Single or double square brackets


 
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Old 10-01-2012
in bash try:
Code:
type [
type [[

They are both part of the shell: [ is a keyword like if, while, etc.: [[ is a shell builtin but still is treated a a word.

"word" is key here, because words are set off from each other by spaces or new lines.
[, ], [[, and ]] have to be set off from from other words by spaces or new lines.
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SQRT(3) 						   BSD Library Functions Manual 						   SQRT(3)

NAME
cbrt, cbrtf, cbrtl, sqrt, sqrtf, sqrtl -- cube root and square root functions LIBRARY
Math Library (libm, -lm) SYNOPSIS
#include <math.h> double cbrt(double x); float cbrtf(float x); long double cbrtl(long double x); double sqrt(double x); float sqrtf(float x); long double sqrtl(long double x); DESCRIPTION
The cbrt(), cbrtf(), and cbrtl() functions compute the cube root of x. The sqrt(), sqrtf(), and sqrtl() functions compute the non-negative square root of x. RETURN VALUES
The cbrt(), cbrtf(), and cbrtl() functions return the requested cube root. The sqrt(), sqrtf(), and sqrtl() functions return the requested square root unless an error occurs. An attempt to take the sqrt() of negative x raises an invalid exception and causes an NaN to be returned (except that the square root of -0 is valid and equal to -0.) SEE ALSO
fenv(3), math(3) STANDARDS
The cbrt(), cbrtf(), cbrtl(), sqrt(), sqrtf(), and sqrtl() functions conform to ISO/IEC 9899:1999 (``ISO C99''). HISTORY
The cbrt() function appeared in 4.3BSD. The sqrtl() function appeared in FreeBSD 8.0. The cbrtl() function appeared in FreeBSD 9.0. BSD
March 5, 2011 BSD