Bash quick cheatsheat (‘if’ checks and other useful commands)

Creating this post to dump here various bash shell and script commands, tips and tricks which I found useful in my everyday work. Will update it with new info continually…
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Check in bash if a file exists or not and do something in each case:

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

———
Check only if a file DOES NOT exist:

if [ ! -f $FILE ]; then
  echo "File not found!"
fi

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In the above examples FILE can be set to any file name or any of the command line arguments (you need to add these lines BEFORE the ‘if’ statements):

FILE=/tmp/foo.txt  # set file to some knowon file name
FILE=$3            # set file to argument 3 from the bash command line