How to Set / Unset Default Value for Command Line Arguments For a shell script?

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While doing shell scripting you will use command line arguments to pass the values to the program. The program has to verify the value of the command line arguments whether it is having proper values assigned before further execution. Otherwise you can assign a default value for the parameter or argument if applicable.

Syntax:

variable1=${1:-value for the variable} # 1 represent the $1(second argument for the command line

Or

variable1=${1-value for the variable}

To Unset the parameter value

unset  variable1

$ cat tst.sh

echo "Test Program"

log_d=/u01/log

dat_d=/u01/dat

Log_Dir=${1:-$log_d}

echo "Log Directory:" $Log_Dir

Dat_Dir=${2:-$dat_d}

echo "Data Directory:" $Dat_Dir

Output

Without passing the command line value

tst.sh

Test Program

Log Directory: /u01/log

Data Directory: /u01/dat

Passing the command line value

$ tst.sh /u07/log /u07/dat

Test Program

Log Directory: /u07/log

Data Directory: /u07/dat

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