tldr/pages/common/if.md

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# if
> Simple shell conditional.
> See also: `test`, `[`.
- Execute two different commands based on a condition:
`if {{command}}; then {{echo "true"}}; else {{echo "false"}}; fi`
- Check if a variable is defined:
`if [[ -n "{{$VARIABLE}}" ]]; then {{echo "defined"}}; else {{echo "not defined"}}; fi`
- Check if a file exists:
`if [[ -f "{{path/to/file}}" ]]; then {{echo "true"}}; else {{echo "false"}}; fi`
- Check if a directory exists:
`if [[ -d "{{path/to/directory}}" ]]; then {{echo "true"}}; else {{echo "false"}}; fi`
- Check if a file or directory exists:
`if [[ -e "{{path/to/file_or_directory}}" ]]; then {{echo "true"}}; else {{echo "false"}}; fi`
- List all possible conditions (`test` is an alias to `[`; both are commonly used with `if`):
`man [`