E-learning module "Linux Basics"

Combinations of Commands

| → pipe. This can be used to forward the output of a command as input for another. 

$ history | sort | less → forward the output of history to sort. Then forward the sorted output as input to less.

 
 

Linux has three standard in- or output handles:
  • stdout → Standard output (e.g. the monitor).
  • stdin   → Standard input (e.g. the keyboard or a file).
  • stderr → Standard error output.

 
 

Instead of forwarding output to another command using |, the output can be redirected into a file:
  • >       → Redirect stdout into a file. The file is either generated or overwritten.  
  • 2>     → Redirect stderr into a file. The file is either generated or overwritten.  
  • 2>&1 → Redirect stdout and stderr into a file. The file is either generated or overwritten.  
  • >>     → Redirect output and append to a file.
  • <       → Redirect the input.

$ history | sort >> filename.txt → Append the sorted output of the command history to the file filename.txt.
$ nano -w filename.txt → Edit filename.txt.

 
 

Commands can be run in a sequence, depending on the result of the preceeding command:
  • && → Execute the subsequent command if the preceeding command was executed successfully.
  • || → Execute the subsequent command if the preceeding command failed.
  • ;   → Execute the commands in a sequence, no matter what the results are.

 
 

$ tee → The output of a command can be forwarded simultaneously into a file and to standard output.

$ history | sort | tee sortiert.txt | less  → Redirect the sorted command history into file sortiert.txt and forward it to less.

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