bash/globbing

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The following notes may apply to other shell environments besides bash, but have only been tested with bash.

Commands invoked via bash always, by default, have each of their arguments parsed via the glob system facility before being passed to the command.

Problems

This actively interferes with the ability of programs such as grep to behave intuitively when given a file-mask spec as input for processing, because:

wildcard obfuscation

  • any mask entered will apply only to the current folder.
  • folders are only included if their names also match the mask
    • ...thus not being useful as far as being the next layer of folders to search; the program will have to get its own directory listing for that.
  • applications are actively prevented from using wildcards in other ways that might be more intuitive in context, e.g.
    • a package-manager might allow you to list (or act on) packages whose names match a glob
    • a file-utility might want a glob to refer to the names of files being acted on, as a means of defining the *output* name
      • Examples:
        • "copy *.png *.backup.*" could mean "copy all .PNG files to this same folder but add ".backup" before the ".png"
          • NOTE: DOS utilities often made use of this convention.

inconsistency

Apparently the file-mask will be passed literally if no matches are found. (I guess this is useful so the program can say "no matches found for <filemask>", but...)

ambiguity

If there is a file whose name looks like an option because it begins with "-" or "--", and that file matches the file-mask given, the auto-globbing feature will include it verbatim in such a way that the executable may not be able to tell whether it's part of a file-listing or is actually an option from the command-line.

Workarounds

Globbing can be turned off on a per-session basis:

  • set -o noglob
    turns off globbing
    put it in ~/.bashrc to make it the default
  • set +o noglob
    turns globbing back on
  • help set
    returns more information about bash's set command (the "set" manpage is for something else)
  • Explicitly enclosing the filemask in quotes (double or single) suppresses auto-globbing. bash will strip off the quotes but not parse the contents.
    • The same is true for backslash-escaping the "*" character, as in \*.log

Related

Links

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