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Top Forums Shell Programming and Scripting What is the meaning of ## in UNIX shell script? Post 302988664 by RavinderSingh13 on Friday 30th of December 2016 01:54:32 PM
Old 12-30-2016
Hello shuklajayb4,

Welcome to forums, hope you will enjoy learning here. It is called Parameter expansion, when you do a man bash you could see the following.
Quote:
${parameter##word}
Remove matching prefix pattern. The word is expanded to produce a pattern just as in pathname expansion. If the pattern matches the
beginning of the value of parameter, then the result of the expansion is the expanded value of parameter with the shortest matching pat-
tern (the ‘‘#’’ case) or the longest matching pattern (the ‘‘##’’ case) deleted. If parameter is @ or *, the pattern removal operation
is applied to each positional parameter in turn, and the expansion is the resultant list. If parameter is an array variable subscripted
with @ or *, the pattern removal operation is applied to each member of the array in turn, and the expansion is the resultant list.
Here is an example of same too.
So let's say we have following string into a variable.
Code:
MYSTRING="Be liberal in what you accept, and conservative in what you send"

So here is the use of # and ##.
Code:
${MYSTRING#* }	Be liberal in what you accept, and conservative in what you send
${MYSTRING##* }	Be liberal in what you accept, and conservative in what you send

As you could see above(selected text will not be shown) # is removing the text till very first space and on other hand ## is printing the text till very last(maximum) match of space. I hope this helps you.

Thanks,
R. Singh
These 2 Users Gave Thanks to RavinderSingh13 For This Post:
 

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fnmatch(3C)						   Standard C Library Functions 					       fnmatch(3C)

NAME
fnmatch - match filename or path name SYNOPSIS
#include <fnmatch.h> int fnmatch(const char *pattern, const char *string, int flags); DESCRIPTION
The fnmatch() function matches patterns as described on the fnmatch(5) manual page. It checks the string argument to see if it matches the pattern argument. The flags argument modifies the interpretation of pattern and string. It is the bitwise inclusive OR of zero or more of the following flags defined in the header <fnmatch.h>. FNM_PATHNAME If set, a slash (/) character in string will be explicitly matched by a slash in pattern; it will not be matched by either the asterisk (*) or question-mark (?) special characters, nor by a bracket ([]) expression. If not set, the slash character is treated as an ordinary character. FNM_NOESCAPE If not set, a backslash character () in pattern followed by any other character will match that second character in string. In particular, "\" will match a backslash in string. If set, a backslash character will be treated as an ordinary character. FNM_PERIOD If set, a leading period in string will match a period in pattern; where the location of "leading" is indicated by the value of FNM_PATHNAME: o If FNM_PATHNAME is set, a period is "leading" if it is the first character in string or if it immediately fol- lows a slash. o If FNM_PATHNAME is not set, a period is "leading" only if it is the first character of string. If not set, no special restrictions are placed on matching a period. RETURN VALUES
If string matches the pattern specified by pattern, then fnmatch() returns 0. If there is no match, fnmatch() returns FNM_NOMATCH, which is defined in the header <fnmatch.h>. If an error occurs, fnmatch() returns another non-zero value. USAGE
The fnmatch() function has two major uses. It could be used by an application or utility that needs to read a directory and apply a pattern against each entry. The find(1) utility is an example of this. It can also be used by the pax(1) utility to process its pattern operands, or by applications that need to match strings in a similar manner. The name fnmatch() is intended to imply filename match, rather than pathname match. The default action of this function is to match file- names, rather than path names, since it gives no special significance to the slash character. With the FNM_PATHNAME flag, fnmatch() does match path names, but without tilde expansion, parameter expansion, or special treatment for period at the beginning of a filename. The fnmatch() function can be used safely in multithreaded applications, as long as setlocale(3C) is not being called to change the locale. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |CSI |Enabled | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe with exceptions | +-----------------------------+-----------------------------+ SEE ALSO
find(1), pax(1), glob(3C), setlocale(3C), wordexp(3C), attributes(5), fnmatch(5), standards(5) SunOS 5.10 24 Jul 2002 fnmatch(3C)
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