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Full Discussion: How to perform multiple operations on a number before storing to a variable?
Top Forums Shell Programming and Scripting How to perform multiple operations on a number before storing to a variable? Post 302958576 by prodigious8 on Friday 23rd of October 2015 11:30:01 AM
Old 10-23-2015
How to perform multiple operations on a number before storing to a variable?
(I am using bash)
I have a command that will find the line number in a file by searching for a string where it exists.

Code:
linenumber=$(grep -n "string" $FILENAME | cut -d : -fi)

This returns the line number and removes the string. Now that I have the line number I want to subtract 4 from it and give me a new line number.

Code:
newlinenumber=$((linenumber - 4))

What I would like to do is find the line number and subtract by 4 BEFORE storing to the variable "linenumber" so I can avoid creating a new variable "newlinenumber" altogether. Essentially I want to combine the two with the idea pictured as follows:

Code:
linenumber=$(grep -n "string" $FILENAME | cut -d : -fi) | $((linenumber - 4))

I want to know the correct syntax to make this possible.
 

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LEARN ABOUT OPENSOLARIS

libbash

LIBBASH(7)							  libbash Manual							LIBBASH(7)

NAME

     libbash -- A bash shared libraries package.

DESCRIPTION

     libbash  is  a package that enables bash dynamic-like shared libraries. Actually its a tool for managing bash scripts whose functions you may
     want to load and use in scripts of your own.

     It contains a 'dynamic loader' for the shared libraries ( ldbash(1)), a configuration tool (ldbashconfig(8)), and some libraries.

     Using ldbash(1) you are able to load loadable bash libraries, such as getopts(1) and hashstash(1).  A bash shared library that can be  loaded
     using
     ldbash(1) must answer 4 requirments:

     1.     It must be installed in $LIBBASH_PREFIX/lib/bash (default is /usr/lib/bash).

     2.     It must contain a line that begins with '#EXPORT='.  That line will contain (after the '=') a list of functions that the library
	    exports.  I.e. all the function that will be usable after loading that library will be listed in that line.

     3.     It must contain a line that begins with '#REQUIRE='.  That line will contain (after the '=') a list of bash libraries that are
	    required for our library.  I.e. every bash library that is in use in our bash library must be listed there.

     4.     The library must be listed (For more information, see ldbashconfig(8)).

   Basic guidelines for writing library of your own:
     1.     Be aware, that your library will be actually sourced. So, basically, it should contain (i.e define) only functions.

     2.     Try to declare all variables intended for internal use as local.

     3.     Global variables and functions that are intended for internal use (i.e are not defined in '#EXPORT=') should begin with:
		  __<library_name>_
	    For example, internal function myfoosort of hashstash library should be named as
		  __hashstash_myfoosort
	    This helps to avoid conflicts in global name space when using libraries that come from different vendors.

     4.     See html manual for full version of this guide.

AUTHORS

     Hai Zaar <haizaar@haizaar.com>
     Gil Ran <ril@ran4.net>

SEE ALSO

     ldbash(1), ldbashconfig(8), getopts(1), hashstash(1) colors(1) messages(1) urlcoding(1) locks(1)

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