How can I redirect the output of multiple commands at once?

Redirecting the standard output of a single command is as easy as:

Toggle line numbers 
   1 date > file

To redirect standard error:

Toggle line numbers 
   1 date 2> file

To redirect both:

Toggle line numbers 
   1 date > file 2>&1

or, a fancier way:

Toggle line numbers 
   1 # Bash only.  Equivalent to date > file 2>&1 but non-portable.
   2 date &> file

Redirecting an entire loop:

Toggle line numbers 
   1 for i in "${list[@]}"; do
   2     echo "Now processing $i"
   3     # more stuff here...
   4 done > file 2>&1

However, this can become tedious if the output of many programs should be redirected. If all output of a script should go into a file (e.g. a log file), the exec command can be used:

Toggle line numbers 
   1 # redirect both standard output and standard error to "log.txt"
   2 exec > log.txt 2>&1
   3 # all output including stderr now goes into "log.txt"

(See FAQ 106 for more complex script logging techniques.)

Otherwise, command grouping helps:

Toggle line numbers 
   1 {
   2     date
   3     # some other commands
   4     echo done
   5 } > messages.log 2>&1

In this example, the output of all commands within the curly braces is redirected to the file messages.log.

More discussion

In-depth: Illustrated Tutorial

CategoryShell

BashFAQ/014 (last edited 2015-03-05 00:29:41 by izabera)