All About Variables

Format

VARIABLE_NAME = value

echo $VARIABLE_NAME  

Types

• scalar variable -- holds 1 value at a time (aka name value pairs)
• array variable -- holds 0 or more values

Variable Names

• a-z, 0-9 or underscore
• conventionally uppercase
• start with letter

Setting Values

PET=fish

PET='fish bowl'

PET="fish bowl"

Setting Scalar Values

->PET= cat #A space will cause an error

ksh: cat:  not found

->PET=cat

->echo $PET

cat

->pet='cat fish'

->echo $pet

cat fish

->PET=ferret

->echo $pet   # $pet is not the same as $PET

cat fish  

->echo $PET

ferret

Setting Array Values

->PET[1]=FERRET

->PET[2]=parrot

->echo ${PET[1]}

FERRET

->echo ${PET[2]}

parrot

->echo ${PET[0]}# set since name is same as scalar variable

ferret

Set Variables to Read-only

->readonly PET # now PET can't be set to a value

->PET=dog

ksh: PET: is read only

Unset Variables (if not readonly)

->TREE=oak

->echo $TREE

oak

->unset TREE

->echo $TREE

Variable Types

  local

available within the current instance. not available to programs started by the shell

  environment

variable available to child processes Use export to create an environmental variable from a local variable                         export VARIABLE=value

  shell

special variables set by the shell