Skip to content

Latest commit

 

History

History
80 lines (53 loc) · 2.42 KB

shell-variables.md

File metadata and controls

80 lines (53 loc) · 2.42 KB
Raw

Shell Variables

variables are set by the shell

PATH

PATH The search path for commands.

  • It is a colon-separated list of directories in which the shell looks for commands (see COMMAND EXECUTION below).
  • A zero-length (null) directory name in the value of PATH indicates the current directory.
  • A null directory name may appear as two adjacent colons ::, or as an initial or trailing colon.
  • The default path is system-dependent, and is set by the administrator who installs bash.
  • A common value is
/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin

HISTFILE

HISTFILE

  • The name of the file in which command history is saved (see HISTORY below).
  • The default value is ~/.bash_history.
  • If unset, the command history is not saved when a shell exits.

HISTFILESIZE

  • The maximum number of lines contained in the history file.
  • When this variable is assigned a value, the history file is truncated, if necessary, to contain no more than that number of lines by removing the oldest entries.
  • The history file is also truncated to this size after writing it when a shell exits.
  • If the value is 0, the history file is truncated to zero size.
  • Non-numeric values and numeric values less than zero inhibit truncation.
  • The shell sets the default value to the value of HISTSIZE after reading any startup files.

HISTSIZE

  • The number of commands to remember in the command history (see HISTORY below).
  • If the value is 0, commands are not saved in the history list.
  • Numeric values less than zero result in every command being saved on the history list (there is no limit).
  • The shell sets the default value to 500 after reading any startup files.

PS*

PS1 主提示符

  • The value of this parameter is expanded (see PROMPTING below) and used as the primary prompt string.
  • The default value is \s-\v\$ .

PS2 次提示符

  • The value of this parameter is expanded as with PS1 and used as the secondary prompt string.
  • The default is > .

OSTYPE

OSTYPE Automatically set to a string that describes the operating system on which bash is executing. The default is system-dependent.

# e.g.
$ echo $OSTYPE
# on macOS : darwin*
darwin17.0
# on CentOS 7
linux-gnu

EPOCHSECONDS

It expands to the time in seconds since the Unix epoch.

( New in Bash 5.0 )

EPOCHREALTIME

It expands to the time in seconds since the Unix epoch with microsecond granularity.

( New in Bash 5.0 )