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Top Forums Shell Programming and Scripting Need Quick help on Understanding sed Regex Post 302926413 by Nandy on Monday 24th of November 2014 08:20:10 AM
Old 11-24-2014
Need Quick help on Understanding sed Regex

Hi Guys,

Could you please kindly explain what exactly the below SED command will do ?

I am quite confused and i assumed that,
Code:
sed 's/[ \t]*$/ /'

1. It will remove tab and extra spaces .. with single space.

The issue is if it is removing tab then it should be Î right ..
please assist.


Moderator's Comments:
Mod Comment Please use code tags next time for your code and data. Thanks

Last edited by vbe; 11-24-2014 at 09:55 AM..
 

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vis(1)							      General Commands Manual							    vis(1)

NAME
vis, inv - make unprintable and non-ASCII characters in a file visible or invisible SYNOPSIS
file ... file ... DESCRIPTION
reads characters from each file in sequence and writes them to the standard output, converting those that are not printable or not ASCII into a visible form. inv performs the inverse function, reading printable characters from each file, returning them to non-printable or non-ASCII form, if appropriate, then writing them to standard output; Non-printable ASCII characters are represented using C-like escape conventions: backslash backspace escape form-feed new-line carriage return space horizontal tab vertical tab the character whose ASCII code is the 3-digit octal number n. the character whose ASCII code is the 2-digit hexadecimal number n. Non-ASCII single- or multi-byte characters are examined one byte at a time. For each byte, if it can be displayed as an ASCII character, it is treated as if it is an ASCII character; Otherwise, it is represented in the following conventions: the 8-bit character whose code value is the 3-digit octal number n. the 8-bit character whose code value is the 2-digit hexadecimal number n. Space, horizontal-tab, and new-line characters can be treated as printable (and therefore passed unaltered to the output) or non-printable depending on the options selected. Backslash, although printable, is expanded by vis, to a pair of backslashes so that when they are passed back through inv, they convert back to a single backslash. If no input file is given, or if the argument is encountered, and inv read from the standard input. Options and recognize the following options: Treat new-line, space, and horizontal tab as non-printable characters. expands them visibly as and rather than passing them directly to the output. discards these characters, expecting only the printable expansions. New-line characters are inserted by every 16 bytes so that the output will be in a form that is usable by most editors. Make and silent about non-existent files, identical input and output, and write errors. Normally, no input file can be the same as the output file unless it is a special file. Treat horizontal-tab and space characters as non-printable in the same manner that treats them. Cause output to be unbuffered (byte-by-byte); normally, output is buffered. Cause output to be in hexadecimal form rather than the default octal form. Either form is accepted to as input. EXTERNAL INFLUENCES
Environment Variables determines the language in which messages are displayed. International Code Set Support Single- and multi-byte character code sets are supported. WARNINGS
Redirecting output to an input file destroys the original data. Therefore, command forms such as should be avoided unless the source file can be safely discarded. AUTHOR
was developed by HP. SEE ALSO
cat(1), echo(1), od(1). vis(1)
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