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Top Forums Shell Programming and Scripting Sed: would like to return an error for empty string Post 303045785 by bedtime on Monday 13th of April 2020 09:00:26 AM
Old 04-13-2020
Sed: would like to return an error for empty string

There are actually two things that I want to do:

1. Detect if there is a 3 digit number and if so return an error (working)
2. Detect if there is an empty string and return an error if so (not working)

I would like to do 1 & 2 using the sed command only once; I'm trying to do things correctly and efficiently.

I have so far:
Code:
echo "" | sed -n -r '/[0-9]{3}/{q100}; //{q100}'; echo $?

(For newbies: -n quiets text output, -r allows for GNU program to do true regex, {q100} returns error '100', '$?' is the last returned result)



The result is 0, which is not what I want as the string is empty. My attempt is the portion '//{q100}', but I can see that it is difficult to test against nothing-quite perplexing actually.
 

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echo(1) 						      General Commands Manual							   echo(1)

NAME
echo - echo (print) arguments SYNOPSIS
[arg] ... DESCRIPTION
writes its arguments separated by blanks and terminated by a new-line on the standard output. It also understands C-like escape conven- tions; beware of conflicts with the shell's use of write an alert character backspace print line without appending a new-line form-feed new-line carriage return tab vertical tab backslash the 8-bit character whose ASCII code is the 1-, 2-, 3- or 4-digit octal number n, whose first character must be a zero. write an 8-bit value that is the zero-, one-, two- or three-digit octal number num is useful for producing diagnostics in command files and for sending known data into a pipe. Notes Berkeley differs from this implementation. The former does not implement the backslash escapes. However, the semantics of the escape can be obtained by using the option. The echo command implemented as a built-in function of follows the Berkeley semantics (see csh(1)). EXTERNAL INFLUENCES
Environment Variables determines the interpretation of arg as single and/or multi-byte characters. If is not specified in the environment or is set to the empty string, the value of is used as a default for each unspecified or empty vari- able. If is not specified or is set to the empty string, a default of "C" (see lang(5)) is used instead of If any internationalization variable contains an invalid setting, behaves as if all internationalization variables are set to "C". See environ(5). International Code Set Support Single- and multi-byte character code sets are supported. AUTHOR
was developed by OSF and HP. SEE ALSO
sh(1). BUGS
No characters are printed after the first This is not normally a problem. STANDARDS CONFORMANCE
echo(1)
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