Linux check the shell

How do I find out what shell I am using on Linux/Unix?

B oth Linux and Unix provides various shell out of the box. One can find bash (Bourne Again shell), ksh (Korn shell), csh (C shell)/tcsh (TC shell), sh (Bourne shell) and more installed by default. However, how do you check which shell am I using? What is the best way to find out what shell I am using on Linux? The echo $SHELL is not so reliable. This page explains how to find out which shell I am using at a Linux, MacOS, FreeBSD, or Unix-like systems.

How can I find out what shell I am using?

The following echo command or printf command should work:
echo «$SHELL»
OR
printf «My current shell — %s\n» «$SHELL»
Please note that $SHELL is the shell for the current user but not necessarily the shell that is running at the moment. Try the following examples

How do I check which shell am I using?

Here is another old good Unix trick. Use the ps command with -p option. The following command selects the processes whose process ID numbers appear in pid. Use the following command to find out which shell you are in:
ps -p $$
Sample outputs:

So what is a $ argument passed to the -p option? Remember $ returns the PID (process identification number) of the current process, and the current process is your shell. So running a ps on that number displays a process status listing of your shell. In that listing, you will find the name of your shell (look for CMD column).
ps -p $$
Sample outputs:

From my Linux box:
ps -p $$
Sample outputs:

You can store your shell name in a variable as follows :
MYSHELL=`ps -hp $$|awk ‘‘`
Please note those are backquotes, not apostrophes. Or better try out the following if you have a bash shell:
MYSHELL=$(ps -hp $$|awk ‘‘)
Another option is as follows:
echo $0
OR
printf «%s\n» $0
Sample outputs from the above commands:

Fig.01: Linux check which shell am I using

How do I check how many shells are installed on my Linux box?

The /etc/shells is a text file which contains the full pathnames of valid login shells. Type the following [nixmd name=”cat”] to see list how many shells are installed on your Linux or Unix box:
cat /etc/shells

Use /etc/shells file to check how many shells are installed on your system

• No ads and tracking
• In-depth guides for developers and sysadmins at Opensourceflare✨
• Join my Patreon to support independent content creators and start reading latest guides:
  • How to set up Redis sentinel cluster on Ubuntu or Debian Linux
  • How To Set Up SSH Keys With YubiKey as two-factor authentication (U2F/FIDO2)
  • How to set up Mariadb Galera cluster on Ubuntu or Debian Linux
  • A podman tutorial for beginners – part I (run Linux containers without Docker and in daemonless mode)
  • How to protect Linux against rogue USB devices using USBGuard

Join Patreon ➔

Okay, so when I open the Terminal app, which shell is opened by default?

Your default shell is defined in /etc/passwd file. So try the following grep command:

How to check which shell am I using:

Use the following Linux or Unix commands:

1. ps -p $$ – Display your current shell name reliably.
2. echo «$SHELL» – Print the shell for the current user but not necessarily the shell that is running at the movement.
3. echo $0 – Another reliable and simple method to get the current shell interpreter name on Linux or Unix-like systems.
4. readlink /proc/$$/exe – Another option to get the current shell name reliably on Linux operating systems.
5. cat /etc/shells – List pathnames of valid login shells currently installed
6. grep «^$USER» /etc/passwd – Print the default shell name. The default shell runs when you open a terminal window.
7. chsh -s /bin/ksh – Change the shell used from /bin/bash (default) to /bin/ksh for your account

Conclusion

Sometimes things are not easy as they seem, and this page is the perfect example of it. I hope you found the suggestion useful when it comes to checking your current running shell. Bash users can display shell version by typing the following command:
$ bash —version
Here is what I got from my Ubuntu Linux 20.04 LTS desktop:

Источник

4 Ways to Check Which Shell You are Using on Linux

Out of the box, Linux provides a wide variety of shells. There is bash (Bourne Again shell) shell which ships by default in many Linux distributions. We also have sh (Bourne Shell), tcsh (TC shell), csh (C shell), Zsh (Z shell) and ksh (Korn Shell).

Curious to know which shell you are using on your Linux system? In this guide, we explore different ways that you can use to check which shell you are currently using in Linux.

