搜索关键字：

• shell test and/or
• shell multi test and/or

参考解答：

推荐使用 && 和 || 将多个简单的测试语句连接起来：

if [ -n "$var"] && [ -e "$var"]; then
    echo "\$var is not null and a file named $var exists!"
fi

使用了AND和OR的测试语句的返回值是列表中最后一个执行的命令的返回值。

• 当执行 command1 && command2 时，只有当 command1 执行成功后才会执行 command2 ；
• 当执行 command1 || command2 时，只有当 command1 执行失败后才会执行 command2 。

使用”[[“关键字（不推荐）：

[[ is a new improved version of “test/[“, and is a keyword, not a program. This makes it easier to use, as shown below. [[ is understood by KornShell, Zsh and BASH (e.g. 2.03), but not by other POSIX shell implementations (like posh, yash or dash) or the BourneShell .

[[ 是一个关键字，但只能被 KornShell、Zsh和Bash 所解释，不支持其他的POSIX shell实现，比如：posh、yash、dash或BourneShell，这样的话就不能做到通用，因此不推荐使用。

$ if [[ -n "/tmp" && -d "/tmp" ]]; then echo true; fi
true

$ if [ -n "/tmp" && -d "/tmp" ]; then echo true; fi
-bash: [: missing `]'

在 test/[ 中使用-a和-o（不推荐）：

测试命令的 AND 和 OR 逻辑操作符是 -a 和 -o ：

if [ -n "$var" -a -e "$var" ] ; then
    echo "\$var is not null and a file named $var exists"
fi

这里没有 && 和 || 的说法：

$ if [ -n "/tmp" && -d "/tmp" ]; then echo true; fi  # DOES NOT WORK
bash: [: missing `]'

In any case, avoid the -a/-o test operators which are deprecated and unreliable in the general case .

尽量避免在测试操作时使用 -a/-o 来进行多条件判断，因为它们将会被废弃，进而导致你的脚本出现问题，所以不建议在test/[中使用-a/-o进行多条件判断。

==

I want to check if [[ $var == foo || $var == bar || $var == more ]] without repeating $var n times.

The portable solution uses case:

# Bourne
case $var in
    foo|bar|more) ... ;;
esac

In Bash and ksh, Extended globs can also do this within a [[ command:

# bash/ksh
if [[ $var == @(foo|bar|more) ]]; then
    ...
fi

Alternatively, you may loop over a list of patterns, checking each individually.

# bash/ksh93
[[ -v BASH_VERSION ]] && shopt -s extglob
# usage: pmatch string pattern [ pattern ... ]
function any {
    [[ -n $1 ]] || return
    typeset pat match=$1
    shift

    for pat; do
        [[ $match == $pat ]] && return
    done

    return 1
}

var='foo bar'
if any "$var" '@(bar|baz)' foo\* blarg; then
    echo 'var matched at least one of the patterns!'
fi

For logical conjunction (return true if $var matches all patterns), ksh93 can use the & pattern delimiter.

# ksh93 only
[[ $var == @(foo&bar&more) ]] && ...

For shells that support only the ksh88 subset (extglob patterns), you may DeMorganify the logic using the negation sub-pattern operator.

# bash/ksh88/etc...
[[ $var == !(!(foo)|!(bar)|!(more)) ]] && ...

But this is quite unclear and not much shorter than just writing out separate expressions for each pattern.

参考链接：

• http://wiki.bash-hackers.org/commands/classictest#and_and_or
• http://mywiki.wooledge.org/BashPitfalls
• http://unix.stackexchange.com/questions/210763/how-to-use-and-or-conditional-in-shell-script
• http://unix.stackexchange.com/questions/88850/precedence-of-the-shell-logical-operators

=EOF=