Linux

Globbing wildcard characters with zsh

Vincent Danen explains globbing with wildcard characters, and how using globbing in the z shell (zsh) yields powerful results.

Globbing is a way of expanding wildcard characters in a non-specific file name into a set of specific file names. Shells use globbing all the time. For instance:

$ ls foo*
foo1 foo2

When you enter the above, you're using a glob: foo*. What the shell is doing, however, is interpreting that wildcard character (*) and then passing the actual files to list to the ls command; so in this instance, the command that is actually being used is ls foo1 foo2.

Some standard wildcards that are often used include:

  • the asterisk (*) character for zero or more characters
  • the question mark (?) character for any single character
  • the [123] specifier, which indicates any of the characters 1, 2, or 3
  • the [0-9] specifier, which indicates any number between 0 and 9 (or [a-z] for any letters between a and z).

You can also use named ranges, such as:

  • [::alpha::] for any letter
  • [::alnum::] for any letter or number
  • [::lower::] for any lowercase character

When it comes to globbing, zsh is one of the most powerful shells with some very interesting wildcard characters that can be used. For instance, you can use glob qualifiers, which are characters with a special meaning. If you wanted to list all the symbolic link files in the current directory you would use:

$ ls *(@)

Some other zsh glob qualifiers include a forward slash (/) for directories and a period (.) for plain files; the zshexpn man page has a full list. If there are no matches, zsh will return an error; if there is nothing to pass to the ls program (or any other program), the program will not even be called by zsh.

There are other useful patterns, such as the (**/) pattern. What this does is tell zsh to match any number of directories to any depth, including the current directory. To find all the (*.sh) and (*.py) files in the current directory and sub-directories in a list suitable for parsing (i.e., perhaps in a script), you would use:

$ ls -1 **/*.(sh|py)

Finally, to enable extended globbing at all times, add this to ~/.zshrc:

setopt extended_glob

If you do decide to use extended globbing, be aware of special characters in file names and the need to quote them. For instance, if you want to copy files from a remote site using scp, you don't want zsh to expand any wildcards locally; you want that wildcard passed to scp for files on the remote end to match, so instead of:

$ scp hades:~/tmp/* .
zsh: no matches found: hades:~/tmp/*

You would need to use:

$ scp "hades:~/tmp/*" 

Delivered each Tuesday, TechRepublic's free Linux NetNote provides tips, articles, and other resources to help you hone your Linux skills. Automatically sign up today!

About

Vincent Danen works on the Red Hat Security Response Team and lives in Canada. He has been writing about and developing on Linux for over 10 years and is a veteran Mac user.

0 comments

Editor's Picks