Thu, 02 Feb 2006
Command Return Codes and Long Command Prompts
Once you've been using a tool for a while you often reach a plateau where
it's "good enough" and you stop looking for ways to tweak it. I've been
using bash for a number of years and I've got set in my ways; until I
sat next to a co-worker who uses zsh.
My first Linux machine had a 14" monitor that could only do low resolutions. Screen space was at a premium and every character was precious. These days most of the machines I spend a lot of time on have 19-21 inch monitors. Unfortunately, I still have the same bash prompt.
As screen estate isn't quite so precious anymore I've changed to a two line prompt:
dwilson@fully.qualified.machine.name:/full/path/to/cwd/ $ type_commands_here
This gives me all the details of where I am (with each part allowing double click selection, ready for pasting in another terminal) while also having an almost empty line ready for my commands. While it still feels a little strange, after eight years of using a single line prompt, it's growing on me.
The other little bash tweak I've added recently, and this was inspired by
zsh, is to show all non-zero return codes from commands I've run in the
shell. As most of you know, a majority of unix command line tools return
'0' on success. If it returns a different exit code then something is
probably wrong. While you can check the exit code explicitly with an
'echo $?' this soon becomes very, very tedious. After
mentioning what I wanted to do, a number of sample command lines and
scripts bounced around the GLLUG list. After some discussion
Tethys came up with this little bit of magic:
show_exit_code() {
retval=$?
if [ $retval -ne 0 -a "$HISTCMD" != "$lastcmdnum" ];then
lastcmdnum="$HISTCMD"
echo " -- exit code: $retval"
fi
}
export PROMPT_COMMAND=show_exit_code
If you add this to your .bash_profile (or .bashrc if you source that) every time a command returns a non-zero code the shell will show it to you. This snippet also handles a number of the edge cases, it doesn't get in the way of piping, if a command returns a bad value and you press enter or Ctrl-C the code isn't displayed again and some other annoying bits my initial version didn't deal with.
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Posted: 2006/02/02 23:28 | /tools/commandline | Permanent link to this entry | This entry and same date
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