Preventing duplicate entried in PATH (.cshrc)

cshpath

I need to prepend directories to the path variable in my .cshrc file and I want to make sure that the entries are not repeated when compared to existing directories in the path variable. Can someone advise suitable commands for that? The path on my machine is : separated, not space separated.

Best Answer

If on Linux, I suppose your csh is tcsh. Then you should be able to do:

set -f path=("/new/entry" $path:q)

In csh, tcsh and zsh, the $path special array variable is tied to the $PATH scalar environment variable in that the elements of the $path array are constructed by splitting the $PATH variable on the colon character. Any modification of either $path or $PATH is automatically reflected into the other variable.

-f above is to retain only the first entry. $path:q is the elements of $path, quoted, that is preventing word splitting. So the syntax above prepends the /new/entry or moves it to the front if it was already there.

Why would you be using csh though?

Note: the quotes above are necessary. Or more precisely, all the characters in /new/entry need to be quoted one way or another.

set -f path=('/new/'\e"ntry" $path:q)

is OK.

set -f path=(/'new/entry' $path:q)

is not. You can always do it in two stages though:

set path=(/new/entry $path:q)
set -f path=($path:q)

^{(one of the reasons you may want to stay away from csh)}

Related Solutions

Bash – Are Duplicate Entries in $PATH a Problem?

Having more entries in $PATH doesn't directly slow your startup, but it does slow each time you first run a particular command in a shell session (not every time you run the command, because bash maintains a cache). The slowdown is rarely perceptible unless you have a particularly slow filesystem (e.g. NFS, Samba or other network filesystem, or on Cygwin).

Duplicate entries are also a little annoying when you review your $PATH visually, you have to wade through more cruft.

It's easy enough to avoid adding duplicate entries.

case ":$PATH:" in
  *":$new_entry:"*) :;; # already there
  *) PATH="$new_entry:$PATH";; # or PATH="$PATH:$new_entry"
esac

Side note: sourcing someone else's shell script means executing code that he's written. In other words, you're giving your friends access to your account whenever they want.

Side note: .bashrc is not the right place to set $PATH or any other environment variable. Environment variables should be set in ~/.profile. See Which setup files should be used for setting up environment variables with bash?, Difference between .bashrc and .bash_profile.

Solaris – permanently update PATH for all users

Check /etc/default/login for login shells. You can force an initial path there.

Adding your variables to /etc/profile should work, depending on the version of Solaris running. A more portable, for Solaris, way of doing it would be to separate setting the PATH variable and exporting it.

JAVA_HOME=/usr/jdk/instances/jdk1.7.0
GROOVY_HOME=/usr/local/bin/groovy-2.1.3
PATH=${PATH}:${GROOVY_HOME}/bin:${JAVA_HOME}/bin
export PATH

Solaris 11, where bash is the default shell will work ok with your profile, but older Solaris version may not parse the export PATH=... syntax as expected, or at all.

Also, keep in mind that you're only changing the initial PATH for users. /etc/profile is read before a user's .profile is read.

By default, Solaris users will usually end up with their own .profile file that contains a default PATH.

solaris:~$ grep PATH .*
.profile:export PATH=/usr/bin:/usr/sbin

Since this .profile is being read in after the /etc/profile that you've modified, your changes to $PATH will be discarded and the user's entries will take over.

You can add these changes for new users by editing the file /etc/skel/.profile, but to make the changes permanent for existing users, you would need to edit their individual .profiles, or overwrite them if they haven't edited them themselves.

Best Answer

Related Solutions

Bash – Are Duplicate Entries in $PATH a Problem?

Solaris – permanently update PATH for all users

Related Question