# The set builtin command

FIXME incomplete - text, examples, maybe extended description

## Synopsis

    set [--abefhkmnptuvxBCHP] <-o OPTIONNAME> [-][--] <POSPARAMS>

## Description

`set` is primarily made to

-   set the positional parameters (see [handling positional
    parameters](../../scripting/posparams.md)) to `<POSPARAMS>`
-   set shell attributes with short options (see below)
-   set shell attributes with long option names (see below)

Without any options, `set` displays all shell- and environment-variables
(only is POSIX-mode) in a re-usable format `NAME=VALUE`.

### Attributes

All attributes below can be switched on using `-X` and switched off
using `+X`. This is done because of the historical meaning of the `-` to
set flags (true for most commands on UNIX(r)).

  Flag   Optionname                                                 Description
  ------ ---------------------------------------------------------- ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  `-a`   `allexport`                                                Automatically mark new and altered variables to be exported to subsequent environments.
  `-b`   `notify`                                                   Don't wait for the next prompt to print when showing the reports for a terminated background job (only with job control)
  `-e`   `errexit`                                                  When set, the shell exits when a simple command in a command list exits non-zero (`FALSE`). This is not done in situations, where the exit code is already checked (`if`, `while`, `until`, `||`, `&&`)
  `-f`   `noglob`                                                   Disable [pathname expansion](../../syntax/expansion/globs.md) (globbing)
  `-h`   `hashall`                                                  Remembers the location of commands when they\'re called (hashing). Enabled by default.
  `-k`   `keyword`                                                  Allows to place environment-assignments everywhere in the commandline, not only infront of the called command.
  `-m`   `monitor`                                                  **Monitor mode**. With job control, a short descriptive line is printed when a backgroud job ends. Default is \"on\" for interactive shells (with job control).
  `-n`   `noexec`                                                   Read and parse but **do not execute commands** - useful for checking scripts for syntax errors. Ignored by interactive shells.
  `-o`                                                              Set/unset attributes with long option names, e.g. `set -o noglob`. The long option names are in the second column of this table. If no option name is given, all options are printed with their current status.
  `-p`   `privileged`                                               Turn on privileged mode.
  `-t`   `onecmd`                                                   Exit after reading and executing **one** command.
  `-u`   `nounset`                                                  Treat unset variables as an error when performing parameter expansion. Non-interactive shells exit on this error.
  `-v`   `verbose`                                                  Print shell input lines as they are read - useful for debugging.
  `-x`   `xtrace`                                                   Print commands just before execution - with all expansions and substitutions done, and words marked - useful for debugging.
  `-B`   `braceexpand`                                              The shell performs [brace expansion](../../syntax/expansion/brace.md) This is on by default.
  `-C`   <BOOKMARK:tag_noclobber>`noclobber`                      Don't overwrite files on redirection operations. You can override that by specifying the `>|` redirection operator when needed. See [redirection](../../syntax/redirection.md)
  `-E`   `errtrace`                                                 `ERR`-traps are inherited by by shell functions, command substitutions, and commands executed in a subshell environment.
  `-H`   `histexpand`                                               Enable `!`-style history expansion. Defaults to `on` for interactive shells.
  `-P`   `physical`                                                 Don't follow symlinks when changing directories - use the physical filesystem structure.
  `-T`   `functrace`                                                `DEBUG`- and `RETURN`-traps are inherited by subsequent environments, like `-E` for `ERR` trap.
  `-`                                                               \"End of options\" - all following arguments are assigned to the positional parameters, even when they begin with a dash. `-x` and `-v` options are turned off. Positional parameters are unchanged (unlike using `--`!) when no further arguments are given.
  `--`                                                              If no arguments follow, the positional parameters are unset. With arguments, the positional parameters are set, even if the strings begin with a `-` (dash) like an option.
         Long options usable with `-o` without a short equivalent   
         `emacs`                                                    Use an emacs-style command line editing interface. This is enabled by default when the shell is interactive, unless the shell is started with `--noediting` option.
         `history`                                                  If set, command historization is done (enabled by default on interactive shells)
         `ignoreeof`                                                The effect is as if the shell command `IGNOREEOF=10` had been executed. See [shell variables](../../syntax/shellvars.md).
         `nolog`                                                    **(currently ignored)**
         `pipefail`                                                 If set, the exit code from a pipeline is different from the normal (\"last command in pipeline\") behaviour: `TRUE` when no command failed, `FALSE` when something failed (code of the rightmost command that failed)
         `posix`                                                    When set, Bash runs in POSIX mode.
         `vi`                                                       Enables a `vi`-style command line editing interface.

## Examples

Tag a part of a shell script to output debugging information (`-x`):

``` bash
#!/bin/bash
...
set -x # on
...
set +x # off
...
```

## Portability considerations

`set` and its basic behaviour and options are specified by POSIX(r).
However, options that influence Bash-specific things are not portable,
naturally.

## See also

-   Internal: [The shopt builtin command](../../commands/builtin/shopt.md)