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Full Discussion: Changing PS1
Top Forums Shell Programming and Scripting Changing PS1 Post 302733521 by alister on Tuesday 20th of November 2012 03:36:03 PM
Old 11-20-2012
Quote:
Originally Posted by Corona688
Insert a 'true' after it to force $? back to 0.

Unfortunately this will change the value of $? if you were wanting to depend on it later...
Command substitution never affects the value of $?, and that's the only way to execute anything from within the prompt string.

I don't think it's possible to cause the expansion of PS1 to alter the value of $?. If you (or anyone else) knows of a way, I'd appreciate knowing about it.


Quote:
Originally Posted by kristinu
Code:
    PS1="\[\033[0;37m\]\342\224\214\342\224\200 ...

My problem is that if I just press enter, I do not want to have the ✗ printed.
Since you neglected to be specific, I'm assuming this is for bash.

It seems like what you need is a way to detect when no command was entered at the prompt. Bash makes available the command number through the escape sequence \#. This value (at least with the version with which I tested) is not incremented for a null command. Testing its current value against its value at the time of the previous prompt's expansion should be sufficient to make a determination.

Since any variables set in the command substition subshell are lost when the shell exists, and since environmental changes cannot propagate from a child to a parent, the only way to store the command number for future inspection is to write it to a file.

The following example is intended only as a proof of concept. Aside from the minor inefficiency of reading a file for each prompt, it doesn't support simultaneously interactive shells (although it could, with some work and help from $$). The prompt consists simply of the exit status followed by a colon and a space. If no command was entered, regardless of the value of $?, a 0 is printed (analgous to not printing the X in your original problem statement):
Code:
PS1='$(ES=$?; LC=$(< ~/.lastcmd); if [ \# -eq ${LC:-0} ]; then echo 0; else echo $ES; fi; echo \# > ~/.lastcmd): '

Regards,
Alister
 

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LEARN ABOUT DEBIAN

seesat5

seesat5(1)						      General Commands Manual							seesat5(1)

NAME

       seesat5 - provides satellite visibility information.

SYNOPSIS

       seesat5 [ report ] [ go <Label> ] | [ <command> ... ]

DESCRIPTION

       This  program uses the sgp4 algorithm provided by NORAD to produce position information on a satellite. Seesat5 can produce tracking infor-
       mation for one satellite over a period of several days, or for a collection of satellites over that period. By providing filter	conditions
       seesat5 prints out only those satellites you might have a chance to see rather than all the satellites that pass above the horizon.

       Seesat5	is  typically  run  by placing control commands into an init file called SEESAT5.INI. See seesat5 (7) for the description of these
       commands.  If there is no init file Seesat5 will present the operator with a '>' prompt where commands can  be  entered.  From  the  prompt
       seesat5 will begin analysis when sufficient parameters have been entered to begin the run.

       Seesat5	uses  selection  conditions to filter the data so that only high and bright satellites are printed. Note that the selection condi-
       tions are used to select whether or not the current passes data will be printed. If it is printed, then the complete pass data is  printed.
       ie. all data from when the satellite comes over the horizon until it goes below.

       For lines that satisfied ALL the selection conditions, a "+" sign is printed as the first character.

   Options
       report This  option  will disable printing of report records in the output of the run. These include all command lines found in SEESAT5.INI
	      or entered from the command line or the prompt.

       go     Followed by a label, this option causes branching within the SEESAT5.INI to begin execution at the line following  label.  Branching
	      occurs when the cmdline command is executed in the SEESAT5.INI file.

       command
	      Most of the commands that can be found in SEESAT5.INI can be entered on the command line. If you desire the SEESAT5.INI file to exe-
	      cute after the command line be sure to make the last command RET.

FILES

       SEESAT5.INI
	      The control file for seesat5

       *.tle  Two line element files used by seesat5.

SEE ALSO

       seesat5(7), SEESAT5.INI(5), tle(5), cr(1)

BUGS

       Seesat5 is not always able to check data integrity. Since computation and output is driven by the data in  the  two  line  element,  subtle
       errors  in  a  tle can cause floating point exceptions. In addition there are several commands that do not work well together, like SHOWTLE
       and RUNTIME. Please report any problems with seesat5 to Dale Scheetz <dwarf@polaris.net>.

Debian Linux							    28 March 96 							seesat5(1)
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