I use the following script to see if the file exists:

#!/bin/bash

FILE=$1     
if [ -f $FILE ]; then
   echo "File $FILE exists."
else
   echo "File $FILE does not exist."
fi

If I just want to check that the file does not exist, what is the correct syntax to use?

#!/bin/bash

FILE=$1     
if [ $FILE does not exist ]; then
   echo "File $FILE does not exist."
fi

#1st floor

test thing may also count.It's for me useful (based on Bash Shell: Check that the file exists ):

test -e FILENAME && echo "File exists" || echo "File doesn't exist"

#2nd floor

To undo the test, use'!'.This is equivalent to the "not" logical operator in other languages.Try this:

if [ ! -f /tmp/foo.txt ];
then
    echo "File not found!"
fi

Or in a slightly different way:

if [ ! -f /tmp/foo.txt ]
    then echo "File not found!"
fi

Or you can use:

if ! [ -f /tmp/foo.txt ]
    then echo "File not found!"
fi

Or, keep it all the same:

if ! [ -f /tmp/foo.txt ]; then echo "File not found!"; fi

This can be written (using the "and" operator: &&):

[ ! -f /tmp/foo.txt ] && echo "File not found!"

Looks shorter:

[ -f /tmp/foo.txt ] || echo "File not found!"

#3rd floor

This Shell script can also be used to find files in the directory:

echo "enter file"

read -r a

if [ -s /home/trainee02/"$a" ]
then
    echo "yes. file is there."
else
    echo "sorry. file is not there."
fi

#4th floor

To test the existence of a file, the parameter can be any of the following:

-e: Returns true if file exists (regular file, directory, or symlink)
-f: Returns true if file exists and is a regular file
-d: Returns true if file exists and is a directory
-h: Returns true if file exists and is a symlink

All of the following tests apply to regular files, directories, and symbolic links:

-r: Returns true if file exists and is readable
-w: Returns true if file exists and is writable
-x: Returns true if file exists and is executable
-s: Returns true if file exists and has a size > 0

Sample script:

#!/bin/bash
FILE=$1

if [ -f "$FILE" ]; then
   echo "File $FILE exists"
else
   echo "File $FILE does not exist"
fi

#5th floor

Bash File Test

-b filename - block special files
-c filename special character file
-d directoryname - Check if the directory exists
-e filename Checks whether a file exists, regardless of type (node, directory, socket, etc.)
-f filename checks if a regular file exists instead of a directory
-G filename - Check that the file exists and is owned by a valid group ID
-G filename set-group-id-true if the file exists and is set-group-id
-k filename - viscous bit
-L filename - Symbolic link
-O filename True if the file exists and is owned by a valid user ID
-r filename - Check if the file is readable
-S filename - Check if the file is a socket
-s filename checks if the file is non-zero size
-u filename checks if the file set-user-id bit is set
-w filename Check if the file is writable
-x filename Check whether the file is executable

How to use:

#!/bin/bash
file=./file
if [ -e "$file" ]; then
    echo "File exists"
else 
    echo "File does not exist"
fi 

You can use! To negate the test expression! Operator

#!/bin/bash
file=./file
if [ ! -e "$file" ]; then
    echo "File does not exist"
else 
    echo "File exists"
fi