1) Using echo command

The Linux echo command is a built-in command that is used to print the output of a string which is passed as an argument. Additionally, you can use the echo command to check the shell that you are running commands in. To accomplish this, execute:

The output shows that I am using the bash shell. Additionally, you can simply run the command:

To get the PID of the shell that you are currently in, run:

2) Using ps command

Commonly used for listing running processes, the ps command in its basic format sheds light on the shell that you are using. Simply execute the command:

From the first line of the output, we can clearly see the PID of the shell and the last column prints out the type of shell, in this case — bash.

Alternatively, you can run the command:

You can also use ps -p $$ -o args= which output just the shell name.

3) By viewing /etc/passwd file

The grep command can be used to probe the /etc/passwd file that contains attributes of the users such as username, user ID and group ID.

To display the shell used, invoke the command:

At the very last segment, we get to see the bash used, in this case /bin/bash This also gives you a glimpse of which shell is opened first when you first log in to your system.

4) Using lsof command

Ordinarily, the lsof command, short for list of open files, is used to provide a list of open files on your system. However, when used with the -p $$ flag, it gives a pointer to the shell you are in when you look at the first column of the output.

For example, we can clearly see that we are on the bash shell.

How to check the valid login shells

We have seen various ways that you can employ to check the shell that you are currently in. If you want to know the valid shells on your system, check the /etc/shells file, This file will provide you with the full pathnames of valid login shells in your system. Using the cat command, view the file as shown:

Conclusion

In this guide, we have shared simple but nifty ways that you can use to know which shell you are working on. This is important when writing scripts so that you can know how to start off writing the shebang header. We do hope that this tutorial was beneficial. Send us a shout and don’t forget to share this guide on your social platforms.

Источник

Different Ways to Check Which Shell You are Using on Linux

A shell is a program through which users can interact with the Operating System. Linux provides commonly 4 types of Shell The Bourne Shell ( /bin/sh or /sbin/sh ), The C shell ( /bin/csh ), The Korn Shell ( /bin/ksh ), The GNU Bourne-Again Shell ( /bin/bash ). This article is about to Check that which shell we are using. Here, we discuss five ways by which we can check which shell we are using.

1) Using echo command: Basically, the echo command is used to print the input string, but it is also used to print the name of the shell which we are using with the help of the command.

2) Using ps command: ps command stands for “Process Status”. It is used to check the currently running status and their PIDs. If the ps command is run generally in the shell then it simply tells the name of the shell.

2. Shell name using ps

The first column tells the PID and the last column tells the type of shell i.e. bash.

3) By viewing /etc/passwd file: This tells the feature of the user just like it’s name, shell, and ID. This command is used with the grep command.

4) Using lsof command: lsof stands for LIST OF OPEN FILES. This command used when we want the list of open files in our system. By using the specific flag it gives a pointer to the shell and tells us about that which shell are we using and that specific flag is -p $$. The command looks like.

As you can see clearly in the 3rd line it tells us about the shell we are using.

5) Using readlink /proc/$$/exe: The readlink is used to print the file name. So with the help of this, we print the location of the current shell using the /proc/$$/exe. Command can be written as

Источник

Статический анализатор ShellCheck и улучшение качества скриптов в Linux и Unix

Написание shell-скриптов — занятие увлекательное. Скрипты командной строки помогают автоматизировать повседневные дела. Можно создать нечто прекрасное (или какую-нибудь гадость), однако, если уж что-то писать, хорошо бы точно знать, что код получается именно таким, каким он нужен программисту. Скрипт, написанный некачественно, может представлять опасность. Большинство новичков пишут скрипты, копируя фрагменты кода со StackOverflow, находя то, что им нужно, в Google, или пользуясь сайтами с вопросами и ответами по Linux. Такой подход к программированию выливается в некачественный код и в появление ошибок. Вот, например, команда rm , выполнение которой приведёт к катастрофе, так как переменная VAR не определена:

Многие из проблем скриптов можно решить с помощью линтера, такого, как статический анализатор кода ShellCheck, который написан на Haskell. Он помогает искать ошибки в текстах скриптов и выводить отчёты о проведённых проверках. Это позволяет повысить производительность работы и качество кода. Сегодня мы расскажем о том, как установить и использовать ShellCheck в Linux и Unix-подобных операционных системах.

