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 test