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Full Discussion: Understanding Xargs
Top Forums Shell Programming and Scripting Understanding Xargs Post 303010124 by RudiC on Wednesday 27th of December 2017 05:24:23 AM
Old 12-27-2017
Now, these are very basic questions from quite broad a range of IT, and I'm not sure I can cover that to satisfaction. On top, there may be a language barrier, e.g with "occurrence". I'd advise to use a dictionary, as - to me - the meaning got immediately clear when seeing the translations. Please also consult introductory text books and / or man pages.

It might be worthwhile to internalize the concept of a string which you will encounter everywhere in IT (tools, databases, documents, files, ...) when needing to represent text. It can come in a variety of shapes, like fixed or varying length strings, zero terminated or with a leading length indicator, string constants, substrings, string concatenations, and what have you, and there are many tools, libraries, functions to handle them. Different digital items (numbers, logical values) can be output to screen as readable text representations only, not as the individual items themselves.

Then, there are text files, a loosely structured collection of (mostly) printable characters. In *nix systems, those consist of lines of characters terminated by a <new line> (\n, ^J, 0x0A) character. But this is not the only possible text representation. When reading a line from a file, you can put it into a single string variable, or split it into several substrings. If you do so by applying spaces and / or punctuation chars for separating, the substrings will be words. But any other separation is possible albeit not necessarily sensible. So, a line is sort of a superset of (a group of) strings.

A "command line" specifies a collection of a command name (perhaps including a path), zero or more options (with possible arguments), and zero or more parameters. Any of those is a (possibly one character) string, analysed by the command interpreter, and then supplied to the program being executed. Please be aware that the terms "argument" and "parameter" are not strictly distinguished between and both are loosely and interchangably used. (I neglected possible local variable assingments and redirections to avoid overcomplicaton.)

Last edited by RudiC; 12-27-2017 at 10:13 AM.. Reason: Some typos
 

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nl(1)							      General Commands Manual							     nl(1)

Name
       nl - line numbering filter

Syntax
       nl [-h type] [-b type] [-f type] [-v start#] [-i incr] [-p ] [-l num] [-s sep] [-w width] [-n format] [-d delim] file

Description
       The  command reads lines from the named file or from the standard input, if no file is named, and reproduces the lines on the standard out-
       put.  Lines are numbered on the left in accordance with the command options in effect.

       The command views the text it reads in terms of logical pages.  Line numbering is reset at the start of each logical page.  A logical  page
       consists  of  a header, a body, and a footer section.  Empty sections are valid.  Different line numbering options are independently avail-
       able for header, body, and footer.  For example, you can elect not to number header and footer lines while numbering  blank  lines  in  the
       body.

       The start of logical page sections is signaled by input lines containing nothing but the following delimiter characters:

		 Line contents	Start of

		 ::: 	header

		 ::		body

		 :		footer

       Unless otherwise specified, assumes that the text it is reading is in the body of a single logical page.

Options
       Command options may appear in any order and may be intermingled with an optional file name.  Only one file may be named.

       -b type		   Specifies  which  logical page body lines are to be numbered.  The following are recognized types and their meaning: a,
			   number all lines; t, number lines with printable text only; n, no line numbering; pstring, number only lines that  con-
			   tain the regular expression specified in string.

			   The default type for logical page body is t (text lines numbered).

       -h type		   Same as -b type except for header.  Default type for logical page header is n (no lines numbered).

       -f type		   Same as -b type except for footer.  Default for logical page footer is n (no lines numbered).

       -p		   Do not restart numbering at logical page delimiters.

       -v start#	   The initial value used to number logical page lines.  Default is 1.

       -i incr		   The increment value used to number logical page lines.  Default is 1.

       -s sep		   The character used in separating the line number and the corresponding text line.  Default sep is a tab.

       -w width 	   The number of characters used for the line number.  Default width is 6.

       -n format	   The	line  numbering  format.   Recognized values are the following: ln, left justified, leading zeroes suppressed; rn,
			   right justified, leading zeroes suppressed; rz, right justified, leading zeroes kept.  Default format is rn (right jus-
			   tified).

       -l num		   The	number	of  blank lines to be considered as one.  For example, -l2 results in only the second adjacent blank being
			   numbered (if the appropriate -ha, -ba, or -fa option is set).  Default is 1.

       -d xx		   The delimiter characters specifying the start of a logical page section may be changed from the default characters (:)
			   to two user-specified characters.  If only one character is entered, the second character remains the default character
			   (:).  No space should appear between the -d and the delimiter characters.  To enter a  backslash,  you  must  type  two
			   backslashes (//).

Examples
       nl -v10 -i10 -d!+ file1
       This command numbers file1 starting at line number 10 with an increment of ten.	The logical page delimiters are !+.

See Also
       pr(1)

																	     nl(1)
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