Brackets, Braces, Curly Brackets in Bash
By John Thompson
Here goes the riddle:
If I do:
touch file{1,2,3}It creates file1, file2, file3
And if I do
rm file[1-3]It deletes them.
but if I do
touch file[1-3] it creates:
file[1-3]Why?
11 Answer
If you took the trouble of reading the manpage instead of making riddles:
Brace Expansion Brace expansion is a mechanism by which arbitrary strings may be generated. This mechanism is similar to pathname expansion, but the filenames generated need not exist.
...Pathname Expansion After word splitting, unless the -f option has been set, bash scans each word for the characters *, ?, and [. If one of these characters appears, then the word is regarded as a pattern, and replaced with an alphabetically sorted list of filenames matching the pattern (see Pattern Matching below). If no matching filenames are found, and the shell option nullglob is not enabled, the word is left unchanged.
...Pattern Matching Any character that appears in a pattern, other than the special pattern characters described below, matches itself. ... The special pattern characters have the following meanings: ... [...] Matches any one of the enclosed characters. A pair of characters separated by a hyphen denotes a range expression; any character that falls between those two characters, inclusive, using the current locale's collating sequence and character set, is matched.file[1-3] expands into files named file1, file2, file3. Filename expansion happens only if matching files exist. If not, the pattern is left as-is. Therefore, with files named file1, file2, file3, file[1-3] expands to file1 file2 file3. Without these files, it doesn't expand, and remains as file[1-3]. With {...}, the filenames don't have to exist, so file{1..3} expands to file1 file2 file3 irrespective of the files being present or absent.
