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Arguments and Parameters

Command Line Arguments

# Try the following commands

#This is terminal not a script

$ ls unknown_directory

No such file or directory.

#The first word on command line is, ls - is name of the command to #+be executed.


#Everything else on command line is taken as arguments to this #+command. For e.g.

$ tail -3 myf

#Name of command is tail, and the arguments are -3 and myf.

 

NOTE: Variable $# holds number of arguments specified on command line and $* or $@ refer to all arguments passed to script.

Exercise:Try to determine command and arguments from following commands

$ cd ..

$ ls –lar foo

$ mv –v bot1.txt bot2.txt

$ date

$ clear

Command No. of argument to this command (i.e $#) Actual Argument
cd 1 ..
Ls 4 foo& -l, -a ,-r
Cp 2 y and y.bak
mv 3 -v , & bot1.txt bot2.txt
date 0  
clear 0  

 

Command Line arguments in Scripting

#!/bin/bash

#arguments.sh

#Script illustrating use of positional parameters

echo “The name of the program is $0”

echo “The first argument is $1”

echo ”The second argument is $2”

echo “The number of arguments are $#”

echo “They are $*”

exit 0
TERMINAL àEXECUTION OF SCRIPT

$ bash arguments.sh test1 test2

The name of the program is arguments.sh

The first argument is test1

The second argument is test2

The number of arguments are 2

They are

test1 test2

 

Example:

#!/bin/bash

#arguments1.sh

#Practical example

# Read a file but give the name of file externally using parameter

#The file should be in the directory of shellscript arguments1.sh

#Script illustrating use of positional parameters

echo “The name of the program is $0”

echo “The first argument is $1”

cat $1

exit 0
TERMINAL àEXECUTION OF SCRIPT

$ bash arguments1.sh [file_name]

The name of the program is arguments1.sh

The first argument is [file_name]