$(...) holds the value, not the exit status, that is why this approach is wrong. Has there been a naval battle where a boarding attempt backfired? Nice, but I prefer the Mr. shellter answer because is "self documented", is more "readable" the programmer intention. rev 2020.11.13.38000, Stack Overflow works best with JavaScript enabled, Where developers & technologists share private knowledge with coworkers, Programming & related technical career opportunities, Recruit tech talent & build your employer brand, Reach developers & technologists worldwide. 这种情况怎么了? I guess something is wrong with the () . 可用, 但是要两个独立的 [ ] , [[ ]] 或 (( ))      看 1 5 -ne 比较数字 (numberic) ; != 比较字符 (string), 但后者拿来    比较数字也可,只是不是标准用法    -lt 是等同 < , 但 < 只能在 shell 的数值操作符 (( )) 或    者 逻缉操作符 [[ ]] 才可使用, -lt , -eq , -gt , -ge    -le , 这些是 test , 就是 [ ] 这个内建命令使用的条件操    作符, 数字用, = , != 字符用, == 这个该是 [[ ]] 用的,    可用来比对正规表示式, 但用在 [ ] 也可,只是不太正统用法. This one did the job perfectly! ;-), $ grep sysa /etc/passwd || { echo "ERROR - The user sysa could not be looked up"; exit 2; }.

In this case, per a comment by Orwellophile, the arithmetic evaluation can be pared down even further, like, Finally, there is an award called the Useless Use of Cat (UUOC). Is there objective proof that Jo Jorgensen stopped Trump winning, like a right-wing Ralph Nader?
请注意, -a和-o运营商的POSIX规范的一部分test ,又名[ ,主要用于向后兼容性(因为他们的部分test在第7版UNIX等),但它们被明确标记为“过时由POSIX。 Bash (see conditional expressions ) seems to preempt the classic and POSIX meanings for -a and -o with its own alternative operators that take arguments. [ $(grep -c "sysa" /etc/passwd) -eq 0 ] ; then which works but is rather old school. 腾讯云 版权所有 京公网安备 11010802017518 粤B2-20090059-1. However, if !

That is why it needs to be rephrased to if ! your coworkers to find and share information.

I've tried to answer the specific question. It's all rather silly really, from my answer to a much harder (question)[. Podcast 286: If you could fix any software, what would you change?

-eq 1 ] then echo "blah blah blah" fi 我还面临的问题是,Exit语句位于if语句之前,它必须有退出代码,如何解决? What did Pete Stewart think he knew about efficient implementation of floating point denormals? find .

Why is "hand recount" better than "computer rescan"? Stack Overflow for Teams is a private, secure spot for you and All Rights Reserved. Thanks for your ideas. Align equivalence arrows and equal signs without weird spacing. 确保正确引用它们。, Using /bin/bash the following will work: 使用/bin/bash可以正常工作:, Classic technique (escape metacharacters): 经典技术(转义元字符):, I've enclosed the references to $g in double quotes; 我已将对$g的引用括在双引号中; that's good practice, in general. 我会这么想的。 However, there is another alternative, namely: 但是,还有另一种选择,即:, Indeed, if you read the 'portable shell' guidelines for the autoconf tool or related packages, this notation — using ' || 确实,如果您阅读了autoconf工具或相关软件包的“便携式外壳”指南,则使用- ||表示。 ' and ' && ' — is what they recommend. I would like to have the echo command executed when cat /etc/passwd | grep "sysa" is not true. @0zkrPM But the shellter version does not work in Bourne shell. i just through i would throw in a properly bounded check on username, else if the OP really does search on "sys" or somesuch, he'll get quite the surprise. [ $(true) ]; then echo false; fi would always print false because the true command does not write anything to stdout (even though the exit code is 0). By using our site, you acknowledge that you have read and understand our Cookie Policy, Privacy Policy, and our Terms of Service. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. How can I check if a directory exists in a Bash shell script? 4. 严格来说,不需要括号,因为-a和-o的优先级使得即使没有它们也正确。, Note that the -a and -o operators are part of the POSIX specification for test , aka [ , mainly for backwards compatibility (since they were a part of test in 7th Edition UNIX, for example), but they are explicitly marked as 'obsolescent' by POSIX. How can I manage a remote team member who appears to not be working their full hours? How do I split a string on a delimiter in Bash? How to concatenate string variables in Bash.

