NAME

shell - Creates a temporary interactive shell session in a disposable working directory

SYNOPSIS

shell [-fq] [-d directory] [shell [...]]

shell [-fkqS] [-s directory] [shell [...]]

shell -v

DESCRIPTION

The shell utility creates an interactive shell session with a clean environment and with an empty working directory.

By specifying a specific shell on the command line, a shell other than the user's login shell may be invoked. If a specific shell is not requested, the SHELL environment variable will be used to infer what shell to start.

The basename of the named shell must correspond to a valid login shell and the actual shell that is started will always be taken from the list of valid login shells (by matching the basename of the specified shell, or $SHELL, against the basenames of the allowed login shells). This behaviour may be bypassed by using the -f command line option.

Any operands present after the name of the shell will be passed as is to the shell in question.

If shell (this utility, not the interactive shell process) receives the USR1 signal, the temporary working directory will not be deleted when the shell session terminates (as if -k had been used from the start).

The options are as follows:

-d directory: Use the specified directory rather than a new temporary directory. This directory will not be deleted when the shell session terminates. This option implies the -k option, and overrides any earlier -s option.
-f: Force the execution of the given command, even if it is not a valid login shell on the current system. The command needs to be specified with an absolute path.
-k: Keep the temporary directory around after terminating the shell session.
-q: Be quiet. Don't output informational messages.
-s directory: Pre-populate the temporary directory with the contents of the named “skeleton directory”. This will copy the whole directory structure rooted in the specified directory to the temporary working directory. This option overrides any earlier -d option.
-S: Do not pre-populate the temporary directory with the contents of a “skeleton directory”, even if the -s option was used earlier on the command line or the SHELL_SKEL environment variable is set.
-v: Output version information and immediately terminate.

ENVIRONMENT

shell uses the following environment variables:

SHELL: Used to determine what shell to start if a specific shell is not specified on the command line. If this variable is unset or empty, then /bin/sh will be used instead.
SHELL_SKEL: Directory to automatically pre-populate the temporary working directory with. This environment variable is not used if any of the -d or -s options are used on the command line.
TMPDIR: Directory in which to create the working directory when the -d option is not used. This variable is used by mktemp which will revert to use /tmp if the variable is not set.

shell clears the environment of the interactive shell that it starts, but also sets the following environment variables:

HOME: Set to the working directory where the shell is started.
PATH: Set to the output of “getconf PATH”.
PS1: Set to the string ‘$ ’ (dollar-sign and space). Note that some shells ignore this variable if passed from the parent environment.
SHELL: Set to the absolute path of the real shell executable. This may be different from the shell mentioned on the command line as the actual shell used will be picked from the list of valid login shells (unless -f is used).
TERM: Carried over from the parent environment.

FILES

/etc/shells: Used as a source for valid login shells on systems where “getent shells” does not work.

EXAMPLES

Start a new shell in a new temporary directory:

$ shell
shell: info: Starting /bin/ksh in /tmp/shell-ksh.mJMHFTFE
$ exit
shell: info: Removing /tmp/shell-ksh.mJMHFTFE

Start a new dash shell in a temporary directory:

$ shell dash
shell: info: Starting /usr/local/bin/dash in /tmp/shell-dash.V7zU6EtZ
$ exit
shell: info: Removing /tmp/shell-dash.V7zU6EtZ

Start a new bash shell in a specific directory:

$ shell -d "$HOME/testing" bash
shell: info: Starting /usr/local/bin/bash in /home/myself/testing
$ exit
exit
shell: info: Leaving /home/myself/testing in place

Start ksh as a login shell and pre-populate the temporary directory with the contents of $HOME/skel. Note, starting the ksh shell as a login shell will in this case make it execute the .profile file copied from $HOME/skel.

$ shell -s "$HOME/skel" ksh -l
shell: info: Copying /home/myself/skel into /tmp/shell-ksh.ngEwbcpD
shell: info: Starting /bin/ksh in /tmp/shell-ksh.ngEwbcpD
$ ls -la
total 36
drwxr-xr-x   2 myself  wheel  512 Apr 15 12:55 .
drwxrwxrwt  28 root    wheel  512 Apr 21 14:15 ..
-rw-r--r--   1 myself  wheel   87 Nov  1 19:14 .Xdefaults
-rw-r--r--   1 myself  wheel  771 Feb  9 10:18 .cshrc
-rw-r--r--   1 myself  wheel  101 Nov  1 19:14 .cvsrc
-rw-r--r--   1 myself  wheel  359 Nov  1 19:14 .login
-rw-r--r--   1 myself  wheel  175 Nov  1 19:14 .mailrc
-rw-r--r--   1 myself  wheel  215 Feb  9 10:18 .profile
-rw-r--r--   1 myself  wheel  108 Apr 15 12:50 .vimrc
$ exit
shell: info: Removing /tmp/shell-ksh.ngEwbcpD

Start a POSIX-ly correct yash shell as another user.

$ su testuser -c 'shell yash --posixly-correct'
Password:
shell: info: Starting /usr/local/bin/yash in /tmp/shell-yash.yrSSGISG
$ id
uid=1001(testuser) gid=1001(testuser) groups=1001(testuser)
$ exit
shell: info: Removing /tmp/shell-yash.yrSSGISG

AUTHORS

Andreas Kusalananda Kähäri <andreas.kahari@abc.se>

CAVEATS

For Solaris, the list of valid login shells is taken from the “shells(4)” manual on a vanilla Solaris 11.4 system. This is because Solaris lacks “getent shells” and may also lack the /etc/shells file. The /etc/shells file will still be used if it exists.