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Full Discussion: Single quote _error_.
Top Forums Shell Programming and Scripting Single quote _error_. Post 303027734 by Don Cragun on Saturday 22nd of December 2018 03:19:55 PM
Old 12-22-2018
Expanding on what RudiC has already said and replying to wisecracker's comment that this question is in my domain... If you're trying to write portable code, DO NOT use echo if you intend to invoke it with a first argument starting with <minus-sign> (-), with -- as an argument, or if any argument contains a <backslash> character (\).

The synopsis for echo in the standards is echo [string...] and the options section for echo in the standards says:
Code:
The echo utility shall not recognize the "--" argument in the manner specified by Guideline 10
of XBD Section 12.2 (on page 216); "--" shall be recognized as a string operand.

Implementations shall not support any options.

And then, unlike the description of any other utility in the standards, the description of the string operand is:
Code:
	string	A string to be written to standard output. If the first operand is -n, or if any of the
		operands contain a <backslash> character, the results are implementation-defined.

XSI		On XSI-conformant systems, if the first operand is -n, it shall be treated as a string,
		not an option. The following character sequences shall be recognized on XSI-conformant
		systems within any of the arguments:

		\a	Write an <alert>.

		\b	Write a <backspace>.

		\c	Suppress the <newline> that otherwise follows the final argument in the
			output. All characters following the '\c' in the arguments shall be
			ignored.

		\f	Write a <form-feed>.

		\n	Write a <newline>.

		\r	Write a <carriage-return>.

		\t	Write a <tab>.

		\v	Write a <vertical-tab>.

		\\	Write a <backslash> character.

		\0num	Write an 8-bit value that is the zero, one, two, or three-digit octal number
			num.

Except for the first paragraph of the above quote, this section is shaded and has an XSI margin tag which means that it applies only on systems that support the standard's XSI option (which means that the system supports all of the optional requirements needed for UNIX brand certification by The Open Group in addition to meeting all of the requirements needed for POSIX certification by the IEEE).
Last edited by Don Cragun; 01-06-2019 at 09:56 AM.. Reason: Fix typos: s/−/-/g
These 3 Users Gave Thanks to Don Cragun For This Post:
Neo rbatte1 wisecracker
 

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