# 双括号在 for 循环中的使用 for (( i = 0; i < 5; i++)); do echo "循环中${i}"; done # 如何判断空的变量? # 这里会出现一个误区 [ ${emptyvar} = "" ],这个等于 [ = "" ],所以会报错 # 而下面的2个方法都是可行的 emptyvar= if [ "${emptyvar}" = "" ]; then echo "...
function empty { local var="$1" # Return true if: # 1. var is a null string ("" as empty string) # 2. a non set variable is passed # 3. a declared variable or array but without a value is passed # 4. an empty array is passed if test -z"$var" then [[ $( echo"1" ...
[student@studentvm1 testdir]$ File="TestFile1" ; touch $File ; if [ -s $File ] ; then echo "$File exists and contains data." ; elif [ -e $File ] ; then echo "$File exists and is empty." ; else echo "$File does not exist." ; fi TestFile1 exists and is empty. [stude...
[student@studentvm1 testdir]$ File="TestFile1" ; rm $File ; if [ -s $File ] ; then echo "$File exists and contains data." ; else echo "$File does not exist or is empty." ; fi TestFile1 does not exist or is empty. 现在创建一个空文件用来测试: [student@studentvm1 testdir]...
可以使用参数扩展 $ var=$fornina b c d e f g>do> var="${var:+"$var"}$n"# $var被设置且非空时,则替换为"$var">done$ ./sa"$var":a b c d e f g: # 上面的方法是如下2个方法方法的简写 #1if[ -n"$var"]thenvar="$var $n"elsevar=$nfi#2[-n"$var"] && var="$var $...
Check to see if a variable is empty or not Create a new bash file, named, and enter the script below. The script above stores the first command-line argument in a variable and then tests the argument in the next statement. This script will print the first argument because it is not em...
在bash中使用的If [[-n variable ]]语法是什么 、 我正在修复一些我经常看到的旧bash脚本 if [[ -n $VARIABLE ]]; then 语法我试着用谷歌搜索了一下,但是找不到为什么用"-n“,下面是我所知道的 Comparisons: -eq equal to -ne not equal to -lt less than -le less than or equal to -gt greate...
if [ -z "$variable"]; then echo "The variable is empty." else echo "The variable is not empty." fi OUTPUT 1 2 3 The variable is empty. Now, assign any value as demonstrated below. Again, you can set any value: a string, integer, or float value. Use -z Option 1 2 3...
使用嵌套的for循环bash 是一种在Linux命令行中执行循环操作的方法。Bash是一种常用的Unix shell和命令语言,用于编写和执行脚本。 在bash中,可以使用嵌套的for循环来实现对多个变量或数据集合的迭代处理。以下是嵌套的for循环bash的一般语法形式: 代码语言:txt 复制 for var1 in list1 do for var2 in list2 do ...
if [[ -z "${MY_VAR}" ]]; then echo "Empty variable, do not use it" else echo "Varible is not empty, safe to use it." fi You can use the-ntest operator to test if a variable is not empty. To summarize: Let's see it in details with examples. ...