Bash Scripting with Parameters Accessing Parameters
Example
When executing a Bash script, parameters passed into the script are named in accordance to their position: $1 is the name of the first parameter, $2 is the name of the second parameter, and so on.
A missing parameter simply evaluates to an empty string. Checking for the existence of a parameter can be done as follows:
if [ -z "$1" ]; then
echo "No argument supplied"
fi
Getting all the parameters
$@ and $* are ways of interacting with all the script parameters. Referencing the Bash man page, we see that:
$*: Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, it expands to a single word with the value of each parameter separated by the first character of the IFS special variable.$@: Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, each parameter expands to a separate word.
Getting the number of parameters
$# gets the number of parameters passed into a script. A typical use case would be to check if the appropriate number of arguments are passed:
if [ $# -eq 0 ]; then
echo "No arguments supplied"
fi
Example 1
Loop through all arguments and check if they are files:
for item in "$@"
do
if [[ -f $item ]]; then
echo "$item is a file"
fi
done
Example 2
Loop through all arguments and check if they are files:
for (( i = 1; i <= $#; ++ i ))
do
item=${@:$i:1}
if [[ -f $item ]]; then
echo "$item is a file"
fi
done
