[SOLVED] Doubt about PS1

El Rengo · 06-27-2020, 10:21 PM

Hi! I've a doubt with PS1 prompt customization. I've my own PS1 config on .bashrc file. I shared:

Code:

####################################################################################################
# List of Colors
##########################################################################################################

# Reset
Color_Off='\e[0m'       # Text Reset

# Regular Colors
Black='\e[0;30m'        # Black
Red='\e[0;31m'          # Red
Green='\e[0;32m'        # Green
Yellow='\e[0;33m'       # Yellow
Blue='\e[0;34m'         # Blue
Purple='\e[0;35m'       # Purple
Cyan='\e[0;36m'         # Cyan
White='\e[0;37m'        # White

# Bold
BBlack='\e[1;30m'       # Black
BRed='\e[1;31m'         # Red
BGreen='\e[1;32m'       # Green
BYellow='\e[1;33m'      # Yellow
BBlue='\e[1;34m'        # Blue
BPurple='\e[1;35m'      # Purple
BCyan='\e[1;36m'        # Cyan
BWhite='\e[1;37m'       # White

# Underline
UBlack='\e[4;30m'       # Black
URed='\e[4;31m'         # Red
UGreen='\e[4;32m'       # Green
UYellow='\e[4;33m'      # Yellow
UBlue='\e[4;34m'        # Blue
UPurple='\e[4;35m'      # Purple
UCyan='\e[4;36m'        # Cyan
UWhite='\e[4;37m'       # White

# Background
On_Black='\e[40m'       # Black
On_Red='\e[41m'         # Red
On_Green='\e[42m'       # Green
On_Yellow='\e[43m'      # Yellow
On_Blue='\e[44m'        # Blue
On_Purple='\e[45m'      # Purple
On_Cyan='\e[46m'        # Cyan
On_White='\e[47m'       # White

# High Intensity
IBlack='\e[0;90m'       # Black
IRed='\e[0;91m'         # Red
IGreen='\e[0;92m'       # Green
IYellow='\e[0;93m'      # Yellow
IBlue='\e[0;94m'        # Blue
IPurple='\e[0;95m'      # Purple
ICyan='\e[0;96m'        # Cyan
IWhite='\e[0;97m'       # White

# Bold High Intensity
BIBlack='\e[1;90m'      # Black
BIRed='\e[1;91m'        # Red
BIGreen='\e[1;92m'      # Green
BIYellow='\e[1;93m'     # Yellow
BIBlue='\e[1;94m'       # Blue
BIPurple='\e[1;95m'     # Purple
BICyan='\e[1;96m'       # Cyan
BIWhite='\e[1;97m'      # White

# High Intensity backgrounds
On_IBlack='\e[0;100m'   # Black
On_IRed='\e[0;101m'     # Red
On_IGreen='\e[0;102m'   # Green
On_IYellow='\e[0;103m'  # Yellow
On_IBlue='\e[0;104m'    # Blue
On_IPurple='\e[0;105m'  # Purple
On_ICyan='\e[0;106m'    # Cyan
On_IWhite='\e[0;107m'   # White

##########################################################################################################
# Custom prompt
##########################################################################################################

PS1="[\[$BGreen\]\w\[$Color_Off\]]\n[\[$BIRed\]\u\[$BWhite\]@\[$BIBlue\]\h\[$Color_Off\]]\\$ "

I do not undertand why for "\w" or "\u" or "\h" I do not need double "" but for "\$" it's required "\\$"
Thanks!

elrengo!

ondoho · 06-28-2020, 04:49 AM

Quote:

Originally Posted by El Rengo

I do not undertand why for "\w" or "\u" or "\h" I do not need double "" but for "\$" it's required "\\$"

One is an actual $ sign, the other changes depending on which user you are:

Code:

#PS1="\$"
$PS1="\\$"
#PS1="\$"
$whoami
root
$PS1="\$"
$PS1="\\$"
#exit
logout
$whoami
ondoho
$PS1="\$"
$PS1="\\$"
$whoami
ondoho

pan64 · 06-28-2020, 05:02 AM

Quote:

Originally Posted by El Rengo

I do not undertand why for "\w" or "\u" or "\h" I do not need double "" but for "\$" it's required "\\$"

You need to think a bit differently: \ and the following char together (as an expression) has a special meaning.
\w, \u, \h or \\.
Additionally it is evaluated once when you set PS1 and second time when it printed. \w and \u should be evaluated that time (when printed), but $ at the end should be taken as is.
So \\ will be \ at the first step and \$ will be $ at the second.

