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长春网站建设开发的有哪些,ps素材网,广州网站优化价格,电商网站seo方案注#xff1a;本文为 “Linux | Bash Shebang” 相关应用讨论合辑。 英文引文#xff0c;机翻未校。 如有内容异常#xff0c;请看原文。 What is the preferred Bash shebang (“#!”)? 哪种 Bash Shebang#xff08;#!#xff09;写法更推荐使用#xff1f; Is ther…注本文为 “Linux | Bash Shebang” 相关应用讨论合辑。英文引文机翻未校。如有内容异常请看原文。What is the preferred Bash shebang (“#!”)?哪种 Bash Shebang#!写法更推荐使用Is there anyBashshebang objectively better than the others for most uses?是否存在一种 Bash Shebang 写法在大多数使用场景下都客观优于其他写法#!/usr/bin/env bash#!/bin/bash#!/bin/sh#!/bin/sh -etcI vaguely recall a long time ago hearing that adding a dash to the end prevents someone passing a command to your script, but can’t find any details on that.我隐约记得很久以前听说过在 Shebang 末尾添加短横线可以防止他人向脚本传入恶意命令但目前找不到相关细节说明。edited Sep 4, 2022 at 19:56Rob Bednarkasked Apr 29, 2012 at 21:37bgibson13And its/usr/local/bin/bashon OpenBSD.在 OpenBSD 系统中bash 的路径是/usr/local/bin/bash。– jwwCommentedMar 5, 2016 at 1:478Adding the dash is meant to prevent a certain kind of setuid root spoofing attacks, see添加短横线的目的是防范特定类型的 SetUID 根权限欺骗攻击详情参见security.stackexchange.com/questions/45490/…– Vladislav IvanishinCommentedAug 16, 2021 at 16:0422I would upvote this, but it has a score of 1337 and I don’t want to disturb it!我本想给这个回答点赞但它的评分正好是 1337我不想破坏这个数字– Thomas G Henry LLCCommentedFeb 3, 2022 at 18:243#!/usr/bin/env bashposes a privilege escalation security threat when a suid program executes a bash script that has such a shebang. The user can simply manipulate hisPATHand get an arbitrary bash executable to be run instead, with elevated privileges.当一个 SetUID 程序执行采用#!/usr/bin/env bash作为 Shebang 的 Bash 脚本时该写法会带来权限提升的安全风险。用户只需操纵自身的PATH环境变量就能让脚本以高权限执行任意指定的 bash 可执行文件。– EricCommentedMay 21, 2022 at 22:381Note that the answer is very dependent on whether or not your script actually needs to be abashscript (relying onbashextensions) or if any (POSIX)shwould do.需要注意的是选择哪种 Shebang 写法很大程度上取决于你的脚本是否真的需要是Bash 脚本即是否依赖 Bash 的扩展语法还是使用任意一款符合 POSIX 标准的sh解释器即可运行。– mtraceurCommentedDec 27, 2022 at 13:17Answers回答内容You should use#!/usr/bin/env bashfor portability: Different *nixes putbashin different places, and using/usr/bin/envis a workaround to run the firstbashfound on thePATH.Andshis notbash.为了保证可移植性你应当使用#!/usr/bin/env bash不同类 Unix 系统会将 bash 安装在不同路径下而使用/usr/bin/env可以作为一种兼容方案自动调用PATH环境变量中找到的第一个 bash 解释器。另外需要明确的是sh并不是bash。edited May 23, 2023 at 13:42Matthias Braunanswered Apr 30, 2012 at 12:14l0b0CommentsbgibsonThanks. Also looks like adding - to the end of $!/usr/bin/env bash - won’t do anything since only one argument is allowed by *nix in the shebang, and that is used by ‘bash’. That’s apparently only useful for preventing malicious arguments being passed to the script on the commandline if the script’s shebang is one of the others with no arguments (/bin/sh, etc).bgibson感谢解答。另外我发现在#!/usr/bin/env bash末尾添加短横线写成#!/usr/bin/env bash -并没有实际作用因为类 Unix 系统规定 Shebang 中仅允许传递一个参数且该参数会被bash占用。显然只有当脚本的 Shebang 采用无参数写法如/bin/sh等时添加短横线才有助于防止恶意参数通过命令行传入脚本。ptiernoRaybashdoesn’t live in/binon all systems.Ray 并非所有系统的bash都安装在/bin路径下。OylexSame for me, I just added it to an alias:alias shebangecho #!/usr/bin/env bash, now I just have to open the terminal and type shebang instead of going here.Oylex我也是这么做的我给它设置了一个别名alias shebangecho #!/usr/bin/env bash现在我只需打开终端输入shebang就能生成不用再专门查资料了。darkfelineThis answer is deceptive. POSIX does not say thatenvis at/usr/bin/env. It could be at/bin/envor anywhere in fact, as long as it is in the path. It could be at/dummy/envif/dummyis inPATH. Shebang itself is undefined under POSIX, so I could make#!stop toasterstart the USB coffee machine and be POSIX compliant. So#!/usr/bin/env bashisn’t particularly better than#!/bin/bash, it could be less portable depending.darkfeline这个回答有误导性。POSIX 标准并未规定env必须位于/usr/bin/env实际上它可以在任何路径下只要该路径被加入PATH环境变量即可。比如如果/dummy在PATH中env也可以在/dummy/env路径下。Shebang 本身在 POSIX 标准中并没有明确定义因此我甚至可以让#!stop toaster这条指令启动 USB 咖啡机且依然符合 POSIX 标准。所以#!/usr/bin/env bash并不见得比#!/bin/bash更好在某些情况下它的可移植性反而更差。l0b0darkfeline Portability isn’t absolute - it is mathematically impossible to make any script that will do the same thing on every platform. As of 2012 through 2018/usr/bin/envexists on more machines than either of/bin/bashxor/usr/bin/bash, so a script that starts with this line willdo the expected thing on as many machines as possible.l0b0darkfeline 可移植性并非绝对的——从数学角度来说不可能写出一个能在所有平台上实现相同功能的脚本。2012 至 2018 年的数据显示配备/usr/bin/env的设备数量要多于仅配备/bin/bash或仅配备/usr/bin/bash的设备数量因此采用该写法的脚本能够在尽可能多的设备上按预期运行。On most but not all systems, I recommend using:在大部分但不是全部系统中我推荐使用#!/bin/bashIt’s not 100% portable (some systems placebashin a location other than/bin), but the fact that a lot of existing scripts use#!/bin/bashpressures various operating systems to make/bin/bashat least a symlink to the main location.这种写法并非 100% 可移植有些系统会将bash安装在/bin以外的路径但由于大量现有脚本都采用#!/bin/bash写法这就迫使各类操作系统将/bin/bash至少设置为指向主安装路径的符号链接。The alternative of:也有人推荐另一种写法#!/usr/bin/env bashhas been suggested – but there’s no guarantee that theenvcommand is in/usr/bin(and I’ve used systems where it isn’t). Furthermore, this form will use the first instance ofbashin the current user’s$PATH, which might not be a suitable version of the Bash shell.但这种写法无法保证env命令一定位于/usr/bin我就用过env不在该路径的系统。此外这种写法会调用当前用户$PATH环境变量中找到的第一个bash而这个bash未必是合适的版本。(But/usr/bin/envshould work on any reasonably modern system, either becauseenvis in/usr/binor because the system does something to make it work. The system I referred to above was SunOS 4, which I probably haven’t used in about 25 years.)不过在所有现代化程度尚可的系统中/usr/bin/env写法都能正常工作——要么是因为env本身就在/usr/bin路径要么是因为系统会做兼容处理来确保该写法生效。我之前提到的那个特殊系统是 SunOS 4距今大概已经有 25 年没再用过了。If you need a script to run on a system that doesn’t have/bin/bash, you can modify the script to point to the correct location (that’s admittedly inconvenient).如果需要让脚本在没有/bin/bash路径的系统上运行你可以修改脚本中的 Shebang 指向正确路径诚然这种做法会比较麻烦。I’ve discussed the tradeoffs in greater depth in my answe to this question.关于这种写法的利弊权衡我在 这个问题的回答中有更深入的探讨。见下文A somewhat obscure update: One system I use, Termux, a desktop-Linux-like layer that runs under Android, doesn’t have/bin/bash(bashis/data/data/com.termux/files/usr/bin/bash) – but it has special handling to support#!/bin/bash.补充一个比较冷门的情况我使用的 Termux 系统一款运行在 Android 上的类桌面 Linux 环境本身没有/bin/bash路径其bash路径为/data/data/com.termux/files/usr/bin/bash但该系统做了特殊处理以支持#!/bin/bash写法。UPDATE: As Edward L. points out in a comment, bash is not part of the “base OS” on FreeBSD, and even if it’s installed by default, it probably won’t be installed as/bin/bash. On such a system, you can either use the#!/usr/bin/envtrick (I’m assuming that FreeBSD installedenvas/usr/bin/env), or you can use the path where bash is installed (apparently that’s#!/usr/local/bin/bash). If your scripts are only intended to run under FreeBSD, you can use#!/usr/local/bin/bash. If they’re meant to be portable, you can use the#!/usr/bin/envtrick (which has some disadvantages; see my answer cited above) or you can update the#!line when you install your scripts.更新正如 Edward L. 在评论中指出的bash 并非 FreeBSD 系统的“基础操作系统组件”即便它默认被安装其路径也大概率不是/bin/bash。在这类系统上你可以选择两种方案一是使用#!/usr/bin/env兼容写法我假设 FreeBSD 系统的env位于/usr/bin/env二是直接使用 bash 的实际安装路径显然是#!/usr/local/bin/bash。如果脚本仅用于 FreeBSD 系统可直接使用#!