Bash – How to Search Bash’s History in Vi Mode for ‘foo.*bar’

bash was initially designed in the late 80s as a partial clone of ksh with some interactive features from csh/tcsh.

The origins of globbing have to be found in those earlier shells which it builds upon.

ksh itself is an extension of the Bourne shell. The Bourne shell itself (first released in 1979 in Unix V7) was a clean implementation from scratch, but it did not depart completely from the Thompson shell (the shell of V1 -> V6) and incorporated features from the Mashey shell.

In particular, command arguments were still separated by blanks, | was now the new pipe operator but ^ was still supported as an alternative (and also explains why you do [!a-z] and not [^a-z]), $1 was still the first argument to a script and backslash was still the escape character. So many of the regexp operators (^\|$) have a special meaning of their own in the shell.

The Thompson shell relied on an external utility for globbing. When sh found unquoted *, [ or ?s in the command, it would run the command through glob.

rm *.txt

would end up running glob as:

["glob", "rm", "*.txt"]

and glob would end up running rm with the list of files matching that pattern.

grep a.\*b *.txt

would run glob as:

["glob", "grep", "a.\252b", "*.txt"]

The * above has been quoted by setting the 8th bit on that character, preventing glob from treating it as a wildcard. glob would then remove that bit before calling grep.

To do the equivalent with regexps, that would have been:

regexp rm '\.txt$'

Or:

regexp rm '^[^.].*\.txt$'

to exclude dot-files.

The need to escape the operators as they double as shell special characters, the fact that ., common in filenames is a regexp operator makes it not very appropriate to match filenames and complicated for a beginner. In most cases, all you need is wildcards that can replace either one (?) or any number (*) of characters.

Now, different shells added different globbing operators. Nowadays, the ksh and zsh globs (and to some extent bash -O extglob which implements a subset of ksh globs) are functionally equivalent to regexps with a syntax that is less cumbersome to use with filenames and the current shell syntax. For instance, in zsh (with extendedglob extension), you can do:

echo a#.txt

if you want (unlikely) to match filenames that consist of sequences of a followed by .txt. Easier than echo (^a*\.txt$) (here using braces as a way to isolate the regex operators from the shell operators which could have been one way shells could deal with it).

echo (foo|bar|<1-20>).(#i)mpg

For mpg files (case insensitive) whose basename is foo, bar or a decimal number from 1 to 20...

ksh93 now can also incorporate regexps (basic, extended, perl-like or "augmented") in its globs (though it's quite buggy) and even provides a tool to convert between glob and regexp (printf %R, printf %P):

echo ~(Ei:.*\.txt)

to match (non-hidden) txt files with Extended regular expressions, case-insensitively.

Your Ctrl-r is being intercepted by the kernel-based terminal cookied line processing engine.

While sleep is running, the terminal is in cooked mode, which means that the kernel-based tty line editor is working. The tty line editor supports rudimentary command line editing. The erase key (usually set to Ctrl-h (backspace) or Del) and the kill key (usually Ctrl-U) are the best known special editing keys that can be used in this mode. This line editor is useful: it's what lets interactive utilities that use neither readline nor curses to read complete lines of input from the terminal while allowing the user to make typing corrections.

But there's another special key that's active in this mode. You can see it along with the other key settings in the output of stty -a under the name rprnt and its default setting is... you guessed it... Ctrl-r. The function of this key is to repaint the current command line, in case it has become corrupted or misaligned due to other terminal output.

To avoid this, you can disable the function with stty rprnt undef.

Personally I am used to Ctrl-r being interpreted as a repaint command and I am surprised every time I try to do that in bash and it does something different!