在Bash Shell中,可以使用复合条件来在一个if语句中检查多个条件。复合条件主要有两种形式:逻辑与(&&)和逻辑或(||)。 1. 逻辑与(&&): - 概念:逻辑与用于同时检查多个条件...
How to check if a variable exists or is “null”? How to check if a file exists? How to check if a directory exists? How to check if a command succeeds or failed? How to do string comparison and check if a string equals to a value? How to check if a string is in an array?
- Test if the specified variable has a [n]on-empty value: [[ -n $variable ]] - Test if the specified variable has an empty value: [[ -z $variable ]] - Test if the specified [f]ile exists: [[ -f path/to/file ]] - Test if the specified [d]irectory exists: [[ -d path/...
echo "check if variable with name $1 exists"} assert_var "FOO"我们的期望是,应该检测变量FOO,同时也不存在BAR。为此,我需 浏览0提问于2020-07-01得票数 0 回答已采纳 2回答 以未实例化的变量为条件 我是Bash脚本的新手,对C-type语言有更多的经验。我已经编写了一些带有条件的脚本,用于检查未实例化...
/bin/bash # declare STRING variable STRING="Hello World" #print variable on a screen echo $STRING Navigate to a directory where your hello_world.sh is located and make the file executable: $ chmod +x hello_world.sh Now you are ready to execute your first bash script:...
- Testifthe specified variable has an empty value: [[ -z$variable]] - Testifthe specified [f]ile exists: [[ -f path/to/file ]] - Testifthe specified [d]irectory exists: [[ -d path/to/directory ]] - Testifthe specified file or directory [e]xists: ...
" ## Check whether a filename was entered if [ -n "$filename" ] then if [ $verbose -gt 0 ] then printf "Filename is %s\n" "$filename" fi else if [ $verbose -gt 0 ] then printf "No filename entered\n" >&2 fi exit 1 fi ## Check whether file exists if [ -f "$...
Checking if a variable exists ([[ -v varname ]]): Yes, this is possibly a killer argument, but consider the programming style of always setting variables, so you don't need to check if they exist.Are empty string comparisons any special?Of...
-z foo - Check if variable exists String Operators = - Equals == - Equals -z - Is null -n - Is not null < - Is less than in ASCII alphabetical order > - Is greater than in ASCII alphabetical order If Statements #!/bin/bash [[ if [[$foo = 'bar']]; then echo 'one' elif...
As you can see the filemath.shexists! Most of the time when you’re writing bash scripts you won’t be comparing two raw values or trying to find something out about one raw value, instead you’ll want to create a logical statement about a value contained in a variable. Variables behav...