24[ FILE1 -ef FILE2 ] 如果 FILE1 和 FILE2 指向相同的设备和节点号则为真。25[ -o OPTIONNAME ] 如果 shell选项 “OPTIONNAME” 开启则为真。26[ -z STRING ] “STRING” 的长度为零则为真。27[ -n STRING ] or [ STRING ] “STRING” 的长度为非零 non
[ ARG1 OP ARG2 ] “OP” is one of -eq, -ne, -lt, -le, -gt or -ge. These arithmetic binary operators return true if “ARG1” is equal to, not equal to, less than, less than or equal to, greater than, or greater than or equal to “ARG2”, respectively. “ARG1” and “AR...
echo'C'elif test $i-gt0;then #如果i>0echo'D'elif test $i-lt0;then #如果i<0echo'invalid'else#i==0的情况 echo'zero'fi 注:if test 条件; then 语句 fi 这是基本格式,注意条件后的;不可省略,另外结束符号是fi(即:把if倒过来,有点回文的理念),另外要记住一堆缩写 -lt 即-Less Than的缩写...
String Not Equal To [[ $fruit != "banana" ]] ! Not [[ ! "apple" =~ ^b ]] If和Else 条件表达式的功能非常强大,因为我们可以使用它们来控制正在编写的Bash程序的执行方式。Bash编程中的基本构造之一是IF语句。在IF语句中编写的代码只在某个条件为真时执行,否则代码将被跳过。让我们写一个带有IF语句...
" Condition returned 0 # Test for variable length equal to zero with myVar unset [me@linux ~]$ [[ -n $myVar ]] ; echo "Condition returned $?" Condition returned 1 # Test for variable length with myVar set [me@linux ~]$ myVar="test" [me@linux ~]$ [[ -z $myVar ]] ; echo ...
echo "Count is zero or negative." fi Example 2: String Comparison !/bin/bash name="Alice" if [ "$name" == "Alice" ] then echo "Hello, Alice!" else echo "You are not Alice." fi Example 3: File Check #!/bin/bash file_path="/path/to/file.txt" ...
/bin/bash #Set the variable which equal to zero prev_count=0 count=$(grep -i "`date --date='yesterday' '+%b %e'`" /var/log/messages | egrep -wi 'warning|error|critical' | wc -l) if [ "$prev_count" -lt "$count" ] ; then # Send a mail to given email id when errors ...
[ ARG1 OP ARG2 ] “OP” is one of -eq, -ne, -lt, -le, -gt or -ge. These arithmetic binary operators return true if “ARG1” is equal to, not equal to, less than, less than or equal to, greater than, or greater than or equal to “ARG2”, respectively. “ARG1” and “AR...
If the exit status code is not equal to zero, an error message is printed. Otherwise, a success message is printed.#!/bin/bash #Take a Linux command name echo -n "Enter a command: " read cmd_name #Run the command $cmd_name #Check whether the command is valid or invalid if [ ...
Open up you favorite text editor and a create file called hello_world.sh. Insert the following lines to a file: NOTE:Every bash shell script in this tutorial starts withshebang:"#!"which is not read as a comment. First line is also a place where you put your interpreter which is in...