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 [