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
if [ -z ${var+x} ]; then echo "var is unset"; else echo "var is set to '$var'"; fi 参考:https://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash 6、换算秒为分钟、小时 代码语言:javascript 代码运行次数:0 运行 AI代码解释 #!/bin/bash a=60100 sw...
语句我们常用于实现系统服务启动脚本等场景,case条件语句也相当于if语句多分支结构,多个选择,case看起来更规范和易读 老油条IT记 2020//04 8930 常用bash脚本功能 bashhttpsbash 指令网络安全编程算法 参考:https://overflowcom/questions/3601515/how-to-check-if-a-variable-is-set-in-bash YP小站 2021/11...
PROMPT_DIRTRIM variable) \W the basename of the current working directory, with $HOME abbreviated with a tilde \! the history number of this command \# the command number of this command \$ if the effective UID is 0, a #, otherwise a $ \nnn the character corresponding to the octal nu...
$mvvariable showvar $ ./showvar $x is not set $ x=3$ ./showvar $x is not set $ export x=4$ ./showvar $x=4$ x=## bash中,对一个变量重新赋值,并不会从环境变量中移除该变量 $ ./showvar $x is set but empty 设置在子shell中的变量对调用它的脚本不可见。子shell包含命令替换,如...
The $ENV variable is similar to the $BASH_ENV. It is used when the shell runs in POSIX compatibility mode.### Define Debug environment ### Filename: my-debug-env trap 'echo "$BASH_COMMAND" failed with error code $?' ERR #!/usr/bin/env bash #...
检测:env x='() { :;}; echo vulnerable’ bash -c “echo this is a test” UBuntu修复: apt-get update apt-get install bash 修复之后: env x='() { :;}; echo vulnerable’ bash -c “echo this is a test” bash: warning: x: ignoring function definition attempt bash: error importing...
1、查看系统存在的环境变量env 和 export env命令:查看环境变量 [CJP@CJP ~]$ env HOSTNAME=CJP SHELL=/bin/bash HISTSIZE=1000 USERNAME=CJP MAIL=/var/spool/mail/CJP PATH=/home/CJP/qtsdk-2010.05/qt/bin:/usr/lib/qt-3.3/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin...
ShellCheck will warn when using features not supported by the shebang. For example, if you set the shebang to#!/bin/sh, ShellCheck will warn about portability issues similar tocheckbashisms: echo{1..$n}# Works in ksh, but not bash/dash/shecho{1..10}# Works in ksh and bash, but ...
# shellcheck disable=SC2086,SC2048trim_all() {# Usage: trim_all " example string "set-fset-- $*printf'%s\n'"$*"set+f } 用法示例: $trim_all" Hello, World "Hello, World$name=" John Black is my name. "$trim_all"$name"John Black is my name. ...