您可以使用测试结构 [[ ]] 以及正则表达式匹配运算符 =~，检查字符串是否与正则表达式匹配.

对于你的具体情况，你可以写:

[[ $date =~ ^[0-9]{8}$ ]] &&回声是"

或者更准确的测试:

[[ $date =~ ^[0-9]{4}(0[1-9]|1[0-2])(0[1-9]|[1-2][0-9]|3[0-1])$ ]] &&回声是"# |\______/\______*______/\______*__________*______/|# |||||# |||||# |--年-- --月-- --日-- |# |要么 01...09 要么 01..09 |# 行首或 10,11,12 或 10..29 |# 或 30, 31 |#                                                        行结束

也就是说，您可以在 Bash 中定义一个与您想要的格式匹配的正则表达式.你可以这样做:

[[ $date =~ ^regex$ ]] &&回声匹配"||回声不匹配"

where && 之后的命令如果测试成功就执行，||之后的命令如果测试不成功就执行.

请注意，这是基于 Aleks-Daniel Jakimenko 在 bash 中的用户输入日期格式验证中的解决方案.>

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在其他 shell 中，您可以使用 grep.如果您的 shell 符合 POSIX，请执行

(echo "$date" | grep -Eq ^regex$) &&回声匹配"||回声不匹配"

在不符合 POSIX 的 fish 中，您可以这样做

echo "$date";|grep -Eq "^regex$";并回显匹配"；或回声不匹配"

One of the arguments that my script receives is a date in the following format: yyyymmdd.

I want to check if I get a valid date as an input.

How can I do this? I am trying to use a regex like: [0-9]{8}

You can use the test construct, [[ ]], along with the regular expression match operator, =~, to check if a string matches a regex pattern.

For your specific case, you can write:

[[ $date =~ ^[0-9]{8}$ ]] && echo "yes"

Or more a accurate test:

[[ $date =~ ^[0-9]{4}(0[1-9]|1[0-2])(0[1-9]|[1-2][0-9]|3[0-1])$ ]] && echo "yes"
#           |\______/\______*______/\______*__________*______/|
#           |   |           |                  |              |
#           |   |           |                  |              |
#           | --year--   --month--           --day--          |
#           |          either 01...09      either 01..09      |
# start of line            or 10,11,12         or 10..29      |
#                                              or 30, 31      |
#                                                        end of line

That is, you can define a regex in Bash matching the format you want. This way you can do:

[[ $date =~ ^regex$ ]] && echo "matched" || echo "did not match"

where commands after && are executed if the test is successful, and commands after || are executed if the test is unsuccessful.

Note this is based on the solution by Aleks-Daniel Jakimenko in User input date format verification in bash.

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In other shells you can use grep. If your shell is POSIX compliant, do

(echo "$date" | grep -Eq  ^regex$) && echo "matched" || echo "did not match"

In fish, which is not POSIX-compliant, you can do

echo "$date" | grep -Eq "^regex$"; and echo "matched"; or echo "did not match"