复制 if[-v variable];then echo"variable is set"elseecho"variable is not set"fi
if [ -z "$var" ]; then echo "var is unset"; else echo "var is set to '$var'"; fi This is because it doesn't distinguish between a variable that is unset and a variable that is set to the empty string. That is to say, ifvar='', then the above solution will incorrectly ou...
if [ -z ${var+x} ]; then echo "var is unset"; else echo "var is set to '$var'"; fi 参考:https://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash 6、换算秒为分钟、小时 代码语言:javascript 复制 #!/bin/bash a=60100 swap_seconds () { SEC=$1...
Method 1 – Setting variable value (if unset) Let’s get started with the following demonstration. Run the following command: $echo$country The command will return nothing as the value of thecountrywasn’t set in the first place. If the value of the variable is unset, using the following...
nameref attribute)andvalueofany existing variablewiththe same name at a surrounding scope.Ifthereisno existing variable, the local variableisinitially unset. The following options can be usedtorestrict outputtovariableswiththe specified attributeortogive variables attributes: ...
be quotedtoforce the quotedportiontobe matchedasa string. Bracket expressionsinregular expressions must be treated carefully, since normal quoting characters lose their meaningsbetweenbrackets. If thepatternisstoredina shell variable, quoting the variable expansion forces the entirepatterntobe matchedasa ...
[[ $variable ==|!= "string" ]] - Test if a given string conforms the specified glob/regex: [[ $variable ==|=~ pattern ]] - Test if a given variable is [eq]ual/[n]ot [e]qual/[g]reater [t]han/[l]ess [t]han/[g]reater than or [e]qual/[l]ess than or [e]qual to...
Example-1: Check the variable is set or unset using ‘-z’ option Create a bash file namedcheck_var1.shwith the following script. Here, the first `if`condition will return true and “Num variable is not set” will print. In the next statement, 20 is assigned to the variable,$Num. ...
Bash has a few conditional expressions, of which you can use one to check if a variable is empty or not. That is the-zoperator. Using the-zoperator followed by a variable will result in trueif the variable is empty. The condition will evaluate to false if the variable is not empty. ...
Why is printf better than echo? How to check if a variable is set in Bash? SettingIFSfor a single statement readarray(akamapfile) issue Tools Match command-line arguments to their help text Bash/Tcsh Comparison Table Collections of scripts ...