Matching file names using path name expansions

Globbing: Path name Expansion
Bash shell has a capability of path name matching, which is known as Globbing. To understand globbing we need to know about the “wildcard”.
It’s nothing but a set of building blocks that allows to create a pattern which define a set of files or directories. There are 3 basic set of wildcard –
* – It represents any string of zero or more characters
? – It represents a single character
[ ] – It represents a range of characters

Pattern Matching –
Globbing is an operation that expands a wildcard pattern into the list of path-names matching the pattern. Bash itself cannot recognize Regular Expressions. Command-line meta-characters are replaced by the match list prior to execution any command. So, Let starts with the common meta characters and pattern classes along with the demonstration.
A simple set of files and directories are useful to demonstrate expansion.

[[email protected] ~]# mkdir pattern

[[email protected] ~]# mkdir pattern
[[email protected] ~]# cd pattern 
[[email protected] pattern]# touch arch backtrack centos debian elive fedora amigo beatrIX conectiva deli floppix 
[[email protected] pattern]# ls amigo  backtrack  centos     debian  elive   floppix arch   beatrIX    conectiva  deli    fedora 
[[email protected] pattern]#

First, make pattern matching by using *

[[email protected] pattern]# ls a* 
 amigo  arch

[[email protected] pattern]# ls i 
 amigo  conectiva  debian  deli  elive  floppix

Pattern matching by using ?

[[email protected] pattern]# ls ?????? 
 centos  debian  fedora

[[email protected] pattern]# ls a??? 
 arch
 

 
[[email protected] pattern]# ls ?e???? 
centos  debian  fedora  

[email protected] pattern]# ls *i? 
 floppix

Pattern Matching by using [] –

[[email protected] pattern]# ls [ab]* 
 amigo  arch  backtrack  beatrIX

[[email protected] pattern]# ls [d]* 
 debian  deli

[[email protected] pattern]# ls *[^ao] 
 arch  backtrack  beatrIX  centos  debian  deli  elive  floppix 

caret ( ^ ) means look for character which is not contains the characters which are mentioned inside the brackets. In above example all the name which contains “a” or “o” at the end are not listed.

Brace expansion –
It is used to generate discretionary strings of characters. Brace expansions can also be nested.

[[email protected] ~]# mkdir expansion; cd expansion

[[email protected] expansion]# touch {c,php,html,ruby,fortan,assembly,javascripts}.txt 

[[email protected] expansion]# ls 
 assembly.txt  c.txt  fortan.txt  html.txt  javascripts.txt  php.txt  ruby.txt

[[email protected] expansion]# touch file{A..F}.txt; ls 
 fileA.txt  fileB.txt  fileC.txt  fileD.txt  fileE.txt  fileF.txt 

[[email protected] expansion]# touch file{a..d}{1,2}.txt; ls
  filea1.txt  fileb1.txt  filec1.txt  filed1.txt 
 filea2.txt  fileb2.txt  filec2.txt  filed2.txt 

[[email protected] expansion]# touch file{a{1,3,8},b{2,3},c}.txt; ls 
 filea1.txt  filea3.txt  filea8.txt  fileb2.txt  fileb3.txt  filec.txt