如果没有if; then; fi：if内置执行shell命令，并根据命令的返回值选择块。如果ls没有找到请求的文件，则返回一个不同的状态码，因此不需要grep部分。[[utility实际上是bash中的一个内置命令IIRC，用于执行算术运算。我可能是错的，因为我很少偏离伯恩shell语法。无论如何，如果你把所有这些放在一起，那么你最终会得到以下命令：
${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}...
”while” 语句就会执行 while [ condition ] do command1 command2 command3 done 或者...
9. if [grep foo myfile] 初学者会错误地认为,[是 if 语法的一部分,正如 C 语言中的 if ()。但是事实并非如此,if 后面跟着的是一个命令,[是一个命令,它是内置命令 test 的简写形式,只不过它要求最后一个参数必须是]。下面两种写法是一样的: # POSIX if [ false ]; then echo "HELP"; fi if tes...
NAME Command name to be interpreted. ###被解读的命令名 Exit Status: Returns successifall of the NAMEs are found; failsifany are not found. ###假如所有的NAMEs都找到返回成功;假如任何一个未找到就返回失败。 typeset: typeset [-aAfFilrtux] [-p] name[=value] ... Set...
As we have created the file beforehand, the result now is0: You can also use square brackets instead of thetestcommand: [ -f /tmp/test.txt ]Copy echo $?Copy Check if a File Does not Exist Testing for a file returns0(true) if the file exists and1(false) if it does not exist. ...
if [ $mod -eq 0 ]; then echo "Number $num is even" fi The modulus operation (%) returns zero when it is perfectly divided by the given number (2 in this case). 🚧 Pay special attention to space. There must be space between the opening and closing brackets and the conditions. Si...
If a sigspec is ERR, the command arg is executed whenever a pipeline (which may consist of a single simple command), a list, or a compound command returns a non-zero exit status, subject to the following conditions. The ERR trap is not executed if the failed command is part of the co...
-bash: yum: command not found 下面所需的所有压缩包:https://download.csdn.net/download/ma950924/10687769 步骤如下 第一步: http://mirrors.163.com/centos/6/os/x86_64/Packages/ 到上面这个网站去下载如下RPM包 python-iniparse-0.3.1-2.1.el6.noarch.rpm yum-metadata-par... ...
some command"$i"done 1. 2. 3. 4. 5. 如果你有使用引号[6]和避免单词拆分[7]的习惯,你完全可以避免很多错误。 注意下循环体内部的 "$i",这里会导致下面我们要说的另外一个比较容易犯的错误。 2. cp $file $target 上面的命令有什么问题呢?如果你提前知道,$file 和 $target 文件名中不会包含空格或...