In this post, we will learn how to use inbuild special symbols in the shell to make our code simple.
Let’s assume we have a file in the temp directory and we will use the inbuilt keyword to test the functionality.

We have 2 files in the Desktop

The ls command shows all the files in the current directory.

root@vps43086554:~/Desktop# ls
sample.sh sample.txt
root@vps43086554:~/Desktop#

Now will make a simple shell script sample.sh where we will write an if condition where the condition will check with the help of existing keywords.

if [ -e sample.txt ];
then echo “Inside if ture part”
fi

In the above the if condition we have written an if the condition where we have written -e and a file name.

File Operators

-e

Ture if file exists.
Menas it will check if the file exists in the directory then it will return true.

Prerequisite -Create 2 files sample.sh sample.txt

if [ -e sample.txt ];
then echo “Inside if ture part”
fi

Output-
root@vps43086554:~/Desktop# sh sample.sh
Inside if ture part
root@vps43086554:~/Desktop#

-d

True if the file is a directory.

Prerequisite- Create a folder named a folder.

Code to create a folder named as folder.

root@vps43086554:~/Desktop# mkdir folder
root@vps43086554:~/Desktop# ls
folder sample.sh sample.txt

Code to check the folder is exists or not.

if [ -e folder ];
then echo “Inside if ture part”
fi

Output

root@vps43086554:~/Desktop# sh sample.sh
Inside if ture part

-f

True if the file exists and the file is a regular file.

Prerequisite- Create an invalid file named non_normarl.gfd.

Code-

if [ -f non_normal.gfd ];
then echo “Inside if ture part”
fi
if [ -f sample.txt ];
then echo “Inside if ture part of valid file”
fi

root@vps43086554:~/Desktop# sh sample.sh
Inside if ture part of valid file

-r

True if the file is readable by you

-s

True if the file exists and is not empty.

-w

True if the file is writable by you.

-x

True if the file is executable by you.

String Operators

-z “String”

True if the string is empty

-n “String”

True if the file is not empty.

STRING1=STRING2

True id the strings are equal.

STRING1!=STRING2

True if the strings are not equal.

agr1 -eq arg2

True if arg1 is equal to arg2

agr1 -nq arg2

True if arg1 is not equal to arg2

arg1 -lt arg2

True if the arg1 is less than arg2

arg1 -le arg2

True if arg1 is less than or equal to arg2

arg1 -gt arg2

True if the arg1 is greater than arg2

arg1 -ge arg2

True if the arg1 is greater than or equal to arg2