$ unset x $ showvar $x is not set $ x=3 $ showvar $x is not set $ export x $ showvar $x = 3 $ x= ## in bash, reassignment doesn't remove a variable from the environment $ showvar $x is set but empty 注意 showvar不是一个 bash 命令,而是一个如清单 5-1 所示的脚本,...
${variable%%pattern} # if the pattern matches the end of the variable's value, delete the longest part that matches and return the rest ${variable/pattern/string} # the longest match to pattern in variable is replaced by string. Only the first match is replaced ${variable//pattern/string}...
bash shell参数展开(Shell Parameter Expansion):替换变量(variable)中的字符串 在写bash shell脚本时,如果遇到要替换变量中的字符串,首先想到的就是用sed命令,比如下面的示例将变量str中的数字123替换成UUU: $ str=hello,word,123 $ echo...$str | sed -E -e 's/[0-9]/U/g' hello,word,UUUU 上面的...
#This variable is global and can be used anywhere in this bash script VAR="global variable" function bash { #Define bash local variable #This variable is local to bash function only local VAR="local variable" echo $VAR } echo $VAR bash # Note the bash global variable did not change # ...
# set variable identifying the chroot you work in (used in the prompt below) if [ -z "${debian_chroot:-}" ] && [ -r /etc/debian_chroot ]; then debian_chroot=$(cat /etc/debian_chroot) fi # set a fancy prompt (non-color, unless we know we "want" color) ...
- Testifthe specified variable has an empty value: [[ -z$variable]] - Testifthe specified [f]ile exists: [[ -f path/to/file ]] - Testifthe specified [d]irectory exists: [[ -d path/to/directory ]] - Testifthe specified file or directory [e]xists: ...
While ShellCheck is mostly intended for interactive use, it can easily be added to builds or test suites. It makes canonical use of exit codes, so you can just add ashellcheckcommand as part of the process. For example, in a Makefile: ...
Used in filename expansion and string manipulation. <( ) It is very similar to a pipe and used for process substitution. { } Used to expand sequences. ${ } Used for string manipulation and variable interpolation. | Used to run multiple commands together.| > Used to send output to a fi...
[root@localhost ~]# ls *.shinit_use.sh mysql_bak.sh 1. 2. 通配符是系统shell层次(level的),由shell负责解释, 而正则表达式需要相关工具的支持: egrep, awk, vi, perl。 在文本过滤工具里,都是用正则表达式,比如像awk,sed等,是针对文件的内容的。
Note:There should not be any space around “=” sign in variable assignment. When you use VAR=VALUE, shell sees the “=” as a symbol and treats the command as a variable assignment. When you use VAR = VALUE, shell assumes that VAR must be the name of a command and tries to execut...