var=$HOME if [[ ! -v var ]]; then echo "Variable is not set" elif [[ -z "$var" ]]; then echo "Variable is set to the empty string" else echo "Variable has the value: $var" fi OUTPUT 1 2 3 Variable has the value: /root Use the if-else statement with the -n option...
我需要检查许多需要设置的环境变量,以便运行我的bash脚本。/test.sh var is unsetvar is set to '123' 如果我在If块中检查未设置的变量,检查就会起作用但是,在for循环中,if块仅在设置了变量时才打印,而不是在未设置变量时打 浏览12提问于2017-06-21得票数 3 回答已采纳 2回答 BASH检查变量中是否存在 、...
set -e有一个例外情况,就是不适用于管道命令。 所谓管道命令,就是多个子命令通过管道运算符(|)组合成为一个大的命令。Bash 会把最后一个子命令的返回值,作为整个命令的返回值。也就是说,只要最后一个子命令不失败,管道命令总是会执行成功,因此它后面命令依然会执行,set -e就失效了。 请看下面这个例子。 #!
set--"${POSITIONAL_ARGS[@]}"# 将数组里的参数设置为当前 shell 的位置参数 echo"FILE EXTENSION = ${EXTENSION}"echo"SEARCH PATH = ${SEARCHPATH}"echo"DEFAULT = ${DEFAULT}"echo"Number files in SEARCH PATH with EXTENSION:"$(ls-1"${SEARCHPATH}"/*."${EXTENSION}" | wc -l) if [[ -n ...
${var:+word} 如果变量var被定义,那么返回 word,但不改变var的值。 实例 #!/bin/bashecho${var:-"Variable is not set"} ---> Variable is not setecho"1 - Value of var is ${var}" ---> 1- Value of var isecho${var:="Variable is not set"} --->Variable is not set 同时var已经被...
if [[ $foo = "$bar" ]] 如果你确实要执行模式匹配,聪明的做法是取一个更加有意义的变量名(例如 $patt),或者加上注释说明。 35. if [[ $foo =~ 'some RE' ]] 同上,如果 =~号右侧的值加上引号,它会散失特殊的正则表达式含义,而变成一个普通的字符串。
[index] = value )# Incorrect index initializationecho$var[14]# Missing {} in array referencesecho"Argument 10 is$10"# Positional parameter misreferenceif$(myfunction);then..;fi# Wrapping commands in $()elseifothercondition;then..# Using 'else if'f;f() {echo"hello world; } # Using ...
0 Expands to the name of the shell or shell script. This is set at shell initialization. If bash is invoked with a file of commands, $0 is set to the name of that file. If bash is started with the -c option, then $0 is set to the first argument after the string to be executed...
if [[ ${arr[*]} == *sub_string* ]]; then printf '%s\n' "sub_string is in array." fi case模式 case "$var" in *sub_string*) # Do stuff ;; *sub_string2*) # Do more stuff ;; *) # Else ;; esac 讲解 知识点就一个,* 通配符匹配任意数量的字符(包括零个字符) 判断字符串...
set -o history date last=$(echo `history |tail -n2 |head -n1` | sed 's/[0-9]* //') echo "last command is [$last]" case "1" in "1") date last=$(echo `history |tail -n2 |head -n1` | sed 's/[0-9]* //') ...