How do I test existence of a text file in bash running under Unix like operating systems?

You need to use the test command to check file types and compare values. The same command can be used to see if a file exist of not. The syntax is as follows:

test -e filename
[ -e filename ]

test -f filename
[ -f filename ]

The following command will tell if a text file called /etc/hosts exists or not usingbash conditional execution:

[ -f /etc/hosts ] && echo "Found" || echo "Not found"

Sample outputs:

Found

The same code can be converted to use withif..else..fiwhich allows to make choice based on the success or failure of a test command:

#!/bin/bash
file="/etc/hosts"
if [ -f "$file" ]
then
	echo "$file found."
else
	echo "$file not found."
fi

File test operators

The following operators returns true if file exists:

-b FILE
              FILE exists and is block special

       -c FILE
              FILE exists and is character special

       -d FILE
              FILE exists and is a directory

       -e FILE
              FILE exists

       -f FILE
              FILE exists and is a regular file

       -g FILE
              FILE exists and is set-group-ID

       -G FILE
              FILE exists and is owned by the effective group ID

       -h FILE
              FILE exists and is a symbolic link (same as -L)

       -k FILE
              FILE exists and has its sticky bit set

       -L FILE
              FILE exists and is a symbolic link (same as -h)

       -O FILE
              FILE exists and is owned by the effective user ID

       -p FILE
              FILE exists and is a named pipe

       -r FILE
              FILE exists and read permission is granted

       -s FILE
              FILE exists and has a size greater than zero

       -S FILE
              FILE exists and is a socket

       -t FD  file descriptor FD is opened on a terminal

       -u FILE
              FILE exists and its set-user-ID bit is set

       -w FILE
              FILE exists and write permission is granted

       -x FILE
              FILE exists and execute (or search) permission is granted

(Fig.01: File test operators taken from bash man page)

The syntax is same (seeFile operators (attributes) comparisonsfor more info):

if [ operator FileName ]
then
     echo "FileName - Found, take some action here"
else
   echo "FileName - Not found, take some action here"
fi