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echo: Displays a specified line of text env: Displays and modifies environment variables: expr: Evaluates expressions factor: Factors numbers: false: Does nothing, but exits unsuccessfully groups: Prints the groups of which the user is a member hostid: Prints the numeric identifier for the current host id: Prints real or effective UID and GID ...
sudo retains the user's invocation rights through a grace period (typically 5 minutes) per pseudo terminal, allowing the user to execute several successive commands as the requested user without having to provide a password again. [21] As a security and auditing feature, sudo may be configured to log each command run.
The control structures, expression grammar, history mechanism and other features in Holub's SH were identical to those of the C shell. In 1988, Hamilton Laboratories began shipping Hamilton C shell for OS/2. [23] It included both a csh clone and a set of Unix-like utilities. In 1992, Hamilton C shell was released for Windows NT. [24]
echo began within Multics.After it was programmed in C by Doug McIlroy as a "finger exercise" and proved to be useful, it became part of Version 2 Unix. echo -n in Version 7 replaced prompt, (which behaved like echo but without terminating its output with a line delimiter).
A common value is /bin/sh, but some systems such as Solaris have the POSIX-compatible shell at /usr/xpg4/bin/sh. [13] In many Linux systems, /bin/sh is a hard or symbolic link to /bin/bash, the Bourne Again shell (BASH). Using bash-specific syntax while maintaining a shebang pointing to sh is also not portable. [14]
$ # bash shell $ /bin/bash-c 'echo a{p,c,d,b}e' ape ace ade abe $ # A traditional shell does not produce the same output $ /bin/sh-c 'echo a{p,c,d,b}e' a{p,c,d,b}e When brace expansion is combined with wildcards, the braces are expanded first, and then the resulting wildcards are substituted normally.
will answer the prompts for confirmation with y, effectively installing foobar with sudo apt without any prompts. This usage may be obsolete today, as most commands that would request response from the user have either a 'force' option (e.g., rm-f) or an 'assume-yes' option (for example,apt-y). As an example, the following: $
In computing, pushd and popd are a pair of commands which allow users to quickly switch between the current and previous directory when using the command line. When called, they use a directory stack to sequentially save and retrieve directories visited by the user.