file/folder existence

General syntax in BASH shell is:

[ parameter FILE ]
OR
test parameter FILE

Where parameter can be any one of the following:

• -e: Returns true value if file exists
• -f: Return true value if file exists and regular file
• -r: Return true value if file exists and is readable
• -w: Return true value if file exists and is writable
• -x: Return true value if file exists and is executable
• -d: Return true value if exists and is a directory

For example,

Find out if file /etc/passwd file exists or not:
$ [ -f /etc/passwd ] && echo "File exists" || echo "File does not exists"

# Make the directory for the job ID you are running if it does not exist
[ -d $HOME/scratch/jobid_$JOB_ID ] || mkdir -p $HOME/scratch/jobid_$JOB_ID

You can use conditional expressions in a shell script:

#!/bin/bash
FILE=$1

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

See if a directory exists or not with NOT operator:
[ ! -d directory ]
OR
! test directory