KSH variable

最新推荐文章于 2021-05-14 18:05:38 发布

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最新推荐文章于 2021-05-14 18:05:38 发布

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分类专栏： Unix Shell 文章标签： unix shell ksh

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本文详细介绍了KornShell(KSH)中的三种主要变量类型：函数变量、脚本/文件变量和系统环境变量，并探讨了它们的作用域、继承及共享方式。此外，还深入讲解了变量的设置、删除、数值型变量的声明及其属性设置方法。

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KSH Variable Category

function variable
1. It must be explicitly declared within a function using typeset command.
2. It's valid only within the function it is declared.
script/file variable
1. It's defined in a file, and valid in that file.
2. script/file variable is not valid in its callee script/file, until it's EXPORT-ed to environment.
system environment variable
1. environment can be shared anywhere.

All function variables, except those explicitly declared locally within the function with the typeset command, are inherited and shared by the calling Korn shell script.

For example:

# Function variable:
# Functions act almost just like external scripts, all variables are SHARED between the same ksh process.
# If a variable is changed inside a function, the variable value is changed after it has left the function.

VARA=AA
VARB=BB

function foo
{
  echo "1: VARA=$VARA,VARB=$VARB,VARC=$VARC"    # 1: VARA=AA,VARB=BB,VARC=
  eval $1=AF    # action VARA=AF
  VARB=BF
  VARC=CF
}

foo VARA

echo "2: VARA=$VARA,VARB=$VARB,VARC=$VARC"      # 2: VARA=AF,VARB=BF,VARC=CF

Variable Type

Basically, there is no data type concept inksh (except typeset -i, we will talk later), all values can be treated asstring; and when a numeric value is required , it can be converted dynamicallyas needed.

Variable Set

VAR_NAME1="ABC"

VAR_NAME2=ABC                        #same as “ABC”

VAR_NAME3="123"

VAR_NAME4=20                         # same as “20”, but it can be parsed asnumeric when needed.


VAR_ID1=NAME5

VAR_ID2=NAME6


eval VAR_${VAR_ID1}=true               # VAR_NAME5=true, it’s same as “true”

eval VAR_${VAR_ID2}=false              # VAR_NAME6=false, it’s same as “false”


VAR_NAME7=${VAR_NAME3}                    # VAR_NAME7=”123”

eval VAR_NAME8=\$\{VAR_${VAR_ID1}\}       # VAR_NAME8=true, the value of VAR_NAME5

Variable Unset

unset VAR_NAME7                    # unsetVAR_NAME7

unset VAR_${VAR_ID1}             # unset VAR_NAME5

Numeric Variable

let’s talk about “-i” attribute, which isused to declare a variable as numeric type.

typeset -i VAR_INT=12

typeset -i VAR_INT=”12”          # has same behavior as “12”, because string“12” was parsed as integer 12.


When a variable is declared as an integer,it can be calculated as:

VAR_INT=VAR_INT+5

Instead of

((VAR_INT=VAR_INT+5))