Piping both stdout and stderr in bash?

by

(Note that &>>file appends to a file while &> would redirect and overwrite a previously existing file.)

To combine stdout and stderr you would redirect the latter to the former using 1>&2. This redirects stdout (file descriptor 1) to stderr (file descriptor 2), e.g.:

$ { echo "stdout"; echo "stderr" 1>&2; } | grep -v std
stderr
$

stdout goes to stdout, stderr goes to stderr. grep only sees stdout, hence stderr prints to the terminal.

On the other hand:

$ { echo "stdout"; echo "stderr" 1>&2; } 2>&1 | grep -v std
$

After writing to both stdout and stderr, 2>&1 redirects stderr back to stdout and grep sees both strings on stdin, thus filters out both.

You can read more about redirection here.

Regarding your example (POSIX):

cmd-doesnt-respect-difference-between-stdout-and-stderr 2>&1 | grep -i SomeError

or, using >=bash-4:

cmd-doesnt-respect-difference-between-stdout-and-stderr |& grep -i SomeError

More Related Contents:

  1. How to redirect and append both standard output and standard error to a file with Bash
  2. How can I pipe stderr, and not stdout?
  3. Redirect stderr and stdout in Bash [duplicate]
  4. Bash script – store stderr in a variable [duplicate]
  5. How to redirect both stdout and stderr to a file [duplicate]
  6. Shell redirection i/o order
  7. Capture both stdout and stderr in Bash [duplicate]
  8. How to store standard error in a variable
  9. Bash how do you capture stderr to a variable? [duplicate]
  10. Why piping input to “read” only works when fed into “while read …” construct? [duplicate]
  11. How to store the output of a command in a variable at the same time as printing the output?
  12. How to pipe stdout while keeping it on screen ? (and not to a output file)
  13. How do file descriptors work?
  14. How to redirect a program that writes to tty?
  15. Why start a shell command with a backslash?
  16. How to delete files older than X hours
  17. How can I reference a file for variables using Bash?
  18. Why is this bash prompt acting strangely/disappearing, and how do I fix it (OS X)?
  19. Use awk to find average of a column [duplicate]
  20. Bash: Copy named files recursively, preserving folder structure
  21. Read a variable in bash with a default value
  22. Pipe, standard input and command line arguments in Bash
  23. What does “export” do in shell programming? [duplicate]
  24. What is the most elegant way to remove a path from the $PATH variable in Bash?
  25. How can I convert tabs to spaces in every file of a directory?
  26. Multiple commands in an alias for bash
  27. How do I redirect stderr and stdout to file for a Ruby script?
  28. How to match a single quote in sed
  29. Read n lines at a time using Bash
  30. Difference between $stdout and STDOUT in Ruby

Leave a Comment