Tuesday Tiny Techie Tip

Globbing

Globbing is what lets you use a pattern to match one or more files:

% rm *.*

* ("splat", or "asterisk", or "nathan hale")

The splat is your basic steamroller of file matching. A splat all by itself matches any string of characters, and thus all files (except "dot"-files and this is the last time I'll point that out) combined with other literal characters, or other glob characters, it indicates parts of the filename which are allowed to vary wildly. Some examples:

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[show all files]

% ls *
adb.1                   dd.1                    ld.so.1
addbib.1                ed.1                    ldd.1
adjacentscreens.1       edit.1                  od.1v
admin.1                 fdformat.1              pdp11.1
cd.1                    id.1v                   rdist.1
cdc.1                   ld.1                    sdiff.1v

[show all files that end in ".1v"]

% ls *.1v
id.1v           od.1v           sdiff.1v

[show all files that start with "a" and have a "b"]

% ls a*b*
adb.1           addbib.1

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? (question mark)

The question mark matches exactly one character (any character). Examples:

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[show all files with at least 5 characters in their names]

% ls ?????*
addbib.1                fdformat.1              pdp11.1
adjacentscreens.1       id.1v                   rdist.1
admin.1                 ld.so.1                 sdiff.1v
cdc.1                   ldd.1                   
edit.1                  od.1v

[show all files with a 2-character extension]

% ls *.??
id.1v           od.1v           sdiff.1v

[show all files whose third letter is "d"]

% ls ??d*
addbib.1        ldd.1

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[] (square brackets)

Square brackets give a list of characters to match. Only one character is matched by each occurrence of square brackets. You can kind of think of them as a question mark match with a little more control. You can also do the negative match case by putting a "^" (caret, shift-6) as the first character in the class. (In the Bourne shell and friends, the negation character is "!" (bang))

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[show all files that start with "a" or "e"]

% ls [ae]*
adb.1                   adjacentscreens.1       ed.1
addbib.1                admin.1                 edit.1

[show all files that don't start with "a" or "e"]

% ls [^ae]*
cd.1            fdformat.1      ld.so.1         pdp11.1
cdc.1           id.1v           ldd.1           rdist.1
dd.1            ld.1            od.1v           sdiff.1v

[show all files that have a "c" or "h" extension]

% ls *.[ch]

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% ls z*
ls: No match.

% set nonomatch
% ls z*
z* not found

The final matching construct is only available in csh and its derivatives, and is not subject to the "No match" problems:

{} (curly brackets)

Curly brackets enclose a list of alternative strings separated by commas. Unlike with the other matching operators, the alternatives are expanded without any reference to the available files, and before the other wildcard operators are expanded. For example, if you used the pattern "{foo,bar}*", the pattern would first be expanded to "foo* bar*", and then the splats would be matched against files before the command would be called. Examples:

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[show all files whose first character is "a" or "b" and second is "c" or "d"]

% ls {a,b}{c,d}*
adb.1                   adjacentscreens.1
addbib.1                admin.1

[show all files that start with "ed" or "ld"]

% ls {ed,ld}*
ed.1    edit.1  ld.1    ld.so.1 ldd.1

[show all files that have a "cc" or "hh" extension]

% ls *.{cc,hh}

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Since the curly brackets don't pay any attention to the available files, you can also use them to generate strings (or count in base 3 ;-):

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% echo {0,1,2}{0,1,2}{0,1,2} | fmt -36
000 001 002 010 011 012 020 021 022
100 101 102 110 111 112 120 121 122
200 201 202 210 211 212 220 221 222

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