Linux 12 - Streams, Pipes and Redirects

• - stdin
• - stdout
• - stderr
• - tee
• - xargs

stdin
stuff a program chews up

wc < file1.txt
some programs don’t accept data from stdin

stdout
stuff a program spits out

ls > ls.txt

ls 1> ls.txt

stderr
where a program complains

ls bob 2> ls.txt
redirects stderr to ls.txt

 

Both stdout and stderror go to the console

To keep a log you would like to:

ls >> ls.txt→ will append
ls bob 2>> ls.txt→ will append stderr

ls bob >> results.txt 2>> errors.txt→ redirects both to files
ls bob > output.txt 2>&1→ redirect stderr to stdout in the same place

pipes

not all applications support stdin from other applications

ls | grep 3

tee

- write a program see what is doing and write to a file

- read from std input and write to standard output and file

ls | tee output.txt

xargs

- ls | echo

echo does not accept input from ls

- ls | xargs echo

 

 

 

 

 

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