[student@studentvm1 testdir]$ File="TestFile1" ; echo "This is $File" > $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 ...
by the 'test' builtin, and may be combined using the following operators: ( EXPRESSION ) Returns the value of EXPRESSION ! EXPRESSION True if EXPRESSION is false; else false EXPR1 && EXPR2 True if both EXPR1 and EXPR2 are true; else false EXPR1 || EXPR2 True if either EXPR1 or EX...
[ 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...
In this example, the script first checks if ‘a’ is greater than ‘b’. If it’s not, it moves on to the ‘elif’ statement to check if ‘a’ is greater than ‘c’. If neither condition is met, it executes the ‘else’ statement, which in this case, prints ‘a is not greate...
#3强调#a=1 可以a =1 不可以,变量名字和等号之间没有空格 #4格式val=`expr $a + $b` echo "a + b : $val" #5强调#乘号(*)前边必须加反斜杠(\)才能实现乘法运算 #6格式#if语句if condition1 then command1 elif condition2 then command2 else commandN fi #7格式for var in item1 item2 ....
1 : This is a comment thar generates an error,(if [ $x -eq 3] ). ":"还用来在/etc/passwd和$PATH变量中用来做分隔符. bash$ echo $PATH /usr/local/bin:/bin:/usr/X11R6/bin:/sbin:/usr/sbin:/usr/games! 取反操作符,将反转"退出状态"结果,(见Example 6-2).也会反转test操作符的意义...
Unary operators are often used to test the status of a file, a variable, a shell option (optname), or a string. Unary and Binary expressions are formed with the following primaries. Conditional ExpressionMeaning -a file True if file exists....
了 Bash let 命令,它用于执行一个或多个表达式...,变量计算中不需要加上 $ 来表示变量 #8 #until 循环 #9收获运行sh文件 bash 1.sh #10收获 tar -czvf test.tar.gz a.c //压缩 a.c文件为test.tar.gz.../bin/bash #!...<<EOF your-password EOF bash教程 linux/linux-shell-basic-operators....
The(( ))compound commandevaluates an arithmetic expression and sets the exit status to 1 if the expression evaluates to 0, or to 0 if the expression evaluates to a non-zero value. You do not need to escape operators between((and)). Arithmetic is done on integers. Division by 0 causes ...
[$1-eq"shellcheck"]# Numerical comparison of strings[$n&&$m]# && in [ .. ][ grep -q foo file ]# Command without $(..)[["$$file"== *.jpg ]]# Comparisons that can't succeed(( 1 -lt 2 ))# Using test operators in ((..))[ x ] & [ y ] | [ z ]# Accidental ...