Understanding default parameters
Many times we may pass certain parameters from the command line; sometimes, we may not pass any parameters at all. We may need to have certain default values to be initialized to certain variables.
We will understand this concept by the following script.
Create a default_argument_1.sh script as follows:
#!/bin/bash
MY_PARAM=${1:-default}
echo $MY_PARAMExecute the script and check:
$ chmod +x default_argument_1.sh One $ ./default_argument_1.sh One One $ ./default_argument_1.sh default
Create another default_argument_2.sh script:
#!/bin/bash
variable1=$1
variable2=${2:-$variable1}
echo $variable1
echo $variable2Output:
We executed the script two times:
When we passed two arguments, then
variable1was$1andvariable2was$2.In second case, when we passed only one argument, then
$1was taken as a default argument for$2. Therefore,variable1was used as defaultvariable2. If we do not give a second parameter, then the first parameter is taken as a default second parameter...