/usr/local/bin/bash如果需要保证可移植性则可以使用#!/usr/bin/env写法该写法存在一些弊端详见我之前引用的回答或在安装脚本时手动修改#!行内容。There may well be similar issues on some other operating systems.其他部分操作系统也可能存在类似情况。edited Feb 20, 2024 at 20:28answered Oct 17, 2018 at 17:49Keith ThompsonCommentsSoftware Engineer2-years later and this is still the best advice here. If the simple solution doesn’t work then you’ve got to question your earlier decisions. The accepted and most upvoted answer isn’t wrong, it’s just not rightSoftware Engineer两年过去了这依然是这里最实用的建议。如果简单的方案行不通那你就得重新审视之前的决策了。目前获赞最高且被采纳的回答不能算错只是并非完全准确而已mtraceurTermux has special handling for#/use/bin/envtoo, right?Termux 系统对#!/usr/bin/env写法也做了特殊处理对吧Keith Thompsonmtraceur Yes, it does – and I just discovered that the special handling works on the command line, not just on a#!line.Keith Thompsonmtraceur 是的而且我刚刚发现这种特殊处理不仅适用于#!行在命令行中同样有效。SeamusThis works, but the reason it works (at least on Debian-based systems) is because/binhas only the following symlink:lrwxrwxrwx 1 root root 7 Jul 4 00:04 /bin - usr/bin. IOW, I still feel the most upvoted answer here is the “best” answer.这种写法确实有效但究其原因至少在基于 Debian 的系统中是因为/bin目录下存在这样一条符号链接lrwxrwxrwx 1 root root 7 Jul 4 00:04 /bin - usr/bin。换句话说我依然认为目前获赞最高的回答才是“最优解”。mattmc3If you’re planning to run bash scripts on MacOS, this is bad advice.#!/bin/bashwill be perpetually stuck at 3.2.57, which is from 2014. Using#!/bin/bashonly works when you’re sure you’re deploying your script to a system that keeps its system bash modern.#!/usr/bin/env bashallows the user running your script have control of pointing to a modern userland bash, instead of a fixed and possibly outdated system bash. Otherwise, you’ll have to limit your scripts to POSIX sh (which really is ideal for portability anyway), or only older bash features.如果你的脚本要在 macOS 系统上运行那这个建议就不太适用了。macOS 系统的/bin/bash版本会一直停留在 3.2.57该版本发布于 2014 年。只有当你确定脚本的部署目标系统会保持系统自带 bash 版本较新时#!/bin/bash写法才适用。而#!/usr/bin/env bash写法则允许运行脚本的用户自行指定使用现代的用户态 bash 版本而非系统中固定且可能过时的 bash 版本。否则你就只能将脚本限制在 POSIX sh 标准语法范围内这种写法其实才是可移植性的理想选择或者仅使用 bash 的旧版特性。/bin/shis usually a link to the system’s default shell, which is oftenbashbut on, e.g., Debian systems is the lighter weightdash. Either way, the original Bourne shell issh, so if your script uses somebash(2nd generation, “Bourne Again sh”) specific features ([[ ]]tests, arrays, various sugary things, etc.), then you should be more specific and use the later. This way, on systems where bash is not installed, your script won’t run. I understand there may be an exciting trilogy of films about this evolution…but that could be hearsay./bin/sh通常是指向系统默认 Shell 的符号链接这个默认 Shell 很多时候是bash但在部分系统如 Debian中则是更轻量的dash。无论哪种情况最初的 Bourne Shell 都是sh因此如果你的脚本使用了bash第二代 Shell全称 “Bourne Again sh”的特有特性如[[ ]]条件测试、数组、各类语法糖等就应该明确指定使用 bash 的 Shebang 写法。这样一来如果目标系统未安装 bash脚本就不会被错误执行。我听说有一部关于 Shell 演化史的精彩三部曲电影……不过这可能只是传闻。Also note that when evoked assh,bashto some extent behaves as POSIX standardsh(see also the GNU docs about this).另外需要注意的是当bash以sh模式被调用时其行为在一定程度上会符合 POSIX 标准Bash-POSIX-Mode。edited Sep 20, 2018 at 11:15answered Apr 29, 2012 at 21:39wholerabbitCommentsjwwThe Public Domain Korn Shell (pdksh) is default on OpenBSD.OpenBSD 系统的默认 Shell 是公共领域 Korn Shellpdksh。aijMost systems willnotlink/bin/shto anywhere in/usras that would make it rather hard for the init scripts to run before/usris mounted.大部分系统不会将/bin/sh链接到/usr目录下的任何路径因为这样会导致/usr分区挂载完成前初始化脚本难以正常运行。wholerabbitaij I don’t know why I put “many or most” there – I’m a fedora user, where/binand/sbinfor years have just been symlinks by default, to/usr/binand/usr/sbin, so in that context/bin/shis a link tobashand the actual directory is/usr/bin. But I’ll correct the above.aij 我也不清楚当时为什么会写“很多或大部分”——我自己是 Fedora 用户该系统多年来默认将/bin和/sbin设为指向/usr/bin和/usr/sbin的符号链接因此在这个环境下/bin/sh是指向bash的链接其实际路径位于/usr/bin。不过我会修正上面的表述。38Using a shebang line to invoke the appropriate interpreter is not just for BASH. You can use the shebang for any interpreted language on your system such as Perl, Python, PHP (CLI) and many others. By the way, the shebang通过 Shebang 行调用对应解释器的用法并不仅限于 BASH。你可以为系统中的任意解释型语言设置 Shebang例如 Perl、Python、PHP命令行版本等。顺便提一句如下 Shebang 写法#!/bin/sh -(it can also be two dashes, i.e.--) ends bash options everything after will be treated as filenames and arguments.也可以使用两个短横线即--会终止 bash 的参数解析短横线之后的所有内容都会被视为文件名和参数。Using theenvcommand makes your script portable and allows you to setup custom environments for your script hence portable scripts should use使用env命令既可以提升脚本的可移植性又能为脚本配置自定义运行环境因此可移植脚本应采用如下写法#!/usr/bin/env bashOr for whatever the language such as for Perl对于其他语言同理例如 Perl 语言可写为#!/usr/bin/env perlBe sure to look at themanpages forbash:请务必查阅bash和env的手册页man bashandenv:man envNote: On Debian and Debian-based systems, like Ubuntu,shis linked todashnotbash. As all system scripts usesh. This allows bash to grow and the system to stay stable, according to Debian.注意在 Debian 及其衍生系统如 Ubuntu中sh被链接到dash而非bash。Debian 官方表示这是因为所有系统脚本都使用sh解释器这样的设置既能让 bash 持续迭代更新又能保障系统稳定性。Also, to keep invocation *nix like I never use file extensions on shebang invoked scripts, as you cannot omit the extension on invocation on executables as you can on Windows. The file command can identify it as a script.此外为了遵循类 Unix 系统的调用习惯我从不给通过 Shebang 执行的脚本添加文件扩展名——这一点和 Windows 不同Windows 系统执行可执行文件时不能省略扩展名。你可以使用file命令来识别脚本文件的类型。edited Apr 14, 2017 at 11:00nbroanswered Oct 26, 2016 at 19:55Jamie R Robillard Sr.Why is #!/usr/bin/env bash superior to #!/bin/bash?为什么#!/usr/bin/env bash优于#!/bin/bashI’ve seen in a number of places, including recommendations on this site (What is the preferred Bash shebang?), to use#!/usr/bin/env bashin preference to#!/bin/bash. I’ve even seen one enterprising individual suggest using#!/bin/bashwaswrongand bash functionality would be lost by doing so.我在很多地方都看到过推荐——包括本站的相关回答哪种 Bash Shebang 写法更推荐使用——优先使用#!/usr/bin/env bash而非#!/bin/bash。我甚至还看到有观点激进的人提出#!/bin/bash写法是错误的认为使用该写法会导致 bash 的部分功能无法使用。All that said, I use bash in a tightly controlled test environment where every drive in circulation is essentially a clone of a single master drive. I understand the portability argument, though it is not necessarily applicable in my case. Is there any other reason to prefer#!/usr/bin/env bashover the alternatives and, assuming portability was a concern, is there any reason using it could break functionality?尽管如此我使用 bash 的场景是一个严格受控的测试环境所有在用的驱动器本质上都是同一个主驱动器的克隆副本。我理解可移植性方面的考量但这一点在我的使用场景中并不一定适用。除了可移植性之外是否还有其他理由让我们优先选择#!/usr/bin/env bash写法另外如果确实需要考虑可移植性使用该写法是否存在导致功能异常的风险edited May 23, 2017 at 12:26asked Feb 6, 2014 at 20:09spugm1r313It isn’t necessarily better. See [this question and my answer on unix.stackexchange.com. (I’d vote to close this as a duplicate, but I don’t think you can do that across sites.)这种写法未必更优。可以参考 Unix Stack Exchange 上的这个问题以及我的回答(见下文。我本想将这个问题标记为重复问题关闭但跨站点标记应该是不支持的。– Keith ThompsonCommentedFeb 6, 2014 at 20:443In addition to zigg’s answer,envmay not be located at/usr/bin. Shebang comments are altogether a bad idea IMHO. If your default script interpreter doesn’t handle shebang comments, it is just a comment. However, if you know the script interpreter can handle shebang comments, and you know the path to bash, there is no reason not to invoke it using its absolute path unless the path is too long (unlikely), or you might possibly port the script to a system that doesn’t have bash located in /bin. Then again, the caveats I previously mentioned apply in that case since it involves portability.