Diff for "BashFAQ/014"

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

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

    date > file

To redirect standard error:

    date 2> file

To redirect both:

    date > file 2>&1

or, a fancier way:

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

Redirecting an entire loop:

    for i in $list; do
        echo "Now processing $i"
        # more stuff here...
    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:

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

Otherwise, command grouping helps:

    {
        date
        # some other commands
        echo done
    } > 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

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