Can I hook into the cd command?

With ksh or bash (or zsh):

cd() { builtin cd "$@" || return [ "$OLDPWD" = "$PWD" ] || case $PWD in (*/public_html) echo do something esac } 

With zsh:

chpwd() case $PWD in (*/public_html) echo do something esac 

(chpwd is a hook function that is called whenever the current working directory changes (by way of cd, pushd, popd...)).

Wrapping cd, an existing command, is not recommended.

A more universal solution would be defining a custom chpwd hook in Bash. (According to tags of this question, I assume you're using Bash)

There's not a complete hook system designed in Bash when compared with other modern shells. PROMPT_COMMAND variable is used as a hook function, which is equivalent to precmd hook in ZSH, fish_prompt in Fish. For the time being, ZSH is the only shell I've known that has a chpwd hook builtin.

PROMPT_COMMAND

If set, the value is interpreted as a command to execute before the printing of each primary prompt ($PS1).

https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html#Bash-Variables

chpwd Hook in Bash

A trick is provided to setup a chpwd equivalent hook in Bash based on PROMPT_COMMAND.

# create a PROPMT_COMMAND equivalent to store chpwd functions typeset -g CHPWD_COMMAND="" _chpwd_hook() { shopt -s nullglob local f # run commands in CHPWD_COMMAND variable on dir change if [[ "$PREVPWD" != "$PWD" ]]; then local IFS=$';' for f in $CHPWD_COMMAND; do "$f" done unset IFS fi # refresh last working dir record export PREVPWD="$PWD" } # add `;` after _chpwd_hook if PROMPT_COMMAND is not empty PROMPT_COMMAND="_chpwd_hook${PROMPT_COMMAND:+;$PROMPT_COMMAND}" 

Since we're detecting PWD change directly, the solution works with cd, pushd, and popd.

Note: The main difference between our chpwd implementaion in Bash and the chpwd in ZSH is, PROMPT_COMMAND is not supported in a non-interactive Bash shell.

Usage

_public_html_action() { if [[ $PWD == */public_html ]]; then # actions fi } # append the command into CHPWD_COMMAND CHPWD_COMMAND="${CHPWD_COMMAND:+$CHPWD_COMMAND;}_public_html_action" 

Source: Create chpwd Equivalent Hook in Bash from my gist.

For anyone want an answer for ZSH. Use chpwd hook in ZSH. Don't define chpwd() function directly. More detail here.

I am not a bash expert but I would take @UVV's answer and modify it just a little so that it does this:

• instead of checking for public_html, I'd just check for some hook-script file in the target dir $1, say, cd_hook.sh.
• if that hook-script exists, run it, and move on with the cd

This seems more generic because you'd then be able to apply the cd-hook to any directory if you so choose, by just adding a cd_hook.sh in the said directory.

Using powerful zsh approach in bash:

First an easy way to extend bash:

~/.runscripts

#load all scripts inside $1 dir run_scripts() { for script in $1/*; do # skip non-executable snippets [ -f "$script" ] && [ -x "$script" ] || continue # execute $script in the context of the current shell . $script done } 

Include in to .bashrc:

. ~/.run_scripts run_scripts ~/.bashrc.d 

You can create ~/.bashrc.d/cdhook with:

#!/bin/bash chpwd() { : #no action } cd() { builtin cd $1 chpwd $1 } 

Now is up to you to replace the function:

#list files after cd chpwd() { ls -lah --color }