补充一下 zigg 的回答env命令不一定位于/usr/bin路径。在我看来Shebang 注释从根本上来说就不是一种理想的方案。如果系统的默认脚本解释器不支持 Shebang 注释那它就只是一条普通注释。但如果你确定脚本解释器支持 Shebang 注释且明确知道 bash 的路径那么除非路径过长这种情况可能性不大或者你可能需要将脚本移植到 bash 不在/bin路径的系统否则没有理由不使用绝对路径调用 bash。当然在涉及可移植性的情况下我之前提到的那些注意事项依然适用。– user539810CommentedFeb 6, 2014 at 20:491KeithThompson, thanks for the link. Perhaps my search to an answer before posting the question was a little narrow. My take-away from all this:KeithThompson 感谢提供链接。或许我在提问前的搜索范围有点窄了。我从这些内容中得到的结论是(1) linux/unix/posix/etc… is gray, andLinux、Unix、POSIX 等相关技术领域的很多问题并没有绝对标准的答案(2) anyone claiming to absolutely have the right answer absolutely has the right answer for their particular scenario.任何声称自己的方案绝对正确的人其方案也仅适用于他自己的特定场景。– spugm1r3CommentedFeb 6, 2014 at 20:594The behavior of many things in POSIX/Unix is well defined. The locations are not always so clear cut. Somethings have to exist like/etcor/bin/sh.bashis an add-on for most Unix like systems. It is only Linux wherebashis guaranteed to be in/binand most likely also linked as/bin/sh. Since Linux became the modern de facto Unix for a lot of people the fact that systems other than Linux might exist has been forgotten. In my own answer below I assumed Linux because you saidbash. A lot of the BSD boxes I have worked with did not even have it installed.POSIX/Unix 系统中很多功能的行为都是有明确标准的但各类程序的安装路径却并非总是清晰明确。有些路径是系统必须具备的比如/etc或/bin/sh。而bash对大多数类 Unix 系统来说都属于附加组件。只有在 Linux 系统中bash才被保证安装在/bin路径且大概率会被链接为/bin/sh。由于 Linux 已经成为很多人眼中现代 Unix 的事实标准大家很容易忽略 Linux 之外的其他系统的存在。我在下面的回答中默认基于 Linux 系统展开因为你提到了bash。我接触过的很多 BSD 系统甚至都没有安装bash。– Sean PerryCommentedFeb 6, 2014 at 21:267Keith - In the case of Bash (as opposed to Python in the other questions)… OpenBSD does not have a/bin/bash. Bash is not installed by default. If you want it, you have topkg install bash. Once installed it is located at/usr/local/bin/bash. There is nothing installed at/bin/bashon OpenBSD. A shebang of#!/bin/bashwill error, and#!/usr/bin/env bashwill succeed.Keith —— 就 Bash 的情况而言和其他问题中提到的 Python 不同……OpenBSD 系统并没有/bin/bash路径bash 也不是默认安装的组件。如果需要使用 bash必须手动执行pkg install bash命令安装。安装完成后其路径为/usr/local/bin/bash。OpenBSD 系统的/bin路径下根本没有 bash 相关文件。因此采用#!/bin/bash写法的脚本会执行报错而#!/usr/bin/env bash写法则可以正常运行。– jwwCommentedMay 12, 2019 at 15:26Answers回答内容#!/usr/bin/envsearchesPATHforbash, andbashis not always in/bin, particularly on non-Linux systems. For example, on my OpenBSD system, it’s in/usr/local/bin, since it was installed as an optional package.#!/usr/bin/env会在PATH环境变量中搜索bash而bash并非总是安装在/bin路径——在非 Linux 系统中尤其如此。例如我使用的 OpenBSD 系统bash 是作为可选包安装的其路径为/usr/local/bin。If you are absolutely surebashis in/binand will always be, there’s no harm in putting it directly in your shebang—but I’d recommend against it because scripts and programs all have lives beyond what we initially believe they will have.如果你能绝对确定bash位于/bin路径且未来永远不会改变那么直接在 Shebang 中使用绝对路径也并无不妥——但我依然不推荐这种写法因为脚本和程序的使用周期往往会超出我们最初的预期。answered Feb 6, 2014 at 20:12Mattie BCommentsJulio Guerrawhat aboutenvlocation ? POSIX does not force it.那env命令的路径问题怎么解决呢POSIX 标准并没有强制规定它的位置。ddekanyzigg That’s so UN*X… -: I mean, it’s in their best interest to have a standard location forenv, but somehow not to have a standard location (which can just be a soft link) forbash. Not to mention, why then hashbang doesn’t accept just#!bash, and use thePATH, instead of we doing exactly the same withenv. Not confusing enough for rookies, I guess.zigg 这可太有 Unix 风格了……-: 我的意思是为env设定一个标准路径明明是很合理的做法但不知为何大家却不给bash设定标准路径其实只需要设置一个符号链接就行。更不用说既然 Shebang 可以通过env实现基于PATH的解释器查找那为什么不直接支持#!bash这种写法让系统自动在PATH中搜索呢。我猜可能是觉得这样对新手来说还不够“绕”吧。Keith ThompsonXaviMontero: I’ve used a system whereenvwas in/bin, not in/usr/bin(not sure which one, likely SunOS 4). These days it’s very likely/usr/bin/envwill be available, just because of the popularity of the#!/usr/bin/envhack.XaviMontero我用过一个env命令位于/bin而非/usr/bin的系统具体是哪款系统记不清了大概率是 SunOS 4。不过如今得益于#!/usr/bin/env这种写法的广泛使用绝大多数系统都配备了/usr/bin/env路径。Kevinddekany, at first I agreed with you, but then I thought about differences betweenbashandenv. I would wager that it is much more likely for a system have or support multiple types of shells (sh,csh,tsh,zsh,fish,bash, …) and multiple versions of shells (bash 3 vs bash 4) than it is for there to multipleenvprograms. …Still true that knowing these differences does not lend well to beginners being able to delve in.ddekany 一开始我是赞同你的观点的但后来我仔细想了想bash和env的区别。我敢打赌一个系统同时存在或支持多种 Shell如sh、csh、tsh、zsh、fish、bash等以及多个 Shell 版本如 bash 3 和 bash 4的概率要远高于同时存在多个env程序的概率。……不过话说回来这些技术细节确实让新手很难上手。MatrixManAtYrServiceMarco The insecure practice here is relying on binaries to behave like you’d expect just because they happen to have a particular filepath. NixOS puts nothing at/bin/bash(or anywhere else with a conventional path) precisely so that applications are forced to be explicit about their dependencies and not just run whatever they find at a conventional spot. Who knows what crazy stuff users have sprinkled around their systems./usr/bin/envby contrast, lets users configure the PATH to control which versions should run in which circumstances. I’d argue that that’s a more secure way.Marco 这种写法的不安全之处在于它仅仅根据文件路径来假定二进制程序的行为符合预期。NixOS 系统就故意不在/bin/bash或其他任何常规路径放置任何程序其目的就是强制应用明确声明自身依赖而不是随意运行在常规路径下找到的程序。毕竟谁也不知道用户会在自己的系统里安装些什么奇奇怪怪的东西。相比之下/usr/bin/env写法允许用户通过配置PATH环境变量来控制不同场景下使用的程序版本。我认为这种方式反而更安全。The standard location of bash is/bin, and I suspect that’s true on all systems. However, what if you don’t like that version of bash? For example, I want to use bash 4.2, but the bash on my Mac is at 3.2.5.bash 的标准安装路径是/bin而且我猜测所有系统都是如此。但如果系统自带的 bash 版本不符合你的需求该怎么办比如我想使用 bash 4.2 版本但我的 Mac 电脑上自带的 bash 版本却是 3.2.5。I could try reinstalling bash in/binbut that may be a bad idea. If I update my OS, it will be overwritten.我可以尝试将 bash 重新安装到/bin路径但这很可能是个糟糕的主意——因为一旦我更新操作系统这个路径下的 bash 就会被系统自带版本覆盖。However, I could install bash in/usr/local/bin/bash, and setup my PATH to:不过我可以将 bash 安装在/usr/local/bin/bash路径并将PATH环境变量配置为PATH/usr/local/bin:/bin:/usr/bin:$HOME/binNow, if I specifybash, I don’t get the old cruddy one at/bin/bash, but the newer, shinier one at/usr/local/bin. Nice!这样一来当我在终端输入bash命令时调用的就不再是/bin/bash路径下老旧的版本而是/usr/local/bin路径下更新、更完善的版本了。完美Except my shell scripts have that!# /bin/bashshebang. Thus, when I run my shell scripts, I get that old and lousy version of bash that doesn’t even have associative arrays.但问题在于我的 Shell 脚本使用的 Shebang 是#!/bin/bash。因此当我运行这些脚本时调用的依然是那个老旧的 bash 版本——连关联数组功能都没有。Using/usr/bin/env bashwill use the version of bash found in my PATH. If I setup my PATH, so that/usr/local/bin/bashis executed, that’s the bash that my scripts will use.而使用/usr/bin/env bash写法脚本就会调用PATH环境变量中找到的 bash 版本。只要我配置好PATH让系统优先执行/usr/local/bin/bash我的脚本就会使用这个新版本的 bash。It’s rare to see this with bash, but it is a lot more common with Perl and Python:这种情况在 bash 中其实并不多见但在 Perl 和 Python 语言中却非常普遍Certain Unix/Linux releases which focus onstabilityare sometimes way behind with the release of these two scripting languages. Not long ago, RHEL’s Perl was at 5.8.8 – an eight year old version of Perl! If someone wanted to use more modern features, you had to install your own version.