PS1 – Changing the default bash prompt

There are all sorts of nifty tricks to customizing your bash prompt. I’m often switching between so many different servers that it its essential for me to always know the current user, server name, and current server time.

For customizing this, we have the PS1, PS2, PS3, PS4 session variables. I’m only going to touch on PS1 since that’s all I need to show me the current hostname and timestamp.

From the bash man pages:

       PROMPT_COMMAND
              If set, the value is executed as a command prior to issuing each primary prompt.
       PS1    The  value  of this parameter is expanded (see PROMPTING below) and used as the primary prompt string.  The default value is
              ââ\s-\v\$ ââ.
       PS2    The value of this parameter is expanded as with PS1 and used as the secondary prompt string.  The default is ââ> ââ.
       PS3    The value of this parameter is used as the prompt for the select command (see SHELL GRAMMAR above).
       PS4    The value of this parameter is expanded as with PS1 and the value is printed before each command  bash  displays  during  an
              execution  trace.   The  first  character  of PS4 is replicated multiple times, as necessary, to indicate multiple levels of
              indirection.  The default is ââ+ ââ.

First, you can view the current variable by echoing it:

[joe@svr ~]#echo $PS1
[\u@\h \W]\$
This is the default on all of my CentOS/RHEL 5.x servers. 
The bash man pages show us a full list of options and their meanings:

PROMPTING
       When executing interactively, bash displays the primary prompt PS1 when it is ready to read a command, and the secondary prompt PS2
       when  it  needs more input to complete a command.  Bash allows these prompt strings to be customized by inserting a number of back-
       slash-escaped special characters that are decoded as follows:
              \a     an ASCII bell character (07)
              \d     the date in "Weekday Month Date" format (e.g., "Tue May 26")
              \D{format}
                     the format is passed to strftime(3) and the result is inserted into the prompt string; an empty format results  in  a
                     locale-specific time representation.  The braces are required
              \e     an ASCII escape character (033)
              \h     the hostname up to the first â.â
              \H     the hostname
              \j     the number of jobs currently managed by the shell
              \l     the basename of the shellâs terminal device name
              \n     newline
              \r     carriage return
              \s     the name of the shell, the basename of $0 (the portion following the final slash)
              \t     the current time in 24-hour HH:MM:SS format
              \T     the current time in 12-hour HH:MM:SS format
              \@     the current time in 12-hour am/pm format
              \A     the current time in 24-hour HH:MM format
              \u     the username of the current user
              \v     the version of bash (e.g., 2.00)
              \V     the release of bash, version + patch level (e.g., 2.00.0)
              \w     the current working directory, with $HOME abbreviated with a tilde
              \W     the basename of the current working directory, with $HOME abbreviated with a tilde
              \!     the history number of this command
              \#     the command number of this command
              \$     if the effective UID is 0, a #, otherwise a $
              \nnn   the character corresponding to the octal number nnn
              \\     a backslash
              \[     begin a sequence of non-printing characters, which could be used to embed a terminal control sequence into the prompt
              \]     end a sequence of non-printing characters

       The command number and the history number are usually different: the history number of a command is its  position  in  the  history
       list,  which  may  include commands restored from the history file (see HISTORY below), while the command number is the position in
       the sequence of commands executed during the current shell session.  After the string is decoded,  it  is  expanded  via  parameter
       expansion,  command substitution, arithmetic expansion, and quote removal, subject to the value of the promptvars shell option (see
       the description of the shopt command under SHELL BUILTIN COMMANDS below).

 

By looking at this, we can string together what we’re looking for:

[\t \u@\h \W]$

This will show us the current time in seconds, the username, the hostname, and then the current working directory. For example:

[16:25:36 joe@svr /]$

To test it out, you can simply set your current bash variable:

[joe@svr ~]# PS1="[\t \u@\h \W]$ "

If you like what you see, you can make it permanent by adding it to your .bashrc file (/home/user/.bashrc). This is assuming that you only want to modify your profile. otherwise you’re going to want to look in /etc/bashrc

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