Differences between declare, typeset and local variable in Bash
BashShellVariablesScopeDeclareBash Problem Overview
When typing variables in Bash, what is the difference between declare and typeset? When used inside a function: what is the difference between declare and typeset and local?
The only difference I have come across is that typeset is portable to ksh scripts. Other than that, are there any reasons why one should be preferred over the other?
UPDATE: Added local to the question.
Bash Solutions
Solution 1 - Bash
- Difference between
typesetanddeclare:
The former is more portable(e.g. ksh), while the latter is more preferable when portability is not a concern.
- Difference between
declare(ortypeset) andlocalwhen used inside a function:
The former implies the latter, but more powerful. For example, declare -i x makes x have the integer attribute, declare -r x makes x readonly, etc.
Solution 2 - Bash
As far as bash is concerned, no, there is no difference. In fact, the manpage has them share the same definition
> declare [-aAfFilrtux] [-p]
> [name[=value] ...]
typeset
> [-aAfFilrtux] [-p] [name[=value]
> ...]
Declare variables and/or
> give them attributes. If no names are
> given then display the values of
> variables. The -p option will display
> the attributes and values of each
> name...
I also found this little tidbit which further substantiates my claim as well as the ksh portability you mentioned.
> The declare or typeset builtins, > which are exact synonyms, permit modifying the properties of variables. > This is a very weak form of the typing > [1] available in certain programming > languages. The declare command is > specific to version 2 or later of > Bash. The typeset command also works > in ksh scripts.
Solution 3 - Bash
In the Bash manual under section 4.2 Bash Builtin Commands it states:
>'typeset'
typeset [-afFrxi] [-p] [NAME[=VALUE] ...]
The 'typeset' command is supplied for compatibility with the Korn
shell; however, it has been deprecated in favor of the 'declare'
builtin command.