部分主打稳定性的 Unix/Linux 发行版其自带的 Perl 和 Python 版本往往会严重滞后。就在不久前RHEL 系统自带的 Perl 版本还是 5.8.8——这是一个已经发布了 8 年的旧版本如果用户想要使用较新的语言特性就必须手动安装新版本。Programs like Perlbrew and Pythonbrew allow you to install multiple versions of these languages. They depend upon scripts that manipulate your PATH to get the version you want. Hard coding the path means I can’t run my script underbrew.Perlbrew 和 Pythonbrew 这类工具可以让用户安装同一语言的多个版本它们的工作原理就是通过脚本修改PATH环境变量从而调用用户指定的语言版本。如果在 Shebang 中硬编码路径就无法在这类工具的环境中运行脚本了。It wasn’t that long ago (okay, it was long ago) that Perl and Python were not standard packages included in most Unix systems. That meant you didn’t know where these two programs were installed. Was it under/bin?/usr/bin?/opt/bin? Who knows? Using#! /usr/bin/env perlmeant I didn’t have to know.其实就在不算太久以前好吧其实已经挺久了Perl 和 Python 还不是大多数 Unix 系统的标准组件。这就意味着用户根本无法确定这两个程序的安装路径——可能在/bin/usr/bin还是/opt/bin谁也说不准。而使用#!/usr/bin/env perl写法就不用纠结这个问题了。And Now Why You Shouldn’t Use#! /usr/bin/env bash不推荐使用#!/usr/bin/env bash的理由When the path is hardcoded in the shebang, I have to run with that interpreter. Thus,#! /bin/bashforces me to use the default installed version of bash. Since bash features are very stable (try running a 2.x version of a Python script under Python 3.x) it’s very unlikely that my particular BASH script will not work, and since my bash script is probably used by this system and other systems, using a non-standard version of bash may have undesired effects. It is very likely I want to make sure that the stable standard version of bash is used with my shell script. Thus, I probably want to hard code the path in my shebang.当 Shebang 中硬编码了解释器路径时脚本就只能使用该路径下的解释器运行。因此#!/bin/bash写法会强制脚本使用系统默认安装的 bash 版本。由于 bash 的功能特性非常稳定这一点和 Python 不同——你试试在 Python 3.x 环境下运行 Python 2.x 脚本就知道了因此我编写的 bash 脚本几乎不会出现兼容性问题。而且由于我的 bash 脚本可能会在本机和其他系统上运行使用非标准版本的 bash 可能会导致一些意外情况。因此为了确保脚本使用稳定的标准版本 bash我更倾向于在 Shebang 中硬编码路径。edited Jul 16, 2015 at 21:35answered Feb 6, 2014 at 21:37David W.Why is it better to use “#!/usr/bin/env NAME” instead of “#!/path/to/NAME” as my shebang?为什么优先使用#!/usr/bin/env NAME而非#!/path/to/NAME作为 ShebangI notice that some scripts which I have acquired from others have the shebang#!/path/to/NAMEwhile others (using the same tool, NAME) have the shebang#!/usr/bin/env NAME.我注意到我从别处获取的脚本中有些使用的 Shebang 是#!/path/to/NAME而另一些使用相同工具NAME的脚本Shebang 却写成#!/usr/bin/env NAME。Both seem to work properly. In tutorials (on Python, for example), there seems to be a suggestion that the latter shebang is better. But, I don’t quite understand why this is so.这两种写法似乎都能正常工作。但在一些教程中例如 Python 教程似乎更推荐使用后一种 Shebang 写法。我不太理解其中的原因。I realize that, in order to use the latter shebang, NAME must be in the PATH whereas the first shebang does not have this restriction.我明白使用后一种写法的前提是NAME必须在PATH环境变量中而前一种写法则没有这个限制。Also, it appears (to me) that the first would be the better shebang, since it specifies precisely where NAME is located. So, in this case, if there are multiple versions of NAME (e.g., /usr/bin/NAME, /usr/local/bin/NAME), the first case specifies which to use.而且在我看来前一种写法似乎更优因为它明确指定了NAME程序的位置。这样一来如果系统中存在多个版本的NAME例如/usr/bin/NAME和/usr/local/bin/NAME前一种写法可以精确指定要使用的版本。My question is why is the first shebang preferred to the second one?我的问题是为什么第二种 Shebang 写法反而比第一种更受推崇edited Jul 16, 2015 at 0:23Eric Renoufasked Jan 21, 2012 at 1:06TheGeeko61TheGeeko61: In my case I had something broken and some variables wasn’t in env. So I suggest to use this shebang to verify if env is correctly loaded.TheGeeko61我之前遇到过一个问题程序运行异常部分变量没有出现在环境变量中。因此我建议可以用这种 Shebang 写法来验证环境变量是否被正确加载。– CybercartelCommentedJan 21, 2012 at 10:52AnswersIt isn’t necessarily better.这种写法并非绝对更优。The advantage of#!/usr/bin/env pythonis that it will use whateverpythonexecutable appears first in the user’s$PATH.#!/usr/bin/env python的优势在于它会使用用户$PATH环境变量中最先出现的python可执行文件。Thedisadvantageof#!/usr/bin/env pythonis that it will use whateverpythonexecutable appears first in the user’s$PATH.而#!/usr/bin/env python的劣势也正在于此它会使用用户$PATH环境变量中最先出现的python可执行文件。That means that the script could behave differently depending on who runs it. For one user, it might use the/usr/bin/pythonthat was installed with the OS. For another, it might use an experimental/home/phred/bin/pythonthat doesn’t quite work correctly.这意味着脚本的运行行为可能会因执行用户的不同而产生差异。对于某一个用户来说脚本可能调用系统预装的/usr/bin/python而对于另一个用户来说脚本可能调用一个尚在测试中的/home/phred/bin/python这个版本的 Python 可能存在功能缺陷。And ifpythonis only installed in/usr/local/bin, a user who doesn’t have/usr/local/binin$PATHwon’t even be able to run the script. (That’s probably not too likely on modern systems, but it could easily happen for a more obscure interpreter.)此外如果python仅安装在/usr/local/bin目录下那么没有将该目录加入$PATH的用户将无法运行这个脚本。这种情况在现代系统中可能不太常见但对于一些小众的解释器来说这种问题很容易出现。By specifying#!/usr/bin/pythonyou specify exactly which interpreter will be used to run the scripton a particular system.通过写成#!/usr/bin/python你可以精确指定某一特定系统上运行脚本时要使用的解释器。Another potential problem is that on many systems, the#!/usr/bin/envtrick doesn’t let you pass arguments to the intrepreter (other than the name of the script, which is passed implicitly). Thisusuallyisn’t an issue, but it can be. Many Perl scripts are written with#!/usr/bin/perl -w, butuse warnings;is the recommended replacement these days. Csh scripts should use#!/bin/csh -f– but csh scripts are not recommended in the first place. But there could be other examples.另一个潜在问题是在许多系统中#!/usr/bin/env这种写法无法向解释器传递参数脚本名称除外它会被隐式传递。这一问题通常不会造成影响但在某些场景下可能引发异常。许多 Perl 脚本会写成#!/usr/bin/perl -w不过如今更推荐使用use warnings;语句来替代-w参数。Csh 脚本则应该写成#!/bin/csh -f——但首先需要说明的是并不推荐使用 Csh 编写脚本。当然类似的例子还有很多。UPDATE: theenvof FreeBSD has a-Soption (copied by GNU coreutilsenvin 8.30 with a--split-stringalias) that allows passing multiple arguments, so for example#!/usr/bin/env csh -fwill fail on systems whose shebang accepts only one argument after the interpreter, but#!/usr/bin/env -S csh -fwill work on those such as Linux where what’s after the interpreter is bundled into one argument. Manyenvimplementations such asNetBSD’s,busybox,toyboxstill don’t support it so that won’t help you write portable scripts.更新说明FreeBSD 系统的env命令提供了-S选项GNU coreutils 工具集中的env命令从 8.30 版本开始借鉴了该功能并提供--split-string作为别名该选项允许向解释器传递多个参数。例如#!/usr/bin/env csh -f在仅支持传递一个参数的系统上会执行失败而#!/usr/bin/env -S csh -f在 Linux 等将解释器后的内容视为单个参数的系统上则可以正常运行。但需要注意的是许多env命令的实现版本例如 NetBSD、busybox、toybox 中的env尚不支持-S选项因此这种写法并不能保证脚本的可移植性。I have a number of Perl scripts in a personal source control system that I install when I set up an account on a new system. I use an installer script that modifies the#!line of each script as it installs it in my$HOME/bin. (I haven’t had to use anything other than#!/usr/bin/perllately; it goes back to times when Perl often wasn’t installed by default.)我在个人代码版本控制系统中存储了一些 Perl 脚本当我在新系统上创建账号时会安装这些脚本。我编写了一个安装脚本在将这些脚本安装到$HOME/bin目录时自动修改每个脚本的#!行内容。我最近已经不再需要使用#!/usr/bin/perl之外的写法了这种兼容写法源于 Perl 尚未成为系统默认安装组件的年代。A minor point: the#!/usr/bin/envtrick is arguably an abuse of theenvcommand, which was originally intended (as the name implies) to invoke a command with an altered environment. Furthermore, some older systems (including SunOS 4, if I recall correctly) didn’t have theenvcommand in/usr/bin. Neither of these is likely to be a significant concern.envdoes work this way, a lot of scripts do use the#!