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?
progname=${0##*/} ## Get the name of the script without its path ## Default values verbose=0 filename= ## List of options the program will accept; ## those options that take arguments are followed by a colon optstring=f:v ## The loop calls getopts until there are no more options...
而if [ ! -z err]||[!−eapk ]; then 没问题; 整数比较 : -eq 等于,如:if [ "a"−eq"b" ] -ne 不等于,如:if [ "a"−ne"b" ] -gt 大于,如:if [ "a"−gt"b" ] -ge 大于等于,如:if [ "a"−ge"b" ] -lt 小于,如:if [ "a"−lt"b" ] -le 小于等于,如:if...
使用if else bash脚本检查变量是否存在 我尝试编写一个非常简单的bash脚本文件,名为bash_script.sh。 echo $1 echo 'no variable'在终端中,我尝试运行./bash_script.sh hello,但是终端上的输出是no variable。我在这里做错了什么? 浏览1提问于2021-08-18得票数 1 回答已采纳 1回答 如何检查环境变量是否设置...
/bin/bash # declare STRING variable STRING="Hello World" #print variable on a screen echo $STRING Navigate to a directory where your hello_world.sh is located and make the file executable: $ chmod +x hello_world.sh Now you are ready to execute your first bash script:...
选择执行:if单分支、if双分支、if多分支;case语句 2、case语句: 语法格式: case $VARIABLE in //$VARIABLE是变量引用,in是关键字 PAT1) //模式1 分支1 ;; //以双分号结束分支1语句 PAT2) 分支2 ;; ... *) //所有都不匹配,为*,类似else ...
# description test_service_script prog=$(basename $0) lockfile=/var/lock/subsys/$prog case $1 in start) if [ -f $lockfile ] ;then echo "$prog is running yet." else touch $lockfile [ $? -eq 0 ] && echo "Start $prog finished.." ...
Bash, short for "Bourne Again SHell," is a powerful scripting language used in Unix-based operating systems. One of the fundamental constructs in Bash programming is the if statement. The if statement allows you to control the flow of your script based on specific conditions. In this article...
echo"Input argument exists." Here the“-eq”operator is used to check if the“$#”variable is equal to zero or not and if the “$#” variable is equal to zero, the script will display an error message and exit with a status code of 1. Otherwise, the script will continue executing,...
When bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to read and execute. Bash behaves as if the following command ...