How to produce a PS1 prompt in bash or ksh93 similar to tcsh

In ksh93:

PS1='${PWD#${PWD%?/*/*/*}?/} \$ ' share/doc/libnl-3-dev $ _ PS1='[${HOSTNAME%%.*}:${PWD#${PWD%?/*/*/*}?/}] $USER% ' [host:share/doc/libnl-3-dev] user% _ 

If you want it to also replace $HOME with ~, something nastier is needed:

PS1='$(d=${PWD/#$HOME/"~"};printf %s "${d#${d%?/*/*/*}?/}") $ ' ~/w/maemo $ cd sb2-pathmaps w/maemo/sb2-pathmaps $ _ PS1='$(d=${PWD/#$HOME/"~"};printf %s "[${HOSTNAME%%.*}:${d#${d%?/*/*/*}?/}]") $USER% ' [host:w/maemo/sb2-pathmaps] user% _ 

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All this should also work in bash, though bash has its own prompt escapes (eg. \h for ${HOSTNAME%%.*}) and path shortening mechanism (with PROMPT_DIRTRIM).

Also, the nastier variant will be really nasty, because bash, unlike ksh93, will fork() a separate process for each $(...; printf ...) command substitution, even if it contains only builtins. This also holds true for pdksh derived shells, like mksh.

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zsh has prompt escapes quite similar but not identical to tcsh:

zsh$ PS1='[%m:%3c] %n%# ' [host:share/doc/libnl-3-dev] user% _ 

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Note:

The $HOSTNAME variable is not set by default in ksh93; instead of it you could use the uname builtin (after enabling it with PATH=/opt/ast/bin:$PATH; the /opt/ast/bin path doesn't need to exist):

PS1='$(d=${PWD/#$HOME/"~"};h=$(uname -n); printf %s "[${h%%.*}:${d#${d%?/*/*/*}?/}]") $USER% ' 

Unlike the \h escape in bash or %m escape in zsh or tcsh this will track the hostname changes.

For bash, you could achieve similar results by setting the PROMPT_DIRTRIM variable:

$ PS1='[\u@\h] \w\$ ' [schaller@r2d2] ~$ pwd /home/schaller [schaller@r2d2] ~$ PROMPT_DIRTRIM=3 [schaller@r2d2] ~$ cd /home/schaller/tmp/513924/another/directory/here [schaller@r2d2] ~/.../another/directory/here$