/usr/bin/envtrick, and OS providers aren’t likely to do anything to break it. Itmightbe an issue if you want your script to run on a really old system, but then you’re likely to need to modify it anyway.补充一个小细节严格来说#!/usr/bin/env这种写法算是对env命令的一种“滥用”——顾名思义env命令的设计初衷是在修改后的环境中调用指定命令。此外一些老旧系统如果我没记错的话包括 SunOS 4的env命令并不在/usr/bin目录下。不过这两个问题都不太可能引发严重问题。env命令确实支持这种用法大量脚本也都在使用#!/usr/bin/env写法操作系统提供商一般不会做出破坏这种兼容性的改动。如果你希望脚本能在非常老旧的系统上运行这或许会成为一个问题但即便如此你很可能也需要对脚本本身进行其他修改。Another possible issue, (thanks to Sopalajo de Arrierez for pointing it out in comments) is that cron jobs run with a restricted environment. In particular,$PATHis typically something like/usr/bin:/bin. So if the directory containing the interpreter doesn’t happen to be in one of those directories, even if it’s in your default$PATHin a user shell, then the/usr/bin/envtrick isn’t going to work. You can specify the exact path, or you can add a line to your crontab to set$PATH(man 5 crontabfor details).另一个可能存在的问题是感谢 Sopalajo de Arrierez 在评论区指出这一点定时任务cron job会在受限的环境中运行。具体来说定时任务的$PATH环境变量通常只包含/usr/bin:/bin这样的默认目录。因此如果解释器所在的目录不在这些默认目录中即便它在用户 Shell 的默认$PATH里/usr/bin/env这种写法也无法正常工作。你可以直接在 Shebang 中填写解释器的绝对路径或者在定时任务配置文件中添加一行命令来设置$PATH详情可参考man 5 crontab。Kevin’s comment points out that Python’svirtualenvcreates a special case, where the environment installs a Python interpreter in a special directory that’s inserted at the front of$PATH. For that particular environment (and perhaps others like it), the#!/usr/bin/env pythontrick (orpython3?) is likely to be the best solution. (I haven’t used virtualenv myself.)Kevin 在评论中提到Python 的virtualenv工具会构成一种特殊场景该工具会在一个特定目录中安装 Python 解释器并将这个目录添加到$PATH环境变量的最前端。对于这种特定环境以及其他类似环境#!/usr/bin/env python或者写成python3很可能是最佳解决方案。我本人并未使用过 virtualenv。edited Jul 2, 2024 at 6:24Stéphane Chazelasanswered Jan 21, 2012 at 6:45Keith Thompson8If/usr/bin/perlis perl 5.8,$HOME/bin/perlis 5.12, and a script requiring 5.12 hardcodes/usr/bin/perlin the shebangs, it can be a major pain to run the script. I’ve rarely seen having/usr/bin/env perlgrab perl from the PATH be a problem, but it is often very helpful. And it is much prettier than the exec hack!如果/usr/bin/perl是 5.8 版本$HOME/bin/perl是 5.12 版本而一个依赖 5.12 版本的脚本却在 Shebang 中硬编码了/usr/bin/perl那么运行这个脚本会变得非常麻烦。我几乎没遇到过/usr/bin/env perl从PATH中查找 Perl 解释器引发的问题相反这种写法经常能带来便利。而且它比那些通过exec实现的技巧写法要优雅得多– William PursellCommentedJan 25, 2012 at 20:3015It’s worth noting that, if you want to use a specific interpreter version,/usr/bin/envis still better. simply because there usuallyaremultiple interpreter versions installed on your machine named perl5, perl5.12, perl5.10, python3.3, python3.32, etc. and if your app has only been tested on that specific version, you can still specify#!/usr/bin/env perl5.12and be okay even if the user has it installed somewhere unusual. In my experience, ‘python’ is usually just a symlink to the system standard version (not necessarily the most recent version on the system).需要注意的是如果你想使用特定版本的解释器/usr/bin/env写法依然是更优选择。原因很简单你的机器上通常会安装多个版本的解释器它们的名称可能是 perl5、perl5.12、perl5.10、python3.3、python3.32 等。如果你的应用程序只在某个特定版本下经过测试你可以写成#!/usr/bin/env perl5.12这样即使用户将该版本安装在非标准路径下脚本也能正常运行。根据我的经验python这个名称通常只是一个指向系统标准版本的符号链接该版本不一定是系统中最新的版本。– rootCommentedJul 20, 2013 at 19:4411root: For Perl,use v5.12;servessomeof that purpose. And#!/usr/bin/env perl5.12will fail if the system has Perl 5.14 but not 5.12. For Python 2 vs. 3,#!/usr/bin/python2and#!/usr/bin/python3are likely to work.root对于 Perl 语言来说use v5.12;语句可以在一定程度上实现版本控制的目的。但如果系统中安装的是 Perl 5.14 而非 5.12那么#!/usr/bin/env perl5.12这种写法就会失效。对于 Python 2 和 Python 3 的区分写成#!/usr/bin/python2和#!/usr/bin/python3通常是可行的。– Keith ThompsonCommentedJul 20, 2013 at 21:448If it doesn’t work with/usr/bin/perl, I’ll find out very quickly, and it’s the system owner/administrator’s responsibility to keep it up to date. If you want to run my script with your own perl, feel free to grab and modify a copy or invoke it viaperl foo. (And you might consider the possibility that the 55 people who upvoted this answer also know a thing or two. It’s certainly possible that you’re right and they’re all wrong, but that’s not the way I’d bet.)如果脚本在/usr/bin/perl环境下无法运行我会很快发现这个问题而保持解释器版本更新是系统所有者或管理员的责任。如果你希望用自己的 Perl 版本运行我的脚本完全可以复制一份脚本并修改 Shebang或者通过perl foo这种方式调用脚本。你或许可以想想给这个回答点赞的 55 个人大概率也不是外行。当然你有可能是对的而他们都是错的但我并不这么认为。—— Keith Thompson– Keith ThompsonCommentedDec 14, 2013 at 22:038This answer is not congruent with how Python in particular is commonly used. The Python executable you want to use israrely/usr/bin/python. Typically, the one you want lives in a Virtualenv, and is at the front of the user’s$PATH. In the rare situations where that isnotthe case,/usr/binwill usually be on the user’s$PATHanyway.这个回答与 Python 语言的实际常用场景并不相符。在大多数情况下你真正想使用的 Python 可执行文件并不是/usr/bin/python。通常来说目标 Python 解释器位于 虚拟环境Virtualenv 中并且该虚拟环境的目录会被添加到用户$PATH环境变量的最前端。即便在少数不使用虚拟环境的场景下/usr/bin目录通常也会包含在用户的$PATH中。– KevinCommentedDec 26, 2015 at 23:31130Because/usr/bin/envcan interpret your$PATH, which makes scripts more portable.因为/usr/bin/env能够解析你的$PATH环境变量这会让脚本具备更强的可移植性。#!/usr/local/bin/pythonWill only run your script if python is installed in/usr/local/bin.只有当 Python 安装在/usr/local/bin目录下时这个脚本才能正常运行。#!/usr/bin/env pythonWill interpret your$PATH, and find python in any directory in your$PATH.这种写法会解析你的$PATH环境变量在$PATH包含的任意目录中查找 Python 解释器。So your script is more portable, and will work without modification on systems where python is installed as/usr/bin/python, or/usr/local/bin/python, or even custom directories (that have been added to$PATH), like/opt/local/bin/python.因此你的脚本会具备更强的可移植性无需修改即可在不同系统上运行——无论 Python 被安装在/usr/bin/python、/usr/local/bin/python还是/opt/local/bin/python这类自定义目录已添加到$PATH中。Portability is the only reason usingenvis preferred to hard coded paths.相比于硬编码路径使用env写法更受推崇的唯一原因就是可移植性。answered Jan 21, 2012 at 1:35Tim Kennedy31Custom directories forpythonexecutables are particularly common asvirtualenvusage increases.随着virtualenv工具使用越来越广泛将 Python 可执行文件放在自定义目录的场景也变得尤为常见。– Xiong ChiamiovCommentedNov 22, 2013 at 0:012What about#! python, why isn’t that used?那#! python这种写法呢为什么没人用– kristianpCommentedMay 14, 2018 at 23:5411#! pythonisn’t used because you’d have to be in the same directory as the python binary, since the barewordpythonis interpreted as the complete path to the file. If you don’t have a python binary in the current directory, you’ll get an error likebash: ./script.py: python: bad interpreter: No such file or directory. It’s the same as if you used#! /not/a/real/path/python没人用#! python这种写法是因为系统会将单独的python这个词解析为程序的完整路径这就意味着你必须在 Python 可执行文件所在的目录下才能运行脚本。如果当前目录中没有 Python 可执行文件你会收到类似bash: ./script.py: python: bad interpreter: No such file or directory的错误提示。这种写法的效果和#! /not/a/real/path/python是一样的。– Tim KennedyCommentedMay 16, 2018 at 16:142TimKennedyuname -asays: Linux silvius 5.6.0-2-amd64 #1 SMP Debian 5.6.14-1 (2020-05-23) x86_64 GNU/Linux, and I’m using zsh. zsh is the key: I have the same failure when running from bash, or withperl -e exec /tmp/foo or die $!. TIL, zsh is doing way more work than it has to.TimKennedy 我的系统信息是Linux silvius 5.6.0-2-amd64 #1 SMP Debian 5.6.14-1 (2020-05-23) x86_64 GNU/Linux我使用的 Shell 是 zsh。问题的关键就在于 zsh如果我在 bash 中运行脚本或者通过perl -e exec /tmp/foo or die $!