Установка

Самый простой способ локальной установки ShellCheck заключается в использовании применяемого в вашем дистрибутиве менеджера пакетов вроде apt/apt-get/yum и других.

▍Установка ShellCheck в Debian/Ubuntu Linux

Тут понадобится следующая команда apt / apt-get:

Вот пример реакции системы на эту команду:

▍Установка ShellCheck в CentOS/RHEL/Fedora/Oracle Linux

Сначала нужно включить репозиторий EPEL в CentOS/RHEL:

Дальше надо ввести следующую команду yum:

Вот что будет выведено в ответ на эту команду:

Если вы пользуетесь Fedora, выполните следующую команду dnf:

▍Установка ShellCheck в Arch Linux

Введите следующую команду pacman:

▍Установка ShellCheck в Gentoo Linux

Введите такую команду emerge:

▍Установка ShellCheck в OpenSUSE Linux

Введите следующую команду zypper:

▍Установка ShellCheck в macOS Unix

Воспользуйтесь следующей командой port если вы работаете с MacPorts:

Если вы пользуетесь Homebrew в macOS/OS X, введите такую команду brew:

Как пользоваться ShellCheck

Испытаем ShellCheck на скрипте, содержимое которого просмотрим с помощью команды cat:

Теперь проверим скрипт с помощью ShellCheck:

В ответ программа выдаст следующее:

ShellCheck в действии

Утилита ShellCheck предложила внести исправления, касающиеся использования переменных, не заключённых в кавычки, а также сообщила о других проблемах. Исправим ошибки и снова просмотрим текст скрипта следующей командой:

Вот что, в итоге, получилось:

Интеграция ShellCheck в текстовый редактор

Для установки ansible-vim и neomake/neomake , введите в vim следующую команду:

Для использования плагина введите следующую команду, редактируя bash/sh-скрипт:

Вот как выглядят результаты работы плагина в редакторе:

Neomake выводит предупреждения и сообщения об ошибках с помощью ShellCheck

Итоги

Полагаем, ShellCheck — это замечательный инструмент, который позволяет улучшать и исправлять скрипты командной строки Linux. Он способен обнаруживать множество распространённых недоработок и ошибок в их коде. Если вы хотите узнать о SpellCheck больше — вот сайт проекта, а вот — его репозиторий на GitHub.

Уважаемые читатели! Проверяете ли вы свои скрипты чем-то вроде ShellCheck?

Источник

Linux command to check if a shell script is running or not

What is the linux command to find if a process say aa.sh is running or not. ps command does not seem to work and it does not show the shell script names.

9 Answers 9

The simplest and efficient solution is :

Adding to the answers above —

To use in a script, use the following :-

You can also find your running process in

The solutions above are great for interactive use, where you can eyeball the result and weed out false positives that way.

False positives can occur if the executable itself happens to match, or any arguments that are not script names match — the likelihood is greater with scripts that have no filename extensions.

Here’s a more robust solution for scripting, using a shell function:

• Matching is case-sensitive (on macOS, you could add -i to the pgrep call to make it case-insensitive; on Linux, that is not an option.)
• The getscript function also works with full or partial paths that include the filename component; partial paths must not start with / and each component specified must be complete. The «fuller» the path specified, the lower the risk of false positives. Caveat: path matching will only work if the script was invoked with a path — this is generally true for scripts in the $PATH that are invoked directly.
• Even this function cannot rule out all false positives, as paths can have embedded spaces, yet neither ps nor pgrep reflect the original quoting applied to the command line. All the function guarantees is that any match is not the first token (which is the interpreter), and that it occurs as a separate word, optionally preceded by a path.
• Another approach to minimizing the risk of false positives could be to match the executable name (i.e., interpreter, such as bash ) as well — assuming it is known; e.g.

If you’re willing to make further assumptions — such as script-interpreter paths never containing embedded spaces — the regexes could be made more restrictive and thus further reduce the risk of false positives.

Источник