54 lines
921 B
Markdown
54 lines
921 B
Markdown
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# conditions.
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## boolean check.
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```bash
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local predicate=true # or false.
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if $predicate; then
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# if true.
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else
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# if false.
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fi
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```
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## variables comparison.
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```bash
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local var1="test"
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local var2="test"
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if [[ "$var1" = "$var2" || "$var1" != "$var2" ]]; then
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# if equal or not equal.
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fi
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if [[ "$var1" =~ "[Tt]est" ]]; then
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# if matches regex.
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fi
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if [[ "$var1" > "$var2" || "$var1" < "$var2" ]]; then
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# string comparison (lexographical).
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fi
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if [[ -z "$var1" || "$var1" = "" ]]; then
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# if variable is empty
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fi
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if [[ -n "$var1" || "$var1" != "" ]]; then
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# if variable not empty.
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fi
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```
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please note that spaces inside `[[ ... ]]` are required (because \[ and \] are actually operators).
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## negation.
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add ! before condition. space before and after required.
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```bash
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local var1=true
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if ! $var1; then ...
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if [[ ! -f test.txt ]]; then ...
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```
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## check if file exists.
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```bash
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if [[ -f file.txt ]]; then ...
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```
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