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Top Forums Shell Programming and Scripting How to change only the x first characters of a string? Post 302137777 by Juha on Thursday 27th of September 2007 02:14:20 AM
Old 09-27-2007
How to change only the x first characters of a string?

Hi,

How can I replace x first characters from a string?
I have a file with... say 10000 entries as follows:

00123456781
00123456782
00123456783
...

What I want to do is change the leading "00" with for example "12"

The leading 00 can be in some files some other 1 or more digits e.g. "1" or "123" or what ever.

What would be the most efficient way of doing this as there might be even 20.000.000 entries in one file.

I wonder if the method could be embedded to a oneliner such as:

perl -i -p -e "s/old/new/g" filename

Thanks!
 

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REMQUO(3)						   BSD Library Functions Manual 						 REMQUO(3)

NAME
remquo -- floating-point remainder and quotient function SYNOPSIS
#include <math.h> double remquo(double x, double y, int *quo); long double remquol(long double x, long double y, int *quo); float remquof(float x, float y, int *quo); DESCRIPTION
The remquo() functions compute the value r such that r = x - n*y, where n is the integer nearest the exact value of x/y. If there are two integers closest to x/y, n shall be the even one. If r is zero, it is given the same sign as x. This is the same value that is returned by the remainder() function. remquo() also calculates the lower seven bits of the integral quotient x/y, and gives that value the same sign as x/y. It stores this signed value in the object pointed to by quo. SPECIAL VALUES
remquo(x, y, quo) returns a NaN and raises the "invalid" floating-point exception if x is infinite or y is 0. VECTOR OPERATIONS
If you need to apply the remquo() function to SIMD vectors or arrays, using the following functions provided by the Accelerate.framework may give significantly better performance: #include <Accelerate/Accelerate.h> vFloat vremquo(vFloat x, vFloat y, vUInt32 *q); SEE ALSO
math(3), remainder(3) STANDARDS
The remquo() functions conform to ISO/IEC 9899:2011. BSD
December 11, 2006 BSD
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