is_defined
Function description
The is_defined function may be used to test whether a named variable has been defined, even if it currently holds a null value.
Function parameters
$1 - The name of the variable to test.
Return value
The is_defined function will return zero if the named variable is defined (even if it contains a null value) or non-zero if the named variable is undefined.
Example use
Listing 1
- #! /bin/bash
- # We rely on some functions from hacking-bash.sh
- [[ -r ${HACKING_BASH_LIB_PATH:=/usr/lib/hacking-bash.sh} ]] && \
- source ${HACKING_BASH_LIB_PATH} || \
- { echo "Unable to find ${HACKING_BASH_LIB_PATH}"; exit 1; }
- # Create some variables
- DEFINED_BUT_EMPTY=""
- DEFINED_AND_SET="hello!"
- unset UNDECLARED_VAR
- # Test them
- is_defined DEFINED_BUT_EMPTY && echo "DEFINED_BUT_EMPTY is defined"
- is_defined DEFINED_AND_SET && echo "DEFINED_AND_SET is defined"
- is_defined UNDECLARED_VAR && echo "UNDECLARED_VAR is defined"
Example code demonstrating the is_defined function
max@lisa ~ $ ./is_defined.sh
DEFINED_BUT_EMPTY is defined
DEFINED_AND_SET is defined