checking whether a command is executed or not within if in bash

I am new in bash programming , was try to execute a program which will create a directory on basis of complete path provided to it from prompt and if directory already exists it will return error for directory already exists and ask again for name in recursive function. here it is what I did

let say a file test1 in it

#!/bin/bash
echo "enter the directory name"
read ab
check(){
if (( echo `mkdir $ab` 2>/dev/null )); then
  echo "directory created "
  echo `ls -ld $ab`
  exit
else
  echo "try again "
  echo "enter new value for directory:
  read ab
  check
fi
}
check

the problem here is if the directory exists then the program works fine but if does not exist then it creates it but then goes to the else part of the program . please help

Solution

You can use a test to see if the directory exists. If you want to repeatedly ask for a directory name until you get one, use a loop:

while true
do
    read -p"Directory Name: " directory
    if [[ -d $directory ]]     # Directory already exists
    then
        echo "Directory '$directory' already exists. Try again."
        continue
    fi
    mkdir "$directory" && break

    echo "Cannot create directory $directory"
    exit 2             # Or whatever
done

A while true loop is an infinite loop. However, I have two loop controls in the loop: A continue statement that goes back to the top of the loop, and a break statement that ends the loop. It's why that infinite loop (like all infinite loops) isn't really infinite.

I use [[ -d "$directory" ]] to test to see if the directory already exists or not. If it already does exist, I'll echo something to that effect, and use continue to go back and re-prompt for the directory name.

Note that my read uses a -p parameter. This is my prompt used for the read command. It's a nice easy way to combine the read with the prompt.

mkdir "$directory" && break means to make the directory. The && is a list operator. It says to run the command on the left (the mkdir) and if it is successful (i.e. it returns a zero exit status), then run the command on the right (the break) and exit my loop. It's equivalent to:

If mkdir "$directory"
then
    break
fi

The other list operator is ||. It says if the command on the left failed (that it returned a non-zero exit status), then run the command on the right.

For example:

[[ -d $directory ]] || mkdir "$directory"

is equivalent to:

if [[ ! -d $directory ]]
then
    mkdir "$directory"
fi

I through in a lot of things in here on purpose to demonstrate a lot of standard things you'll see in various shell scripts.

Use [[ ... ]] for testing. There are lots of various tests for files, directories, strings, and boolean tests. Learn them.
Use -p for read prompts.
Get use to the various list operators, you'll see them a lot.
Understand how you can control loops via continue and break. It's not unusual to use loops like this to make sure the correct parameter is entered.