El Rengo · 06-28-2020, 10:55 AM

Quote:

Originally Posted by ondoho

One is an actual $ sign, the other changes depending on which user you are:

Code:

#PS1="\$"
$PS1="\\$"
#PS1="\$"
$whoami
root
$PS1="\$"
$PS1="\\$"
#exit
logout
$whoami
ondoho
$PS1="\$"
$PS1="\\$"
$whoami
ondoho

Thanks! I know that and for that I would like to use "\$". Because I use the same .bashrc file for root and my user. Using "\$" allow to me use the same .bashrc and know if i have a UI=0 or not.

Quote:

Originally Posted by pan64

You need to think a bit differently: \ and the following char together (as an expression) has a special meaning.
\w, \u, \h or \\.
Additionally it is evaluated once when you set PS1 and second time when it printed. \w and \u should be evaluated that time (when printed), but $ at the end should be taken as is.
So \\ will be \ at the first step and \$ will be $ at the second.

Thanks! I believe all "\character" have the same behavior.

GazL · 06-28-2020, 04:59 PM

Quote:

Originally Posted by El Rengo

I do not undertand why for "\w" or "\u" or "\h" I do not need double "" but for "\$" it's required "\\$"

The rules for double-quotes are a little involved (and have historically differed between shell implementations).

For bash, within double-quotes, '\' only keeps its special meaning (i.e. escape the next character) when it proceeds one of: $ ` \ "
In all other cases it is treated literally.

So
word="\\u" and word="\u" will both set $word to be '\u'
but
word="\\$" and word="\$" will set $word to '\$' and '$' respectively.

Sometimes you're just better off not using double-quotes at all. It may make the assignment a little longer because you might need a few extra '\' in order to get the desired value, but at least '\' acts consistently outside of double quotes, no matter what it proceeds.

El Rengo · 06-28-2020, 06:55 PM

Quote:

Originally Posted by GazL

The rules for double-quotes are a little involved (and have historically differed between shell implementations).

For bash, within double-quotes, '\' only keeps its special meaning (i.e. escape the next character) when it proceeds one of: $ ` \ "
In all other cases it is treated literally.

So
word="\\u" and word="\u" will both set $word to be '\u'
but
word="\\$" and word="\$" will set $word to '\$' and '$' respectively.

Sometimes you're just better off not using double-quotes at all. It may make the assignment a little longer because you might need a few extra '\' in order to get the desired value, but at least '\' acts consistently outside of double quotes, no matter what it proceeds.

Thanks! But if I use a "'":

Code:

PS1='[\[$BGreen\]\w\[$Color_Off\]]\n[\[$BIRed\]\u\[$BWhite\]@\[$BIBlue\]\h\[$Color_Off\]]\$ '

the result is:

Code:

Last login: Sun Jun 28 20:42:55 2020 from X.X.X.X
[\e[1;32m~\e[0m]
[\e[1;91melrengo\e[1;37m@\e[1;94mlab-oss1\e[0m]$

pan64 · 06-29-2020, 02:13 AM

because evaluation works differently with ' and ". Actually ' disables almost everything.
https://stackoverflow.com/questions/...quotes-in-bash

GazL · 06-29-2020, 03:02 AM

My suggestion was to not use any quotes when setting PSn

Here's mine, as example:

Code:

# ANSI Terminal control sequences to implement text styles,
# for use in prompts (and/or elsewhere):
declare -A style=(
  [default]=$( tput -S <<< $'sgr0\nop' )
  [prompt]=$( tput -S <<< $'sgr0\nop\nbold' )
  [input]=$( tput -S <<< $'sgr0\nop\nbold\nsetaf 5' )
  [warning]=$( tput -S <<< $'sgr0\nop\nbold\nsetaf 3' )
  [error]=$( tput -S <<< $'sgr0\nop\nbold\nsetaf 1' )
)

# Bash prompts:
#   'trap' ensures we clean up after ourselves on exit.
trap "tput -S <<< $'sgr0\nop'" EXIT
PS1=\\[${style[prompt]}\\]\\$\ \\[${style[input]}\\]
PS2=\\[${style[prompt]}\\]\>\ \\[${style[input]}\\]
PS0=${style[default]}

As I said above, you get a few extra '\' along the way, but the rules remain consistent.