这种方式调用都会遇到同样的错误。今天我才发现zsh 竟然做了这么多本没必要的工作。– Jonathan Klabunde TomerCommentedJun 1, 2020 at 7:152TimKennedy aha, fromman zsh-misc: If execution fails because the file is not in executable format, and the file is not a directory, it is assumed to be a shell script. /bin/sh is spawned to execute it. If the program is a file beginning with#!, the remainder of the first line specifies an interpreter for the program. The shell will execute the specified interpreter on operating systems that do not handle this executable format in the kernel. So zsh has implemented its own shebang-line parsing in case it runs on a non-POSIX system, and its implementation differs from Linux kernels. TimKennedy 啊我在man zsh-misc中找到了答案“如果文件执行失败且原因是文件格式不可执行、同时该文件不是目录则系统会将其视为 Shell 脚本并启动/bin/sh来执行它。如果该文件以#! 开头则首行的剩余部分会指定该程序的解释器。在内核不支持这种可执行文件格式的操作系统上Shell 会自行执行指定的解释器。” 所以 zsh 实现了一套自己的 Shebang 行解析逻辑以兼容非 POSIX 标准的系统而这套逻辑和 Linux 内核的解析逻辑并不相同。– Jonathan Klabunde TomerCommentedJun 1, 2020 at 7:3080Objective Criteria/Requirements:客观判定标准与需求In determining whether to use anabsoluteorlogical(/usr/bin/env) path to an interpreter in a shebang, there are two key considerations:在决定 Shebang 中使用解释器的绝对路径还是逻辑路径即/usr/bin/env写法时需要重点考虑两个核心因素a)Theinterpretercan be found on the target system目标系统上能够找到对应的解释器b)Thecorrect versionof theinterpretercan be found on the target system目标系统上能够找到对应解释器的正确版本If weAGREEthat “b)” is desirable,we also agree that:如果我们认同“b) 找到正确版本的解释器”这一需求的重要性那么我们也应当认同c) It’s preferable our scriptsfailrather than execute using an incorrect interpreter version and potentially achieve inconsistent results.与其让脚本在错误的解释器版本下运行并产生不一致的结果不如让脚本直接执行失败。If weDON’T AGREEthat “b)” matters, then any interpreter found will suffice.如果我们不认同“b) 找到正确版本的解释器”这一需求的重要性那么只要能找到任意版本的解释器就足够了。Testing:测试过程Since using alogicalpath —/usr/bin/envto the interpreter in the shebang — is the most extensible solution allowing the same script to execute successfully on target hosts with different paths to the same interpreter, we’ll test it — using Python, due to its popularity — to determine whether it meets our criteria.由于在 Shebang 中使用解释器的逻辑路径即/usr/bin/env写法是扩展性最强的方案——它可以让同一个脚本在安装路径不同的目标主机上成功运行——因此我们将以使用广泛的 Python 为例测试这种写法是否满足上述判定标准。Does/usr/bin/envlive in a predictable, consistent location onPOPULAR(not “every”) operating systems?Yes:在主流并非所有操作系统中/usr/bin/env是否位于一个可预测、统一的路径下答案是肯定的RHEL 7.5Ubuntu 18.04Raspbian 10 (“Buster”)OSX 10.15.02Below Python script executed both inside and outside of virtual envelopes (Pipenvused) during tests:测试过程中以下 Python 脚本分别在虚拟环境使用 Pipenv 工具内和虚拟环境外执行#!/usr/bin/env pythonX.x import sys print(sys.version) print(Hello, world!)The shebang in the script was varied by the Python version number desired (all installed on the same host):我们修改脚本 Shebang 中的 Python 版本号所有版本均已安装在同一台主机上进行多组测试#!/usr/bin/env python2#!/usr/bin/env python2.7#!/usr/bin/env python3#!/usr/bin/env python3.5#!/usr/bin/env python3.6#!/usr/bin/env python3.7Expected results: thatprint(sys.version)env python*X*.*x*. Each time./test1.pywas executed using a different installed Python version, the correct version specified in the shebang was printed.预期结果print(sys.version)语句输出的版本号应当与env python*X*.*x*命令调用的 Python 版本号一致。测试结果显示每次使用不同版本的 Python 执行./test1.py脚本时终端都会打印出 Shebang 中指定的正确版本号。Testing Notes:测试说明Tests were exclusively limited to Python测试范围仅限于 Python 语言Perl, like Python,MUSTlive in/usr/binaccording to the FHS按照文件系统层次结构标准FHS的要求Perl 和 Python 一样必须安装在/usr/bin目录下I’ve not tested every possible combination on every possible number of Linuxy/Unixy Operating System and version of each Operating System.我并未在所有类 Linux / 类 Unix 操作系统及其不同版本中测试所有可能的组合。Conclusion:结论Although it’s TRUE that#!/usr/bin/env pythonwill use the first version of Python it matches in the user’s Path, we can enforce an express preference by specifying a version number such as#!/usr/bin/env python*X*.*x*. Indeed, developers don’t care which interpreter is found “first”; all they care about is that their code is executed using the specified interpreter they know to be compatible with their code to ensure consistent results —wherever that may live in the filesystem…诚然#!/usr/bin/env python写法会使用用户Path环境变量中最先匹配到的 Python 版本但我们可以通过指定版本号例如#!/usr/bin/env python*X*.*x*来强制使用特定版本。事实上开发者并不关心哪个解释器会被“最先”找到他们真正关心的是代码能够在已知兼容的指定解释器版本下运行从而确保结果的一致性——无论该解释器位于文件系统的哪个位置。In terms of portability/flexibility, using alogical—/usr/bin/env— rather thanabsolutepath not only meets requirements a), b) c) from my testing with different versions ofPython, but also has the benefit of fuzzy-logic finding the same version interpreter even if they live at different paths on different Operating Systems. And althoughMOSTdistros respect the FHS, not all do.从可移植性与灵活性的角度来看使用/usr/bin/env这种逻辑路径而非绝对路径的写法不仅在我针对不同 Python 版本的测试中满足了 a)、b)、c) 三项需求还具备一个优势即便同一版本的解释器在不同操作系统中位于不同路径这种写法也能通过模糊匹配找到目标解释器。尽管大多数发行版都遵循文件系统层次结构标准但并非所有发行版都严格遵守该标准参考链接 https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard#FHS_compliance。So, where a script willFAILif the binary lives in a differentabsolutepath than specified in the shebang, the same script using alogicalpathSUCCEEDSas it keeps going until it finds a match, thereby offering greater reliability extensibility across platforms.因此当可执行文件的实际路径与 Shebang 中硬编码的绝对路径不一致时脚本会执行失败而使用逻辑路径的同一脚本则会执行成功——它会持续在PATH中查找直到找到匹配的解释器。这种写法因此具备更强的跨平台可靠性与扩展性。edited Mar 13, 2024 at 23:52G-Man Says ‘Reinstate Monica’answered Feb 6, 2020 at 1:04F1Linux8Excellent analysis. We appreciate it.分析得非常透彻感谢分享。– TheGeeko61CommentedFeb 20, 2020 at 23:554The question wasn’t specific to Python. I don’t think you can safely assume that other interpreters will be installed as, for exampleinterpXandinterpX.x. For example, the system I’m using at the moment hasperl,perl5.26.3, andperl5.30.1. Another hasperlandperl5.26.1. Neither has aperl5command. Also, you didn’t mention where thepythonXandpythonX.xinterpreters on any of the systems you tested were installed. If they were all in/usr/binthen your experiment doesn’t demonstrate any advantage of#!/usr/bin/env pythonX.xover#!/usr/bin/pythonX.x.这个问题并非专门针对 Python 语言。我认为不能想当然地认为其他解释器也会同时存在interpX和interpX.x这样的命名版本。例如我目前使用的系统中安装了perl、perl5.26.3和perl5.30.1另一台系统则安装了perl和perl5.26.1。这两台系统都没有perl5这个命令。此外你并没有说明测试中使用的pythonX和pythonX.x解释器安装在哪个目录。如果它们都位于/usr/bin那么你的实验并不能证明#!/usr/bin/env pythonX.x写法比#!/usr/bin/pythonX.x更具优势。– Keith ThompsonCommentedFeb 21, 2020 at 2:553Note that not every Linux system complies to the FHS, not by a long shot. And, paraphrasing the old saying, “Not all the world is Linux”. Many Unix(y) systems have Python, Perl, even bash or tcsh as “optional, unsupported third party additions”, presumably under/usr/localor/opt/*packagename*or some really exotic placements.需要注意的是并非所有 Linux 系统都遵守文件系统层次结构标准差距还很大。而且套用一句老话“并非全世界都是 Linux”。许多类 Unix 系统会将 Python、Perl甚至 bash 或 tcsh 当作“可选的、不受官方支持的第三方组件”这些程序的安装路径很可能是/usr/local、/opt/*packagename*或者一些非常特殊的目录。– vonbrandCommentedFeb 23, 2020 at 4:016UP VOTEDfor theformatting*alone, never mind theveryusefulanswer.单看这份排版就值得点赞*更不用说内容还这么实用。– Teemu LeistiCommentedAug 26, 2020 at 13:301TeemuLeisti I try to save other technologists the effort of solving the same problems I bump into. So it’s nice to hear somebody found my solution useful, especially when it’s involved a fair amount of testing documentation such as this one has. Most obliged for your kind words!TeemuLeisti 我只是想帮其他技术从业者省去解决我遇到过的相同问题的麻烦。