什么为在bash条件语句的最佳实践检查多条语句的时候？ [英] whats the best practice for conditionals in bash when checking multiple statements?

问题描述

鉴于你尝试检查一个变量是不是空的，而不是其他一些价值在以下code：

Given your trying to check that a variable is not empty and not some other value as in the following code:

if [ ! -z "$foo" ] && [[ ${foo} != "bar" ]]; then

什么是实现这一目标的最佳做法。我见过的bash条件语句写几种方法包括如下...

what is the best practice for accomplishing this. I've seen bash conditionals written several ways including the following...

if [[ ! -z "$foo" && ${foo} != "bar" ]]; then

据我所知，是使用单支架和双的时候，我更关心的是，当把＆放有差别;＆安培; 或 || 括号内或缩小。

推荐答案

将＆放大器;＆安培; / || 为 [[]] 。外面是可以接受的。

Put &&/|| inside brackets for [[ ]]. Outside is also accepted.

将＆放大器;＆安培; / || 括号外的 [] 。里面是不允许的。

Put &&/|| outside brackets for [ ]. Inside is NOT allowed.

这是由于这一事实，即＆放大器;＆安培; 根据返回值，例如正常结合在一起的命令

This is due to the fact that && binds normal commands together based on return value, e.g.

wget file && echo "Success"

[，尽管它的有趣的名字，是一个普通的命令，并遵守相同的规则，例如的wget 或回声。

[, despite its funny name, is a regular command and obeys the same rules as e.g. wget or echo.

[富||巴] 是两个命令， [富和巴] ，这两者都不是有效的

[ foo || bar ] is two commands, [ foo and bar ], neither of which are valid.

[[..]] ，另一方面是不是一个正常的命令，但特殊的shell语法。 [富||巴]] 是一个单一的命令，除$ P $据此ptted。

[[ .. ]] on the other hand is not a normal command but special shell syntax. [[ foo || bar ]] is a single command, and interpretted accordingly.

这篇关于什么为在bash条件语句的最佳实践检查多条语句的时候？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！