SHELL

bash function arguments

#!/usr/bin/env sh

foo 1  # this will fail because foo has not been declared yet.

foo() {
    echo "Parameter #1 is $1"
}

foo 2 # this will work.

bash function arguments

#!/bin/bash
#!/bin/bash
# Name - math.sh
# Purpose - Demo return value 
# ------------------------------------

## user define function
math(){
	local a=$1
	local b=$2
	local sum=$(( a + b))
	return $sum
}

## call the math function with 5 and 10 as  arguments 
math 5 10

## display back result (returned value) using $?
echo "5 + 10 = $?"

bash function arguments

Function shell variables
All function parameters or arguments can be accessed via $1, $2, $3,..., $N.
$0 always point to the shell script name.
$* or $@ holds all parameters or arguments passed to the function.
$# holds the number of positional parameters passed to the function.
How do I display function name?
$0 always point to the shell script name. However, you can use an array variable called FUNCNAME which contains the names of all shell functions currently in the execution call stack. The element with index 0 is the name any currently-executing shell function.This variable exists only when a shell function is executing.

FUNCNAME in action
Create a shell script called funcback.sh:




#!/bin/bash
#  funcback.sh : Use $FUNCNAME
backup(){
	local d="$1"
	[[ -z $d ]] && { echo "${FUNCNAME}(): directory name not specified"; exit 1; }
	echo "Starting backup..."
}

backup $1

bash function arguments

#!/bin/bash
# Name - cmdargs.sh
# Purpose - Passing positional parameters to user defined function 
# -----------------------------------------------------------------
file="$1"

# User-defined function
is_file_dir(){
        # $f is local variable
	local f="$1"
        # file attributes comparisons using test i.e. [ ... ]
	[ -f "$f" ] && { echo "$f is a regular file."; exit 0; }
	[ -d "$f" ] && { echo "$f is a directory."; exit 0; }
	[ -L "$f" ] && { echo "$f is a symbolic link."; exit 0; }
	[ -x "$f" ] && { echo "$f is an executeble file."; exit 0; }
}

# make sure filename supplied as command line arg else die
[ $# -eq 0 ] && { echo "Usage: $0 filename"; exit 1; }

# invoke the is_file_dir and pass $file as arg
is_file_dir "$file"

bash function parameter

#!/bin/bash

my_func() {
    echo "$1 $2 $3"
}

my_func "hello" "grepper" "friends"

bash function arguments

#!/bin/bash
# Name: bash-task.sh
# Purpose: Check if a file exists or not using custom bash function and return value
# -----------------------------------------------------------------------------------

# set values 
readonly TRUE=0
readonly FALSE=1

# get input from the CLI
file="$1"

# return $TRUE (0) if file found 
# return $FALSE (1) if file not found
is_file_found(){
	[ -f "$1" ] && return $TRUE || return $FALSE
}

# show usage info if $1 not passed to our script
if [ $# -eq 0 ]
then
	echo "Usage: $0 filename"
	exit 1
fi

# let us call our function 
is_file_found "$file"

# take action based upon return value
if [ $? -eq 0 ]
then
	echo "$file added to backup task"
else
	echo "$file not found."
fi

bash function arguments

#!/bin/bash
 
# write a function
fresh(){
   # t stores $1 argument passed to fresh()
   t=$1
   echo "fresh(): $0 is $0"
   echo "fresh(): $1 is $1"
   echo "fresh(): $t is $t"
   echo "fresh(): total args passed to me $#"
   echo "fresh(): all args ($@) passed to me -"$@""
   echo "fresh(): all args ($*) passed to me -"$*""
}
 
# invoke the function with "Tomato" argument
echo "**** calling fresh() 1st time ****"
fresh Tomato
 
# invoke the function with total 3 arguments
echo "**** calling fresh() 2nd time ****"
fresh Tomato Onion Paneer

bash function arguments

function_name(){
   command_block_here
}
## OR ##
function function_name_here(){
   command_line_block
}
## passing parameters to a Bash function ##
my_function_name(){
  arg1=$1
  arg2=$2
  command on $arg1
}