因此听到有人觉得我的方案有用我感到非常开心——尤其是这个方案还包含了大量的测试和文档整理工作。非常感谢你的认可– F1LinuxCommentedAug 26, 2020 at 18:2258Specifying the absolute path is more precise on a given system. The downside is that it’s too precise. Suppose you realize that the system installation of Perl is too old for your scripts and you want to use your own instead: then you have to edit the scripts and change#!/usr/bin/perlto#!/home/myname/bin/perl. Worse, if you have Perl in/usr/binon some machines,/usr/local/binon others, and/home/myname/bin/perlon yet other machines, then you’d have to maintain three separate copies of the scripts and execute the appropriate one on each machine.在特定系统上指定绝对路径的写法更加精确。但这种写法的缺点也在于它过于精确。假设你发现系统预装的 Perl 版本太旧无法满足脚本运行需求想要使用自己安装的版本那么你就必须编辑脚本将#!/usr/bin/perl修改为#!/home/myname/bin/perl。更糟糕的是如果有些机器的 Perl 在/usr/bin有些在/usr/local/bin还有些在/home/myname/bin/perl那么你就不得不维护三个不同版本的脚本并在对应的机器上执行相应版本的脚本。#!/usr/bin/envbreaks ifPATHis bad, but so does almost anything. Attempting to operate with a badPATHis very rarely useful, and indicates that you know very little about the system the script is running on, so you can’t rely on any absolute path anyway.如果PATH环境变量配置有误#!/usr/bin/env写法会失效但几乎所有依赖PATH的操作都会受到影响。在PATH配置错误的环境中运行程序这种情况本身就很少见而且这也说明你对脚本运行的目标系统了解甚少因此你根本无法依赖任何绝对路径。There are two programs whose location you can rely on on almost every unix variant:/bin/shand/usr/bin/env. Some obscure and mostly retired Unix variants had/bin/envwithout having/usr/bin/env, but you’re unlikely to encounter them. Modern systems have/usr/bin/envprecisely because of its widespread use in shebangs./usr/bin/envis something you can count on.在几乎所有 Unix 变体系统中有两个程序的路径是可以信赖的/bin/sh和/usr/bin/env。部分小众且基本已淘汰的 Unix 变体系统其env程序位于/bin/env而非/usr/bin/env但你几乎不会遇到这类系统。现代系统之所以将env程序放置在/usr/bin/env正是因为它在 Shebang 中的广泛应用。/usr/bin/env是一个可以放心使用的路径。Apart from/bin/sh, the only time you should use an absolute path in a shebang is when your script isn’t meant to be portable, so you can count on a known location for the interpreter. For example, a bash script that only works on Linux can safely use#!/bin/bash. A script that is only meant to be used in-house can rely on house interpreter location conventions.除了/bin/sh之外唯一适合在 Shebang 中使用绝对路径的场景是你的脚本不需要具备可移植性且你明确知道解释器的固定路径。例如一个仅在 Linux 系统中运行的 bash 脚本可以安全地使用#!/bin/bash写法。一个仅供内部使用的脚本则可以遵循内部约定的解释器路径来编写 Shebang。#!/usr/bin/envdoes have downsides. It’s more flexible than specifying an absolute path but still requires knowing the interpreter name. Occasionally you might want to run an interpreter that isn’t in the$PATH, for example in a location relative to the script. In such cases, you can often make a polyglot script that can be interpreted both by the standard shell and by your desired interpreter. For example, to make a Python 2 script portable both to systems wherepythonis Python 3 andpython2is Python 2, and to systems wherepythonis Python 2 andpython2doesn’t exist:#!/usr/bin/env写法确实存在不足之处。它虽然比硬编码绝对路径更灵活但仍需要你知晓解释器的名称。在某些情况下你可能需要调用不在$PATH中的解释器例如解释器位于脚本的相对路径下。这种场景下你通常可以编写一个多语言兼容脚本让脚本既能被标准 Shell 解析又能被目标解释器执行。例如要让一个 Python 2 脚本同时兼容两种系统——一种系统的python指向 Python 3、python2指向 Python 2另一种系统的python指向 Python 2、且没有python2命令——可以这样编写脚本#!/bin/sh : if type python2 /dev/null 2/dev/null; then exec python2 $0 $ else exec python $0 $ fi # real Python script starts here def …edited Apr 13, 2017 at 12:37CommunityBotanswered May 29, 2013 at 23:38Gilles ‘SO- stop being evil’29Specifically for perl, using#!/usr/bin/envis a bad idea for two reasons.对于 Perl 脚本而言使用#!/usr/bin/env写法并非明智之选原因有两点。First, it’s not portable. On some obscure platforms env isn’t in /usr/bin. Second, as Keith Thompson has noted, it can cause trouble with passing arguments on the shebang line. The maximally portable solution is this:第一这种写法不具备可移植性。在部分小众平台上env程序并不在/usr/bin目录下。第二正如 Keith Thompson 所指出的这种写法在 Shebang 行传递参数时可能会出现问题。兼容性最佳的解决方案如下#!/bin/sh exec perl -x $0 $ #!perlFor details on how it works, see ‘perldoc perlrun’ and what it says about the -x argument.关于该写法的工作原理可参考 perldoc perlrun 文档中对-x参数的说明。edited Aug 11, 2018 at 16:44Maximilian Heinzleranswered May 2, 2013 at 15:19DrHyde1Exactly the answer I was looking for: how to write portable “shebang” for perl script that will allow additional arguments passed to perl (last line in your example accepts additional arguments).这正是我要找的答案如何为 Perl 脚本编写可移植的 Shebang并且支持向 Perl 解释器传递额外参数你示例中的最后一行就支持接收额外参数。– AmokHuginnssonCommentedMay 25, 2015 at 21:23AmokHuginnsson it is a bletcherous kludge.AmokHuginnsson 这确实是一种蹩脚的权宜之计。– vonbrandCommentedFeb 23, 2020 at 4:072It is, but it’s a bletcherous kludge thatworks. It’s a blethcherous kludge thatexistsbecause less kludgey solutions don’t work.确实如此但这种蹩脚的方案切实有效。正因为更优的方案无法实现才诞生了这种权宜之计。– DrHydeCommentedFeb 24, 2020 at 21:59What ifshis not in/bin? True story for google distroless containers.如果sh程序不在/bin目录下该怎么办谷歌的 distroless 容器就存在这种情况。– LLlAMnYPCommentedJul 28, 2020 at 16:172Yeah, it also won’t work if perl isn’t in the path, or on an Amiga, or … If you’re using something weird like that then you’re going to have to do some work yourself.没错如果 Perl 解释器不在PATH中或者在 Amiga 这类系统上这个方案同样无法运行。如果你使用的是这类特殊环境就需要自行定制解决方案了。– DrHydeCommentedJul 29, 2020 at 11:1020The reason there is a distinction between the two is because of how scripts are executed.这两种 Shebang 写法存在差异的根本原因在于脚本的执行机制不同。Using/usr/bin/env(which, as mentioned in other answers, is not in/usr/binon some OSes) is required because you can’t just put an executable name after the#!- it must be an absolute path. This is because the#!mechanism works on a lower level than the shell. It’s part of the kernel’s binary loader. This can be tested. Put this in a file and mark it executable:必须使用/usr/bin/env写法正如其他回答所提及的部分操作系统的env程序不在/usr/bin目录下的原因是你不能在#!后直接填写可执行文件名称必须填写绝对路径。这是因为#!机制的工作层级低于 Shell它属于内核二进制加载器的一部分。你可以通过以下方式验证这一点将以下内容写入文件并标记为可执行#!bash echo fooYou will find it prints an error like this when you attempt to run it:当你尝试运行该文件时会收到如下错误提示Failed to execute process ./test.sh. Reason: The file ./test.sh does not exist or could not be executed.If a file is marked executable and begins with a#!, the kernel (which does not know about$PATHor the current directory: these are user-land concepts) will look for a file using an absolute path. Because using an absolute path is problematic (as mentioned in other answers), someone came up with a trick: You can run/usr/bin/env(which is almost always in that location) to run something using$PATH.如果一个文件被标记为可执行且以#!开头内核内核并不识别$PATH或当前目录这类用户态概念会按照绝对路径去查找对应的程序。由于使用绝对路径存在诸多问题正如其他回答所提及的有人想到了一个技巧可以运行/usr/bin/env这个路径几乎在所有系统中都稳定存在借助它来通过$PATH查找并运行目标程序。answered Jan 19, 2015 at 2:54Tiffany Bennett17There are two more problems with using#!/usr/bin/env使用#!/usr/bin/env写法还存在另外两个问题。It doesn’t solve the problem of specifying the full path to the interpreter, it just moves it toenv.这种写法并没有解决“指定解释器完整路径”这一核心问题只是将路径依赖转移到了env程序上。envis no more guaranteed to be in/usr/bin/envthanbashis guaranteed to be in/bin/bashor python in/usr/bin/python.env程序并不一定就位于/usr/bin/env这一点和bash不一定在/bin/bash、Python 不一定在/usr/bin/python是同一个道理。envoverwrites ARGV[0] with the name of the interpreter (e.g. bash or python).env程序会将ARGV[0]的值替换为解释器的名称例如bash或python。