Warning
  • cat > fileThatAlreadExists WILL OVERWRITE THE FILE! be careful :-)

You can use cat to check the text you just added:

 bash-3.1$ cat newFile 
 This is a new file 
 you can type text here and it
 get's redirected to the file newFile
 ctrl-c exits
 

Now that a file is created you can add to it with the >> operator

 bash-3.1$cat >> newFile
 This is a new line to add to newFile

And if you use cat again to read the file

 bash-3.1$cat newFile
 This is a new file 
 you can type text here and it
 get's redirected to the file newFile
 ctrl-c exits
 This is a new line to add to newFile