# [
# Check file types and compare values.
# Returns 0 if the condition evaluates to true, 1 if it evaluates to false.
# More information: <https://www.gnu.org/software/bash/manual/bash.html#index-test>.
# Test if a given variable is equal/not equal to the specified string:
[ "$variable" ==|!= "string" ]
# Test if a given variable is [eq]ual/[n]ot [e]qual/[g]reater [t]han/[l]ess [t]han/[g]reater than or [e]qual/[l]ess than or [e]qual to the specified number:
[ "$variable" -eq|ne|gt|lt|ge|le integer ]
# Test if the specified variable has a [n]on-empty value:
[ -n "$variable" ]
# Test if the specified variable has an empty value:
[ -z "$variable" ]
# Test if the specified [f]ile exists:
[ -f path/to/file ]
# Test if the specified [d]irectory exists:
[ -d path/to/directory ]
# Test if the specified file or directory [e]xists:
[ -e path/to/file_or_directory ]
$
cheat.sh
tldr