This prevents your script’s name from appearing in, e.g.,psoutput (or changes how/where it appears) and makes it impossible to find it with, e.g,ps -C scriptname.sh这会导致你的脚本名称无法出现在ps等命令的输出结果中或者改变其显示方式和位置进而无法通过ps -C scriptname.sh这类命令查询到脚本进程。[update 2016-06-04]And a third problem:此外还有第三个问题Changing your PATH ismorework than just editing the first line of a script, especially when scripting such edits is trivial. e.g:修改PATH环境变量比直接编辑脚本首行要繁琐得多尤其是编写脚本修改首行的操作非常简单。例如printf %s\n 1 i #!$(type -P python2) . w | ed foo.pyAppending or pre-pending a directory to$PATHis fairly easy (although you still have to edit a file to make it permanent - your~/.profileor whatever - and it’s far from easy to script THAT edit because the PATH could be set anywhere in the script, not in the first line).向$PATH中追加或前置一个目录相对简单但要让这个修改永久生效你仍然需要编辑配置文件例如~/.profile等。而编写脚本完成这个配置文件的修改操作却并不容易因为PATH的定义可能出现在配置文件的任意位置并非固定在首行。Changing the order of PATH directories is significantly more difficult…and far harder than just editing the#!line.调整PATH中目录的顺序则要困难得多远比直接修改#!行要复杂。And you still have all the other problems that using#!/usr/bin/envgives you.而且你仍然会面临使用#!/usr/bin/env写法带来的其他所有问题。jlliagre suggests in a comment that#!/usr/bin/envis useful for testing your script with multiple interpreter versions, “by only changing their PATH / PATH order”jlliagre 在评论中提出#!/usr/bin/env写法有助于测试脚本在多个解释器版本下的运行情况只需“修改PATH环境变量或调整其目录顺序”即可。If you need to do that, it’s much easier to just have several#!lines at the top of your script (they’re just comments anywhere but the very first line) and cut/copy-and-paste the one you want to use now to the first line.如果你确实需要这样做更简单的方法是在脚本顶部写入多个#!行除了首行之外其他位置的#!行都会被视为注释然后将当前需要使用的那一行剪切或复制到首行即可。Invi, that would be as simple as moving the cursor to the#!line you want, then typingdd1GPorY1GP. Even with an editor as trivial asnano, it would take seconds to use the mouse to copy and paste.在vi编辑器中操作非常简单将光标移动到目标#!行输入dd1GP或Y1GP命令即可。即便是使用nano这类简易编辑器用鼠标复制粘贴也只需要几秒钟。Overall, the advantages of using#!/usr/bin/envare minimal at best, and certainly don’t even come close to outweighing the disadvantages. Even the “convenience” advantage is largely illusory.总而言之使用#!/usr/bin/env写法的优势微乎其微完全不足以抵消其带来的弊端。甚至连它所谓的“便捷性”优势在很大程度上也只是一种错觉。IMO, it’s a silly idea promoted by a particular kind of programmer who thinks that operating systems are not something to be worked with, they are aproblemto be worked around (or ignored at best).在我看来这种写法是一类程序员鼓吹的不明智方案。这类程序员认为操作系统不是需要协同工作的工具而是需要去规避的麻烦或者说最好能忽略它的存在。PS: here’s a simple script to change the interpreter of multiple files at once.附以下是一个可以批量修改多个脚本解释器路径的简单脚本。change-shebang.sh:#!/bin/bash interpreter$1 shift if [ -z $(type -P $interpreter) ] ; then echo Error: $interpreter is not executable. 2 exit 1 fi if [ ! -d $interpreter ] [ -x $interpreter ] ; then shebang#!$(realpath -e $interpreter) || exit 1 else shebang#!$(type -P $interpreter) fi for f in $ ; do printf %s\n 1 i $shebang . w | ed $f doneRun it as, e.g.,change-shebang.sh python2.7 *.pyorchange-shebang.sh $HOME/bin/my-experimental-ruby *.rb你可以这样运行该脚本change-shebang.sh python2.7 *.py或者change-shebang.sh $HOME/bin/my-experimental-ruby *.rbedited Jun 4, 2016 at 3:17answered Oct 25, 2015 at 6:18cas6Nobody else here has mentioned the ARGV[0] problem. And nobody has mentioned the /path/to/env issue in a form that directly addresses one of the arguments for using it (i.e. that bash or perl might be in an unexpected location).目前为止还没有人提到ARGV[0]的问题。也没有人以直接回应“bash或perl可能位于非预期路径”这一支持理由的方式指出env程序自身路径的问题。– casCommentedOct 25, 2015 at 7:553The interpreter path issue is easily fixed by a sysadmin with symlinks, or by the user editing their script. It’s certainly not a significant enough problem to encourage people to put up with the all of the other issues caused by using env on the shebang line that are mentioned here and on other questions. That’s promoting a bad solution in the same kind of way that encouragingcshscripting is promoting a bad solution: it kind of works but there are much better alternatives.解释器路径的问题很容易解决系统管理员可以通过创建符号链接来处理用户也可以直接编辑脚本。这个问题显然没有严重到需要让人们忍受在 Shebang 中使用env所带来的其他所有问题——这些问题在本文和其他相关问答中都有提及。这种做法就像推荐使用csh编写脚本一样都是在鼓吹一种糟糕的方案它虽然勉强能用但存在好得多的替代方案。– casCommentedOct 25, 2015 at 8:372Not everybody is a sysadmin on their machine. Theenvsolution is aimed at helping non operating system specialists to copy/paste or download scripts that have a good chance to work as is. It is also one of the methods that allow more advanced users to experiment with multiple unchanged scripts to be executed by custom versions of the target interpreter by only changing their PATH / PATH order (sorry about that too long sentence…)并非所有人都是自己机器的系统管理员。env方案的目的是帮助非操作系统专业人士让他们复制粘贴或下载的脚本有很大概率可以直接运行。同时对于高级用户而言这也是一种可以实现在不修改脚本的前提下通过调整PATH环境变量或其目录顺序来测试脚本在不同自定义解释器版本下运行情况的方法抱歉这句话有点太长了……。– jlliagreCommentedOct 25, 2015 at 10:383non-sysadmins can ask their sysadmin to do it. or they can simply edit the script and change the#!line.非系统管理员可以请系统管理员帮忙解决或者自己直接编辑脚本修改#!行即可。– casCommentedOct 25, 2015 at 10:516That is precisely what env is helping to avoid: depending on a sysadmin or OS specific technical knowledge unrelated to python or whatever.这正是env方案想要避免的情况避免依赖系统管理员避免需要掌握与 Python 等编程语言无关的、特定于操作系统的技术知识。– jlliagreCommentedOct 25, 2015 at 17:2712Adding another example here:这里再补充一个例子Usingenvis also useful when you want to share scripts between multiplervmenvironments for example.例如当你需要在多个rvm环境之间共享脚本时使用env写法会非常方便。Running this on the cmd line, shows which ruby version will be used when#!/usr/bin/env rubyis used inside a script:在命令行中运行以下命令可以查看当脚本使用#!/usr/bin/env ruby作为 Shebang 时系统会调用哪个版本的 Ruby 解释器env ruby --versionTherefore, when you useenv, you can use different ruby versions through rvm, without changing your scripts.因此当你使用env写法时可以通过rvm工具切换不同的 Ruby 版本而无需修改脚本本身。edited Jan 23, 2012 at 17:54answered Jan 22, 2012 at 21:35Not Now1// , Excellent idea. The whole point of multiple interpreters is NOT to break the code, or to have code depend uponthatspecificinterpreter.这个想法非常好。使用多个解释器版本的核心意义就是为了不破坏代码不让代码依赖于某个特定的解释器版本。– Nathan BasaneseCommentedJan 15, 2016 at 20:52Or maybe you could use different interpreter name if you change the language? If you putenv rubyat the front of your script and youactually require some specific version, you’re doing it backwards. Theenv rubyshould meananyversion of ruby is okay. Both python and ruby have this same problem where the language syntax or features is different but different peoplepretendto use the same language and use identical shebang.或者如果你切换了编程语言是不是应该使用不同的解释器名称如果你在脚本开头写了env ruby但实际上需要某个特定版本的 Ruby那你的写法就是本末倒置了。env ruby这种写法的本意应该是“任意 Ruby 版本均可”。Python 和 Ruby 都存在同样的问题不同版本的语言语法或特性存在差异但人们却试图用相同的 Shebang 来兼容不同版本假装它们是同一种语言。– Mikko RantalainenCommentedApr 14, 2022 at 11:33via:What is the preferred Bash shebang (“#!”)?https://stackoverflow.com/questions/10376206/what-is-the-preferred-bash-shebangBash Reference Manualhttps://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html#Bash-POSIX-Modeshebang - Why is #!/usr/bin/env bash superior to #!/bin/bash?https://stackoverflow.com/questions/21612980/why-is-usr-bin-env-bash-superior-to-bin-bashshell script - Why is it better to use “#!/usr/bin/env NAME” instead of “#!/path/to/NAME” as my shebang?https://unix.stackexchange.com/questions/29608/why-is-it-better-to-use-usr-bin-env-name-instead-of-path-to-name-as-my