$ ls -l | > while read perms links owner group size month day time file > do > printf "%10d %s\n" "$size" "$file" > totalsize=$(( ${totalsize:=0} + ${size:-0} )) > done $ echo ${totalsize-unset} ## print "unset" if variable is not set unset 通过使用进程替换,变量t...
if 先来个实例: x=5; if [ $x = 5 ]; then echo 'x equals 5...中的条件语句, Test 是核心,if 和 case 熟悉语法即可。...循环 bash 中有 for 和 while 两种常见的循环体,我们应该都很熟悉。 for 直接上实例,批量修改文件名。...; done 语法其实很明朗: for variable [in words]; do comman...
You can assign data to a variable using the equals sign (=). The data you store in a variable can either be a string or a number. Let’s create a variable now on the command line: chapter_number=5 The variable name is on the left hand side of the equals sign, and the data whic...
上面语法中,for循环会依次从list列表中取出一项,作为变量variable,然后在循环体中进行处理。关键词do可以跟for写在同一行,两者使用分号分隔。for variable in list; do commands done下面是一个例子。#!/bin/bash for i in word1 word2 word3; do echo $i done上面例子中,word1 word2 word3是一个包含三个...
We’ll be checking whether 1 equals 2. If true, then the output will be “true”. Otherwise, the output will be “false”. $ test 1 -eq 2 && echo“true” || echo“false” Let’s break it down. test: The test command. 1: The first element for comparison. -eq: Comparison ...
x=0 until false do ((x++)) if [[ $x -eq 5 ]] then break fi echo "Values are:" $x done echo "Loop Terminated" When the value of increment (“x”) equals 5, the break statement will terminate the loop, and the statements outside the loop body will execute. 7.2 The continue ...
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?
If the current cursor position is at the end of the current command, the value of this variable equals ${#COMP_LINE}. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see the section "Programmable Completion" below). ...
making them a good choice for basic array looping. ‘While’ and ‘until’ loops offer more control over the loop condition, which can be useful in more complex scenarios. However, they require you to manually manage a counter variable, which can lead to off-by-one errors if you’re not...
为true的时候, &&操作 才会返回0(代表sucess. - 选项, 前缀 在所有的命令内如果想使用选项参数的话,前边都要加上"-". COMMAND -[Option1][Option2][...] ls - sort -dfu $file set -- $variable 1 if [ $file1 -ot $file2 ] then 3 echo "File $file1 is older than $file...