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?
shellcheck script.sh 其中,script.sh是要检测的bash脚本文件。 使用bash内置的调试功能。可以在bash脚本中添加以下代码,启用调试功能: 代码语言:txt 复制 set -x 这个命令会在每个执行的命令前打印出命令的内容,可以帮助找到程序错误。 使用trap命令。可以在bash脚本中添加以下代码,捕获程序错误并输出错误信息: 代码语...
#!/bin/bash check_program() { program_name=$1 which $program_name >/dev/null 2>&1 if [ $? -eq 0 ]; then echo "$program_name is installed." else echo "$program_name is not installed." fi } check_library() { library_name=$1 if dpkg-query -l $library_name >/dev/null ...
In programming, it is essential to check if a variable is “set” or “not set,” which means you have to check if a bash script variable has a value or not. This check helps for effective data validation. However, there’s no built-in function for checking empty variables in bash s...
Use the if-else statement with the -v option to check if an environment variable is set in bash. The echo command in the if block will be executed if the will
env | grep PATH > /dev/null if [ $? -eq 0 ] then echo "The value of Environment variable is: $PATH" else echo "Environment variable does not exist." fi This is a bash script that checks if the environment variable PATH exists and if it does, prints its value. If the PATH varia...
In Bash programming, variables play a vital part in transforming the script to a modern standard. Variables are named symbols representing a string or numeric value. When creating a Bash variable, it must have a value. However, we can set a default value
if ! type -p convert &>/dev/null; then printf '%s\n' "error: convert is not installed, exiting..." exit 1 fi使用strftime获取当前日期Bash的printf有一个内置的获取日期的方法,可用来代替date命令。警告: 要求bash版本4+示例函数:date() { # 用法: date "format" # 通过"man strftime"看格式 ...
commit new bash script Feb 24, 2018 138 139 140 141 ps -u {user} # 查看某用户进程 ps axjf # 列出进程树 ps -eo pid,user,command # 按用户指定的格式查看进程 ps aux | grep httpd # 查看名为 httpd 的所有进程 Feb 24, 2018 update bash.sh ...
Before you call mkdir, check for an empty first argument (i.e. no arguments). You can do this using Bash's if statement which runs code based on a condition: if["$1"=""];then If the first argument is empty, print an error and exit your script: ...