Wildcard

Wildcard is a "generalized" tool that helps you to operate in a pattern manner rather than a full name command / object. POSIX shell has 2 forms of wildcard:

1. Globbing
2. Regular Expression

Here, we will focus on #1 - Globbing in terminal command. In this example, we're going to use a directory that has the following files:

holloway:demo$ ls

abc     abcdefghijk  abc.php  abc.txt  ABC.txt   def  mydoc.odt  xyz.xml

abcdef  abcdef.odt   abctxt   abc.TXT  alphabet  DEF  xyz        xyz.yaml

Globbing

Globbing is the symbolic wildcards. There are useful in command searches like searching a list of item with X or Y pattern.

*

Asterisk symbolizes anything else that matches regardless length. Example:

holloway:demo$ ls a*

abc     abcdefghijk  abc.php  abc.txt  alphabet

abcdef  abcdef.odt   abctxt   abc.TXT

holloway:demo$ ls A*

ABC.txt

holloway:demo$ ls *.txt

abc.txt  ABC.txt

holloway:demo$ ls *txt

abctxt  abc.txt  ABC.txt

holloway:demo$ ls a*b*

abc     abcdefghijk  abc.php  abc.txt  alphabet

abcdef  abcdef.odt   abctxt   abc.TXT

holloway:demo$ ls *h*

abcdefghijk  abc.php  alphabet

?

Question mark is a length-specific symbolic wildcard regardless any character. Example:

holloway:demo$ ls D??

DEF

holloway:demo$ ls D?F

DEF

holloway:demo$ ls d??

def

holloway:demo$ ls *.???

abcdef.odt  abc.php  abc.txt  abc.TXT  ABC.txt  mydoc.odt  xyz.xml

holloway:demo$ ls *.????

xyz.yaml

[]

Character set to search one character listed inside the set. Example:

holloway:demo$ ls a[a-z]c.txt

abc.txt

holloway:demo$ ls a[0-9]c.txt

ls: cannot access 'a[0-9]c.txt': No such file or directory

holloway:demo$ ls a[a-z]?.txt

abc.txt

holloway:demo$ ls a[[:alpha:]]?.txt

abc.txt

holloway:demo$ ls a[[:alnum:]]?.txt

abc.txt

holloway:demo$ ls a[[:blank:]]?.txt

ls: cannot access 'a[[:blank:]]?.txt': No such file or directory

holloway:demo$ ls a[[:digit:]]?.txt

ls: cannot access 'a[[:digit:]]?.txt': No such file or directory

holloway:demo$ ls a[[:lower:]]?.txt

abc.txt

holloway:demo$ ls [[:upper:]][[:upper:]][[:upper:]].txt

ABC.txt

holloway:demo$ ls [[:xdigit:]][[:xdigit:]][[:xdigit:]].txt

abc.txt  ABC.txt

There are a list of regular expression ranges:

• [[:alnum:]] - A-Z, a-z, 0-9
• [[:alpha:]] - A-Z, a-z
• [[:blank:]] - Space, tab
• [[:cntl:]] - ASCII characters 0-31 (non-printing control characters)
• [[:digit:]] - 0-9
• [[:graph:]] - ASCII characters 0-31 (non-printing control characters)
• [[:lower:]] - a-z
• [[:print:]] - ASCII characters 32-127 (printable characters)
• [[:punct:]] - Punctuation (printable characters other than A-Z, a-z, 0-9)
• [[:space:]] - Space, Tab, LF (10), VT (11), FF (12), CR (13)
• [[:upper:]] - A-Z
• [[:xdigit:]] - 0-9, A-F, a-f

Toggle Globing and Shell Options Command

Sometimes, you might want to toggle the glob settings in your terminal. For this function, you need to refer back to the settings offered by your shell program. However, you have to double check each manually toggled options is POSIX compatible before use.

Not Supported

{}

curly brace expression is not supported in POSIX shell. Hence, you can't do something like:

holloway:demo$ ls abc.{txt,TXT}

You can however, workaround with grep regular expression:

holloway:demo$ ls abc.* | grep 'txt\|TXT'

abc.txt

abc.TXT

holloway:demo$

That's all about the wildcards. Feel free to proceed to the next section.