mirror of https://github.com/CrimsonTome/tldr.git
if: update page (#7481)
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# if
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> Simple shell conditional.
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> Performs conditional processing in shell scripts.
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> See also: `test`, `[`.
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> More information: <https://www.tcl.tk/man/tcl8.6.11/TclCmd/if.html>.
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> More information: <https://www.gnu.org/software/bash/manual/bash.html#Conditional-Constructs>.
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- Execute two different commands based on a condition:
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- Execute the specified commands if the condition command's exit status is zero:
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`if {{command}}; then {{echo "true"}}; else {{echo "false"}}; fi`
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`if {{condition_command}}; then {{echo "Condition is true"}}; fi`
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- Check if a variable is defined:
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- Execute the specified commands if the condition command's exit status is not zero:
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`if [[ -n "{{$VARIABLE}}" ]]; then {{echo "defined"}}; else {{echo "not defined"}}; fi`
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`if ! {{condition_command}}; then {{echo "Condition is true"}}; fi`
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- Check if a file exists:
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- Execute the first specified commands if the condition command's exit status is zero otherwise execute the second specified commands:
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`if [[ -f "{{path/to/file}}" ]]; then {{echo "true"}}; else {{echo "false"}}; fi`
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`if {{condition_command}}; then {{echo "Condition is true"}}; else {{echo "Condition is false"}}; fi`
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- Check if a directory exists:
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- Check whether a [f]ile exists:
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`if [[ -d "{{path/to/directory}}" ]]; then {{echo "true"}}; else {{echo "false"}}; fi`
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`if [[ -f {{path/to/file}} ]]; then {{echo "Condition is true"}}; fi`
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- Check if a file or directory exists:
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- Check whether a [d]irectory exists:
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`if [[ -e "{{path/to/file_or_directory}}" ]]; then {{echo "true"}}; else {{echo "false"}}; fi`
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`if [[ -d {{path/to/directory}} ]]; then {{echo "Condition is true"}}; fi`
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- Check whether a file or directory [e]xists:
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`if [[ -e {{path/to/file_or_directory}} ]]; then {{echo "Condition is true"}}; fi`
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- Check whether a variable is defined:
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`if [[ -n "${{variable}}" ]]; then {{echo "Condition is true"}}; fi`
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- List all possible conditions (`test` is an alias to `[`; both are commonly used with `if`):
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