It’s easy to delete all files in a directory:

$ rm *

However, making exceptions to this command is a little tricky. Suppose I have a LaTeX file (report.tex) in a directory, along with a shell script (createreport.sh) that processes this file to produce a PDF file (report.pdf) and/or a DVI file (report.dvi) and I want to keep only these files and delete all the temporary files created by the compiler—log, aux, etc. Normally, I’d include this deletion step in the contents of the shell script, perhaps like this,

#!/bin/bash

latex report || exit 1
pdflatex report || exit 1
rm -f *.aux
rm -f *.log
rm -f *.out
exit 0

This is a limited solution as it requires me to know beforehand, all the file extensions that I would want to delete. It would be great if I could tell rm to just spare the four original file extensions and delete anything else.

Extended Globs

To do that, use rm like this,

$ shopt -s extglob
$ rm -f !(*.+(tex|sh|pdf|dvi))

This is an example of nesting two extended globs. The explanation is found about a thousand lines into the bash manpage:

If the extglob shell option is enabled using the shopt builtin, several extended pattern matching operators are recognized.
In the following description, a pattern-list is a list of one or more patterns separated by a |. Composite patterns may be formed using one or more of the following sub-patterns:

?(pattern-list)
Matches zero or one occurrence of the given patterns

*(pattern-list)
Matches zero or more occurrences of the given patterns

+(pattern-list)
Matches one or more occurrences of the given patterns

@(pattern-list)
Matches one of the given patterns

!(pattern-list)
Matches anything except one of the given patterns

In my example, the first line enables the use of extended globs. Then, I used the +() glob to present a list of valid extensions and used a !() glob around that to exempt such files from deletion. So, rm will delete all files except .tex, .sh, .pdf or .dvi.

Going deeper

Since rm is a dangerous command to use, you can test out the test with ls or echo like this:

$ shopt -s extglob
$ ls !(*.+(tex|sh))
$ echo !(*.+(pdf|dvi))

This should print out the names of all files that are not .tex, .sh for the first example and not .pdf or .dvi files for the second example.

You can concoct similar negating tests for your needs:

Match files that don’t have a .xyz extension
```
  !(*.xyz)
```
Match files that don’t begin with abc
```
  !(abc*)
```
Match all files that don’t start with a, b, c, d or e
```
  !([a-e]*)
```
Match all files that don’t start with a or b and don’t end with c or d
```
  !(+(a|b)*+(c|d))
```

Extended Globs

Going deeper

Further reading