$ curl cheat.sh/

# if
# Performs conditional processing in shell scripts.
# See also: `test`, `[`.
# More information: <https://www.gnu.org/software/bash/manual/bash.html#Conditional-Constructs>.

# Execute the specified commands if the condition command's exit status is zero:
if condition_command; then echo "Condition is true"; fi

# Execute the specified commands if the condition command's exit status is not zero:
if ! condition_command; then echo "Condition is true"; fi

# Execute the first specified commands if the condition command's exit status is zero otherwise execute the second specified commands:
if condition_command; then echo "Condition is true"; else echo "Condition is false"; fi

# Check whether a [f]ile exists:
if [[ -f path/to/file ]]; then echo "Condition is true"; fi

# Check whether a [d]irectory exists:
if [[ -d path/to/directory ]]; then echo "Condition is true"; fi

# Check whether a file or directory [e]xists:
if [[ -e path/to/file_or_directory ]]; then echo "Condition is true"; fi

# Check whether a variable is defined:
if [[ -n "$variable" ]]; then echo "Condition is true"; fi

# List all possible conditions (`test` is an alias to `[`; both are commonly used with `if`):
man [

$

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