Differences between revisions 10 and 11
⇤ ← Revision 10 as of 2014-04-22 01:27:12 →
Size: 1458
Editor: GreyCat
Comment: fix dodgy example; refer to FAQ 106
← Revision 11 as of 2015-03-05 00:29:41 → ⇥
Size: 1502
Editor: izabera
Comment: syntax hl
Deletions are marked like this. Additions are marked like this.
Line 5: Line 5:
{{{
    date > file		 {{{#!highlight bash
date > file
Line 10: Line 10:
{{{
    date 2> file		 {{{#!highlight bash
date 2> file
Line 15: Line 15:
{{{
    date > file 2>&1		 {{{#!highlight bash
date > file 2>&1
Line 20: Line 20:
{{{
    # Bash only. Equivalent to date > file 2>&1 but non-portable.
    date &> file		 {{{#!highlight bash
# Bash only. Equivalent to date > file 2>&1 but non-portable.
date &> file
Line 26: Line 26:
{{{
    for i in "${list[@]}"; do
     echo "Now processing $i"
        # more stuff here...
    done > file 2>&1		 {{{#!highlight bash
for i in "${list[@]}"; do
    echo "Now processing $i"
    # more stuff here...
done > file 2>&1
Line 35: Line 35:
{{{
    # redirect both standard output and standard error to "log.txt"
    exec > log.txt 2>&1
    # all output including stderr now goes into "log.txt"		 {{{#!highlight bash
# redirect both standard output and standard error to "log.txt"
exec > log.txt 2>&1
# all output including stderr now goes into "log.txt"
Line 45: Line 45:
{{{
    {
     date
     # some other commands
        echo done
    } > messages.log 2>&1		 {{{#!highlight bash
{
    date
    # some other commands
    echo done
} > messages.log 2>&1

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)