'和' && '—是他们的建议。 I suppose you could even go so far as: 我想您甚至可以做到:, Where the actions are as trivial as echoing, this isn't bad. You will get. This could happen if there is a partial or exact match somewhere else in the file. Why does Ray Bradbury use "flounder" for an action with a positive outcome? An alternative would be cat /etc/passwd | grep "sysa" || echo error. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. I want to represent multiple conditions like this: 我想代表多个条件,例如:, but when I execute the script, it shows 但是当我执行脚本时,它显示. How to get the source directory of a Bash script from within the script itself? How to specify the private SSH-key to use when executing shell command on Git? -o = or , -a = and , 但我一向只用 || 或者 && 4. In order to make sure data loggers are online a cron script runs every 15 minutes that looks like this: ...and so on for each data logger that you can see in the montage I'll just say that grep can take a file name on its cmd-line, so why invoke extra processes and pipe constructions when you don't have to? Found the other answers rather confusing, hope this helps someone. Also, looking at your code as is, your use of the $( ... ) form of cmd-substitution is to be commended, but think about what is coming out of the process. not picking on your answers, quite enjoyed them. Making statements based on opinion; back them up with references or personal experience. grep returns true if it finds the search target, and false if it doesn't. if ( ‘001’ == FormId ||'002’FormId||‘003’ FormId ){…}, 格式如下,在比较时,数字和字符串用不同的比较符号 1.如果a>b且a b )) && (( a < c ))      或者    if [[ $a > $b ]] && [[ $a < $c ]]     或者          if [ $a -gt $b -a $a -lt $c ] 2.如果a>b或a b )) || (( a < c ))              或者       if [[ $a > $b ]] || [[ $a < $c ]]        或者        if [ $a -gt $b -o $a -lt $c ] 3. #include #include int main() { int i = 0; for (i = 0;... use industry_finance; DELIMITER // drop procedure.

正则表达式中还有一个较为常用的运算符,即否定符 “[^]”。与我们前文所介绍的定位符 “^” 不同,否定符 “[^]”规定目标对象中不能存在模式中所规定的字符串。例如: /[^a-c]/ 上述字符串将会与目标对象中除a,b,和c之外的任何字符相匹配。 Trying to identify an aircraft from a photo. How to represent multiple conditions in a shell if statement? site design / logo © 2020 Stack Exchange Inc; user contributions licensed under cc by-sa.

This would provoke a valid match on things like cara and enoc etc., even though there are no such users on my system. 可用, 但是要两个独立的 [ ] , [[ ]] 或 (( ))      看 1, 5 -ne 比较数字 (numberic) ; != 比较字符 (string), 但后者拿来, 者 逻缉操作符 [[ ]] 才可使用, -lt , -eq , -gt , -ge. What happens with Jared and a dying monarch? :-) Some people will jump up and down and cry gothca! @SDsolar Your code is probably not executed by. Great! and the local password database file. "||"和"&&"在SHELL里可以用吗?也就是第一个写成if [ a>b && a How to test multiple variables against a ...21个我试图从. grep -qs..." did not work with /proc/mounts and trying to find out if a regularly dropping USB-disk was mounted on Raspbian 4.9 kernel. For a grep solution to be correct, you will need to properly parse the /etc/passwd file: ... or any other similar test against the first of the :-delimited fields. where line 15 is the one showing if .... 第15行显示的是.... What is wrong with this condition? yes, well there's solving a problem most efficiently, and then there is answering specific question. if evaluation in shells are designed to be very flexible, and many times doesn't require chains of commands (as you have written). For example, in my passwd file, there is a line saying. How can I check if a program exists from a Bash script? -name "*.txt" -print 不以.txt 结尾的 ... bash黑客都喜欢单行命令 ... 科技小先锋 2017-11-22 02:14:00 浏览1045

BUT, you could use the newest shell features (arithmetic evaluation) like.

我猜想() 。, 参考:https://stackoom.com/question/g3qx/如何在if语句中表示多个条件, Be careful if you have spaces in your string variables and you check for existence. ping -c 1 SOLAR &>/dev/null then echo "SUBJECT: SOLAR is not responding to ping" | ssmtp abc@def.com echo "SOLAR is not responding to ping" | ssmtp 4151112222@txt.att.com else echo "SOLAR is up" fi # if ! 我想知道在if语句中检查退出状态的最佳方法是什么,以便响应特定的输出。 我想的是: if [ $? The Overflow #47: How to lead with clarity and empathy in the remote world, Creating new Help Center documents for Review queues: Project overview, Feature Preview: New Review Suspensions Mod UX, have to determine all users home directories - tilde scripting problem. Georgia doing "hand recount" of 2020 Presidential Election Ballots. 1955: When Marty couldn't use the time circuits anymore was the car still actually driveable? Good luck to all. ! 如果字符串变量中有空格并检查是否存在,请格外小心。 Be sure to quote them properly. grep ...; then. 比如说,如果ssh 192.168.0.4是.bash_history其中的一行,那么$0中包含ssh 192.168.0.4,$1中包含ssh.

The issue with grep -q "$username" /etc/passwd is that it will give a false positive when there is no such user, but something else matches the pattern. https://stackoom.com/question/g3qx/如何在if语句中表示多个条件. You can take that further by using the -c (count) option to grep and then do if ! Code-only answers are discouraged on Stack Overflow because they don't explain how it solves the problem. 在动作像回声一样琐碎的情况下,这还不错。 When the action block to be repeated is multiple lines, the repetition is too painful and one of the earlier versions is preferable — or you need to wrap the actions into a function that is invoked in the different then blocks. Here is an answer by way of example: In order to make sure data loggers are online a cron script runs every 15 minutes that looks like this: #!/bin/bash # if !

To learn more, see our tips on writing great answers. Help identify, Can someone re-license my BSD-3-licensed project under the MIT license, remove my copyright notices, and list me as a "collaborator" without consent, I'm looking for a way to emulate addressable LED strip using LED diodes in a custom arrangement.

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