Redirection (Linux) - Revision history

Christoph: /* Redirecting to and from the standard file handles */

2020-09-22T20:29:51Z

‎Redirecting to and from the standard file handles

2020-09-22T20:27:30Z

‎Redirecting with tee

2017-02-28T19:34:31Z

‎Redirecting to and from the standard file handles

2016-04-08T23:55:34Z

2015-08-28T21:28:56Z

‎Swapping STDOUT and STDERR using file descriptors

2015-03-06T21:24:56Z

‎Redirecting to and from the standard file handles

2015-03-06T20:52:30Z

‎External links

2015-03-06T20:50:27Z

‎EOF

2015-03-06T20:46:36Z

‎Swapping STDOUT and STDERR using file descriptors

2014-01-23T04:16:33Z

@@ Line 63: / Line 63: @@
   command1 2> file1
-executes <tt>command1</tt>, directing the [[standard error]] stream to <tt>file1</tt> (useful since standard error outputs to the terminal by default and is unaffected by redirection unless so specified).
+executes <tt>command1</tt>, directing the [[stderr|standard error]] stream to <tt>file1</tt> (useful since standard error outputs to the terminal by default and is unaffected by redirection unless so specified).
 In shells derived from csh (the [[C shell]]), the syntax instead appends the <tt>&</tt> character to the redirect characters, thus achieving a similar result.
-Another useful capability is to redirect one standard file handle to another. The most popular variation is to merge [[standard error]] into [[standard output]] so error messages can be processed together with (or alternately to) the usual output. Example:
+Another useful capability is to redirect one standard file handle to another. The most popular variation is to merge [[stderr|standard error]] into [[stdout|standard output]] so error messages can be processed together with (or alternately to) the usual output. Example:
   find / -name .profile > results 2>&1

← Older revision		Revision as of 20:27, 22 September 2020
Line 22:		Line 22:

	The "<code>>(...)</code>" (process substitution) part creates a FIFO and lets tee listen on it. Then, it uses > (file redirection) to redirect the STDOUT of command to the FIFO that your first tee is listening on.		The "<code>>(...)</code>" (process substitution) part creates a FIFO and lets tee listen on it. Then, it uses > (file redirection) to redirect the STDOUT of command to the FIFO that your first tee is listening on.
		+
		+	* Other methods:
		+	<pre>
		+	$ ./a.out 2>&1 \| tee output
		+	#~OR~
		+	$ ./a.out \|& tee output
		+	</pre>

	== Piping ==		== Piping ==

@@ Line 72: / Line 72: @@
 * Find all "<code>*.txt</code>" files under the <code>/etc</code> directory and suppress any "Permission denied" messages:
   find /etc -name '*.txt' |& grep -v "Permission denied"
 ===EOF===

@@ Line 16: / Line 16: @@
   command1 < infile > outfile
 combines the two capabilities: <tt>command1</tt> reads from <tt>infile</tt> and writes to <tt>outfile</tt>
 == Piping ==

@@ Line 156: / Line 156: @@
   $ ls -l /proc/self/fd
-* Check that "<code>3<&1</code>" is the same as "<code>3>&1</code>":
+* Check that "<code>3<&1</code>" is the same as "<code>3>&1</code>" (see: <code>`[[strace]]`</code>):
   $ sudo strace -f -s 200 -e trace=dup2 sh -c 'exec 3<&1'
   dup2(1, 3)                              = 3

@@ Line 44: / Line 44: @@
 | ([[Stderr|stderr]]) || standard error
 |}
 For example:

@@ Line 242: / Line 242: @@
 ==External links==
 *[http://tldp.org/LDP/abs/html/ Advanced Bash-Scripting Guide]
 *[http://www.linuxdevcenter.com/pub/a/linux/lpt/13_01.html Using Standard Input and Output]

@@ Line 71: / Line 71: @@
   line2
   EOF
 ===Redirection order priorities===

@@ Line 146: / Line 146: @@
 One can list the open file descriptors with
   $ ls -l /proc/self/fd
 == Chained pipelines ==

@@ Line 3: / Line 3: @@
 In Unix-like systems, there are two output paths that, if left unmodified, will send output to your screen. Standard output (STDOUT) captures the normal output of a given command. Standard error (STDERR) captures most failures and error conditions.
 To pass the permission denied message in the stderr to the same output stream as "regular output" you must combine the two. In your example, in order for your grep -v to properly operate on it, you combine stdout (standard output) and stderr with the arcane syntax you see.
 == Redirecting standard input and standard output ==
@@ Line 69: / Line 64: @@
 * Find all "<code>*.txt</code>" files under the <code>/etc</code> directory and suppress any "Permission denied" messages:
   find /etc -name '*.txt' |& grep -v "Permission denied"
 ===Redirection order priorities===