Let's say I have this alias in my .bashrc
alias somedir="cd /var/www/site"
how can I use somedir in say ... a cd command?
e.g.
cd somedir/app/
doing this currently returns:
-bash: cd: somedir/app: No such file or directory
Is it even possible to use an alias this way?
The bash shell has a CDPATH shell variable that helps you do this without an alias:
$ CDPATH=".:/var/www/site"
$ cd app
/var/www/site/app
If there's a subdirectory of app called doc:
$ cd app/doc
/var/www/site/app/doc
With a CDPATH value of .:/var/www/site, the cd command will first look in the current directory for the directory path given on the command line, and if none is found it will look under /var/www/site.
From the bash manual:
CDPATHThe search path for the
cdcommand. This is a colon-separated list of directories in which the shell looks for destination directories specified by thecdcommand. A sample value is".:~:/usr".
Note that CDPATH should not be exported as you usually do not want this variable to affect bash scripts that you run from your interactive session.
Quoting a handy Bash reference (emphasis mine):
A Bash alias is essentially nothing more than a keyboard shortcut, an abbreviation, a means of avoiding typing a long command sequence. ... It would be nice if aliases could assume some of the functionality of the C preprocessor, such as macro expansion, but unfortunately Bash does not expand arguments within the alias body. Moreover, a script fails to expand an alias itself within "compound constructs," such as if/then statements, loops, and functions. An added limitation is that an alias will not expand recursively. Almost invariably, whatever we would like an alias to do could be accomplished much more effectively with a function.
Notwithstanding your special case of CDPATH, as Kusalananda answered, an equivalent function might look like:
somedir() {
cd /var/www/site/"${1:-}"
}
Now you've got:
$ pwd
/tmp
$ somedir
$ pwd
/var/www/site
$ somedir app
$ pwd
/var/www/site/app
Aliases don't work that way, but you could use a variable instead:
somedir="/var/www/site"
cd "$somedir/app"
With due credit to Fox and RoVo for suggesting this in the comments
And if you want to save a few keystrokes, you could set up an alias:
alias somedir='cd "$somedir"'
Or if you enable autocd, you can cd by just giving the variable like a command:
~$ shopt -s autocd
~$ "$somedir"
/var/www/site$
cd cd /var/www/site/app(note the doublecd). Why not just use a variable?export SOMEDIR="/var/www/site"; cd "$SOMEDIR/app"somedir/app? (tried: answer no xD)