Bash Assignment

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Bitwise negation flips the bits in the binary representation of the numeric operand. The corresponding binary digits of both operands are multiplied to produce a result; for any given digit, the resulting digit is 1 if and only if the corresponding digit in both operands is also 1. A binary digit of the result is 1 if and only if the corresponding digits of the operands differ.

For instance, if the first binary digit of the first operand is 1, and the first digit of the second operand is 0, the first digit of the result is 1. Assign the value of the expression that follows the operator, to the variable that precedes it.

For instance, let arguments will undergo globbing, pathname expansion, and word splitting unless you enclose the individual arguments in double quotes.

In the majority of situations, it's preferable to use double parentheses to evaluate arithmetic expressions.

An entire array can be assigned by enclosing the array items in parenthesis: is a relatively new addition to bash, it was not part of the original array implementation.

The following example shows some simple array usage (note the "[index]=value" assignment to assign a specific index): returns each item as a separate word.-g create global variables when used in a shell function; otherwise ignored -l to convert NAMEs to lower case on assignment -n make NAME a reference to the variable named by its value -r to make NAMEs readonly -t to make NAMEs have the `trace' attribute -u to convert NAMEs to upper case on assignment -x to make NAMEs export Using ` ' instead of `-' turns off the given attribute.Variables with the integer attribute have arithmetic evaluation (see the `let' command) performed when the variable is assigned a value.When used in a function, `declare' makes NAMEs local, as with the `local' command. Exit Status: Returns success unless an invalid option is supplied or a variable assignment error occurs.# # declare an array and set key values # declare -a arr=(1) # arr[0]=1 arr[1]=$(( arr[0] 1 )) echo $ # 1 echo $ # 2 for i in do arr[i]=$(( arr[i-1] arr[i-2] )) done echo $ # 199 declare -p arr ## expect #declare -a arr=([0]="1" [1]="3" [2]="4" [3]="7" [4]="11" [5]="18" [6]="29" [7]="47" [8]="76" [9]="123" [10]="199") option adds the associative array attribute to the variable name provided to the declare command.One thing you learn later in bash is to use certain builtin commands. Here we cover how to use the builtin declare to modify the attributes of bash variables allowing you to create of arrays, list functions, integers, and much more.bash -c "help declare" declare: declare [-a Af Fgilnrtux] [-p] [name[=value] ...] Set variable values and attributes. If no NAMEs are given, display the attributes and values of all variables.(If this sounds a little convoluted, that's because it is.See below for examples.) let evaluates each argument, arg, as a math expression. All numbers are represented internally as fixed-width integers.foobar() rab() bar() foo() foo ( declare -A arr ; arr["key"]=value ; declare -p arr ; ) foo ( declare -A arr ; arr["key"]=value3 ; declare -p arr ; ) bar rab foobar ## expect #:no variable named arr #foo:declare -A arr=([key]="value2" ) #:no variable named arr #declare -A arr=([key]="value" ) #:no variable named arr #declare -A arr=([key]="value" ) #:declare -A arr=([key]="value" ) #foo:declare -A arr=([key]="value2" ) #:declare -A arr=([key]="value" ) #declare -A arr=([key]="value3" ) #:declare -A arr=([key]="value" ) #bar:declare -A arr=([key]="value" ) #:declare -A arr=([key]="value" ) #rab:declare -- arr #:declare -A arr=([key]="value" ) #foobar:bar:declare -A arr=([key]="value2" ) #:declare -A arr=([key]="value" ) #! Some options similar to declare, local, and typeset. For example, you may want to make it so a variable may not be reassigned a new value. Although it doesn't hurt to know what it is at least or in case you have to migrate to ksh for some reason. For most cases, you do not need declare to assign values to a variable./bin/bash ## test-declare-nameref ## version 0.0.1 - initial ################################################## test-declare-nameref() ################################################## if [ $ -eq 0 ] then true else exit 1 # wrong args fi ################################################## test-declare-nameref ################################################## ## generated by create-stub2v0.1.2 ## on Mon, 0900 ## see In addition, to declare, the following commands allow modification of bash variable attributes. This can be accomplished using the bash builtin command declare. However, there may be side effects of declaring variable attributes after assignment.

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