# The set builtin command

!!! warning "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`|`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)