Hello world/Standard error: Difference between revisions

{{task|Basic language learning}}{{selection|Short Circuit|Console Program Basics}}A common practice in computing is to send error messages to a different output stream than [[User Output - text|normal text console messages]]. The normal messages print to what is called "standard output" or "standard out". The error messages print to "standard error". This separation can be used to redirect error messages to a different place than normal messages.

Output:

Pipe through a shell command:

With ''gawk'', ''mawk'' and ''nawk'': a special feature associates "/dev/stderr" with standard error. The manuals of ''gawk'' and ''mawk'' describe this feature; ''nawk'' also has this feature.

Other implementations might try to open /dev/stderr as a file. Some Unix clones, like [[BSD]], have a /dev/stderr device node that duplicates standard error, so this code would still work. Some systems have no such device node, so this code would fail. We recommend "cat 1>&2", which is more portable, and works with any Unix clone.

The redirection operator <code>1>&2</code> causes all output on stream 1 (standard out) to be redirected to stream 2 (standard error). The redirection can be moved to the end of the line, too.

Start Factor in a terminal for this.

Normally standard error is associated with the unit 0 but this could be different for different vendors. Therefore since Fortran 2003 there's an intrinsic module which defines the parameter ERROR_UNIT.

Note that although this satisfies the task requirement, error/1 also raises an error condition.

Output:

In Objective-C one can use the standard C library and the stderr as in the C language; nonetheless a common way to output to stderr for logging purpose and/or error notification is the <tt>NSLog</tt> function, that works almost like <tt>fprintf(stderr, "...")</tt>, save for the fact that the format string is an NSString object, and it also prepends a timestamp.

The .error object is a proxy that delegates to a backing stream, so this might be redirected. By default, this delegates to the .stderr object, which can also be used directly.

Since PowerShell has a slightly different system of pipes and streams (to facilitate easy usage from a host application) the standard Write-Error cmdlet is mainly for sending annotated error messages to the host:

Note that this outputs more than just the message because behind the scenes it is an uncaught exception:

This version will work with any REXX under operating systems (hosts) that don't have (or support) either stream output,

<br>or don't have a specific &nbsp; '''STDERR''' &nbsp; output steam (or a method of writing to one), &nbsp; or have the &nbsp; '''stderr''' &nbsp; device driver

<br>disabled &nbsp; (the "driver" may be known as a different name), &nbsp; or if the REXX doesn't utilize or bypasses the &nbsp; '''stderr''' &nbsp; device

<br>driver. &nbsp; Some or all of the above restrictions generally refer to the older/legacy REXXes.

This version will work with those operating systems (hosts) that support stream output and a &nbsp; STDERR &nbsp; output

Run Basic runs in a browser. This opens a new browser window, or a tab in the case of Chrome and some others.

[[Category:Scala Implementations]]

This program requires at least 1 line of input. It changes the first line to "Goodbye, World!" and then prints the first line to standard error. It reads and ignores the remaining lines.

Output:

This requires <code>/dev/stderr</code>, a device node from [[BSD]] and some other Unix clones. This command works with both Bourne Shell and C Shell.

The terms "standard output" and "standard error" are not used, but it's

trivial to send messages to a variety of devices by specifying their

numbers. Normally messages are displayed on the text console, which is

device 0. Instead, this example sends the message to the (first) printer,

{{omit from|Applesoft BASIC}}

{{omit from|bc|Always prints to standard output.}}

{{omit from|Brainf***}}

{{omit from|dc|Always prints to standard output.}}

{{omit from|GUISS|Cannot customize error messages}}

{{omit from|Integer BASIC}}

{{omit from|TI-83 BASIC|Same reason as TI-89.}}

{{omit from|TI-89 BASIC|no analogue to stderr, unless you count graph display vs. program IO}}

{{omit from|Unlambda|No concept of standard error (or alternate output streams in general).}}

[[Category:Streams]]