Wild cards

It's often boring to write all file names on a command line to give them as argument to a command. like:

cp genome_1.fasta genome_2.fasta genome_3.fasta all_genomes

There is in shell some special characters called wildcards that match several characters. There is mainly 4 kinds of wildcards:

the asterisk: *
the question mark ?
the square brackets []
the curly brackets {}

Asterisk Wildcard "*"

"*" is the most used wildcard, it matches no characters, any single characters or any string.

Question Mark Wildcard "?"

"?" that matches for exactly a single character.

Square Brackets Wildcard "[]"

Square brackets "[]" let you matches a range of values. For instance [abcd] match any character (only one) among a, b, c, d Instead of enumerating all allowed characters, we can used range [a-f] You can negate characters enclosed in Square brackets, using [^] => will match any character not in the list.

Warning

when you use a range, it uses the lexicographic order, so the result can be different, according to your locals. create a sandbox

~/XX$ mkdir XX
~/XX$ cd XX
~/XX$ touch {a,A,b,B}{01..10}

try with locals C

~/XX$ export LC_ALL=C
~/XX$ ls
A01  A03  A05  A07  A09  B01  B03  B05  B07  B09  a01  a03  a05  a07  a09  b01  b03  b05  b07  b09
A02  A04  A06  A08  A10  B02  B04  B06  B08  B10  a02  a04  a06  a08  a10  b02  b04  b06  b08  b10
~/XX$ ls -d [a-b]*
a01  a02  a03  a04  a05  a06  a07  a08  a09  a10  b01  b02  b03  b04  b05  b06  b07  b08  b09  b10
~/XX$ ls -d [ab]*
a01  a02  a03  a04  a05  a06  a07  a08  a09  a10  b01  b02  b03  b04  b05  b06  b07  b08  b09  b10

now change your local

~/XX$ export LC_ALL=en_US.UTF-8
~/XX$ ls
a01  a02  a03  a04  a05  a06  a07  a08  a09  a10  b01  b02  b03  b04  b05  b06  b07  b08  b09  b10
A01  A02  A03  A04  A05  A06  A07  A08  A09  A10  B01  B02  B03  B04  B05  B06  B07  B08  B09  B10
~/XX$ ls -d [ab]*
a01  a02  a03  a04  a05  a06  a07  a08  a09  a10  b01  b02  b03  b04  b05  b06  b07  b08  b09  b10
~/XX$ ls -d [a-b]*
a01  a02  a03  a04  a05  a06  a07  a08  a09  a10  b01  b03  b05  b07  b09
A01  A02  A03  A04  A05  A06  A07  A08  A09  A10  b02  b04  b06  b08  b10

if we use a range with an en_US.UTF-8 locals the file and directories starting with A or B are taken into account.

Curly Brackets Wildcard "{}"

Even "{}" is not really a wildcard, it is used in more or less in the same context. Curly brackets "{}" let you define a list of values.

{<START>..<END>}

Brace expansion using ranges is written giving the startpoint and the endpoint of the range. This is a "sequence expression". The sequences can be of two types:

integers (optionally zero padded, optionally with a given increment)
characters

$ echo {5..12}
5 6 7 8 9 10 11 12

$ echo {c..k}
c d e f g h i j k

When you mix these both types, brace expansion is not performed:

$ echo {5..k}
{5..k}

When you zeropad one of the numbers (or both) in a range, then the generated range is zeropadded, too:

$ echo {01..10}
01 02 03 04 05 06 07 08 09 10

Similar to the expansion using stringlists, you can add preamble and postscript strings:

$ echo 1.{0..9}
1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

$ echo ---{A..E}---
---A--- ---B--- ---C--- ---D--- ---E---

$ echo {A..Z}{0..9}
A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 B0 B1 B2 B3 B4 B5 B6 B7 B8 B9 C0 C1 C2 C3 C4 C5 C6
C7 C8 C9 D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 E0 E1 E2 E3 E4 E5 E6 E7 E8 E9 F0 F1 F2 F3
F4 F5 F6 F7 F8 F9 G0 G1 G2 G3 G4 G5 G6 G7 G8 G9 H0 H1 H2 H3 H4 H5 H6 H7 H8 H9 I0
I1 I2 I3 I4 I5 I6 I7 I8 I9 J0 J1 J2 J3 J4 J5 J6 J7 J8 J9 K0 K1 K2 K3 K4 K5 K6 K7
K8 K9 L0 L1 L2 L3 L4 L5 L6 L7 L8 L9 M0 M1 M2 M3 M4 M5 M6 M7 M8 M9 N0 N1 N2 N3 N4
N5 N6 N7 N8 N9 O0 O1 O2 O3 O4 O5 O6 O7 O8 O9 P0 P1 P2 P3 P4 P5 P6 P7 P8 P9 Q0 Q1
Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 R0 R1 R2 R3 R4 R5 R6 R7 R8 R9 S0 S1 S2 S3 S4 S5 S6 S7 S8
S9 T0 T1 T2 T3 T4 T5 T6 T7 T8 T9 U0 U1 U2 U3 U4 U5 U6 U7 U8 U9 V0 V1 V2 V3 V4 V5
V6 V7 V8 V9 W0 W1 W2 W3 W4 W5 W6 W7 W8 W9 X0 X1 X2 X3 X4 X5 X6 X7 X8 X9 Y0 Y1 Y2
Y3 Y4 Y5 Y6 Y7 Y8 Y9 Z0 Z1 Z2 Z3 Z4 Z5 Z6 Z7 Z8 Z9

$ echo {{A..Z},{a..z}}
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z a b c d e f g h i j k l m n o p q r s t u v w x y z

Common use and examples

Massdownload from the Web

In this example, wget is used to download documentation that is split over several numbered webpages.

wget won't see your braces. It will see 6 different URLs to download.:

wget http://docs.example.com/documentation/slides_part{1,2,3,4,5,6}.html

Of course it's possible, and even easier, to do that with a sequence:

wget http://docs.example.com/documentation/slides_part{1..6}.html

Generate a subdirectory structure

Your life is hard? Let's ease it a bit - that's what shells are here for.:

mkdir /home/bash/test/{foo,bar,baz,cat,dog}

(to go futher about brace expansion)

Escaping characters

Sometimes you need to tell the shell that it should ignore some characters that it normally interpreted as a special character or as a wild card. example

your filename contains a space (normaly interpreted as the command line separator)

your filename contains a * (asterisk), eg how to remove the file named "*" can you issue rm * ? (note don't try that)

there is various solutions to escape special characters.

use the character \ (backslash) to protect the spurious character.
enclose file name in ' (single-quotes) or " (double-quotes)