if!type"$foobar_command_name"> /dev/null;then# install foobar here,or poping up some warning messagesfi references: http://stackoverflow.com/questions/7522712/how-to-check-if-command-exists-in-a-shell-script http://stackoverflow.com/questions/592620/how-to-check-if-a-program-exists-from-a...
/bin/bash # Calculate the week number using the date command: WEEKOFFSET=$[ $(date +"%V") % 2 ] # Test if we have a remainder. If not, this is an even week so send a message. # Else, do nothing. if [ $WEEKOFFSET -eq "0" ]; then echo "Sunday evening, put out the gar...
一、if语句: 单分支: if CONDITION-TRUE; then 分支 fi 双分支: if CONDITION-TRUE; then 分支1 else 分支2 fi 多分支: if CONDITION1-TRUE; then 分支1 elif CONDITION2-TRUE; then 分支2 ... else 分支n fi 二、条件测试: test EXPRESSION [ EXPRESSION ] ` EXPRESSION ` COMMAND 2.1 测试表达式: ...
[student@studentvm1 testdir]$ File="TestFile1" ; touch $File ; if [ -s $File ] ; then echo "$File exists and contains data." ; else echo "$File does not exist or is empty." ; fi TestFile1 does not exist or is empty. 向文件添加一些内容,然后再测试一次: [student@studentvm1 ...
[ -n "$(some command with a "$file" in it)" ] [[ -n $foo ]] [[ -z $foo ]] 37. [[ -e "$broken_symlink" ]] returns 1 even though $broken_symlink exists 这里-e 选项是看文件是否存在,当紧跟的文件是一个软链接时,它不看软链接是否存在,而是看实际指向的文件是否存在。所以当软链...
commands from the first one that exists and is readable. The –noprofile option may be used when the shell is started to inhibit this behavior. When a login shell exits, bash reads and executes commands from the files ~/.bash_logout and /etc/bash.bash_logout, if the files exists. ...
if TEST; then CMDfi 1. 2. TEST:条件判断,多数情况下可使用test命令来实现,返回值为0的话则执行CMD,否则就离开该条件结构体,脚本继续往下执行。 [root@c7-server ~]# cat test.sh#!/bin/bashif id zwl &> /dev/null; then echo "User zwl exists."fi[root@c7-server ~]# bash test.sh User ...
如果新装的系统,运行一些很正常的诸如:shutdown,fdisk的命令时,悍然提示:bash:command not found。那么 首先就要考虑root 的$PATH里是否已经包含了这些环境变量。 主要是这四个:/bin ,/usr/bin,/sbin,/usr/sbin。 四个主要存放的东东: ./bin: bin为binary的简写主要放置一些系统的必备执行档例如:cat、cp、chmo...
来自:Linux迷链接:https://www.linuxmi.com/bash-linux-test-command.html Linux test 命令是 Shell 内置命令,用来检测某个条件是否成立。test 通常和 if 语句一起使用,并且大部分 if 语句都依赖 test。可以将一个元素与另一个元素进行比较,但它更常用于BASH shell 脚本中,作为控制逻辑和程序流程 的条件语句的...
echo "the user $1 exists" else useradd $1 echo "123456" | passwd --stdin $1 &> /dev/null echo "Add user $1 finished." fi 练习1:通过命令行参数给定两个数字,输出其中较大的数值; 解: #!/bin/bash # if [ $# -lt 2 ];then ...