Pipes in Linux/Unix

Command pipeline

• The output of 1 command is directed to the input of the another to form a pipeline.
  A pipe is used by the shell to connect the stdout of one command directly to the stdin of another command.
  Example
  
  
• STDERR is not passed down the pipe (BY Default)

• The symbol for a pipe is the vertical bar ( | ). The command syntax is:

 

     command1 [arguments]  |  command2 [arguments]

• Pipes accomplish with one command what otherwise would take intermediate files and multiple commands. For example, operation 1 and operation 2 are equivalent:

 

Operation 1

     who > temp

     sort temp



Operation 2

     who | sort

• Pipes do not affect the contents of the input files.
• Two very common uses of a pipe are with the "more" and "grep" utilities. Some examples:

   
  
       ls -al | more
  
       who | more
  
       ps ug | grep myuserid
  
       who | grep  kelly
  
  

• Diverting stream through tee
  tee enables the stream to be diverted.
  Example:
  ls | tee somefile | sort | more
  
  

Building commands

• Shells provide glue to build complex commands

References

• http://www.cis.rit.edu/class/simg211/