Expressions Régulières et Wildcards¶

In the GNU/Linux operating system, regular expressions and wildcards often have the same symbol (or style), so people often confuse them.

What is the difference between regular expressions and wildcards?

Similitudes :

They have the same symbol but represent entirely different meanings.

Différences :

Regular expressions match file content; Wildcards are typically used to match file or directory names.
Regular expressions are typically used on commands such as grep, sed, awk, and so on.
Les caractères génériques sont couramment utilisés avec des commandes telles que cp, find, mv, touch, ls, etc.

Wildcards et GNU/Linux¶

GNU/Linux operating systems support these wildcards:

style de wildcards	Rôle
?	Matches one character of a file or directory name.
*	Matches 0 or more arbitrary characters of a file or directory name.
[ ]	Matches any single character in parentheses. For example, [one] which means to match o or n or e.
[-]	Matches any single character within the given range in parentheses. For example, [0-9] matches any single number from 0 to 9.
[^]	"logical non" matching of a single character. For example, [^a-zA-Z] represents matching a single non-letter character.
{,}	Non continuous matching of multiple single characters. Séparés par des virgules.
{..}	Tout comme [-]. Par exemple, {0..9} et {a..z}

Different commands have different support for wildcard styles:

find: prend en charge *, ?, [ ], [-], [^]
ls: All supported
mkdir: prend en charge {,} and {..}
touch: prend en charge {,} and {..}
mv : tous pris en charge
cp : tous pris en charge

Par exemple :

Shell > mkdir -p /root/dir{1..3}
Shell > cd /root/dir1/
Shell > touch file{1,5,9}
Shell > cd 
Shell > mv /root/dir1/file[1-9]  /root/dir2/
Shell > cp /root/dir2/file{1..9} /root/dir3/
Shell > find / -iname "dir[1-9]" -a -type d

Regular expressions in GNU/Linux¶

Two major schools of regular expressions exist due to historical development:

POSIX :
BRE（basic regular expression）
ERE (expression régulière étendue)
Classe de caractères POSIX
PCRE (Perl Compatible Regular Expressions): The most common among various programming languages.

	BRE	ERE	Classe de caractères POSIX	PCRE
`grep`	√	√ (nécessite l'option -E)	√	√ (nécessite l'option -P)
`sed`	√	√ (nécessite l'option -r)	√	×
`awk`	√	√	√	×

For more on regular expressions, visit this website for more helpful information.

BRE¶

BRE (Basic Regular Expression) is the oldest type of regular expression, introduced by the grep command in UNIX systems and the ed text editor.

métacaractère	Description	exemple bash
*	Matches the number of occurrences of the previous character, which can be 0 or any number of times.
.	Matches any single character except for line breaks.
^	Correspond au début de ligne. For example - ^h will match lines starting with h.
$	Prend la fin de ligne EOL en considération. For example - h$ will match lines ending in h.
[]	Matches any single character specified in parentheses. For example - [who] will match w or h or o; [0-9] will match one digit; [0-9][a-z] will match characters composed of one digit and a single lowercase letter.
[^]	Matches any single character except for the characters in parentheses. For example - [^0-9] will match any single non-numeric character. [^a-z] will match any single character that is not a lowercase letter.
\	Escape character, used to cancel the meaning represented by some special symbols.	`echo -e "1.2\n122" \\\| grep -E '1\.2'` 1.2
\{n\}	Matches the number of occurrences of the previous single character, n represents the number of matches.	`echo -e "1994\n2000\n2222" \\\| grep "[24]\{4\}"` 2222
\{n,\}	Matches the previous single character at least n times.	`echo -e "1994\n2000\n2222" \\\| grep "[29]\{2,\}"` 1994 2222
\{n,m\}	Matches the previous single character at least n times and at most m times.	`echo -e "abcd\n20\n300\n4444" \\\| grep "[0-9]\{2,4\}"` 20 300 4444

ERE¶

métacaractère	Description	exemple bash
+	Matches the number of occurrences of the previous single character, which can be 1 or more times.	`echo -e "abcd\nab\nabb\ncdd" \\\| grep -E "ab+"` abcd ab abb
?	Matches the number of occurrences of the previous single character, which can be 0 or 1.	`echo -e "ac\nabc\nadd" \\\| grep -E 'a?c'` ac abc
\<	Boundary character, matching the beginning of a string.	`echo -e "1\n12\n123\n1234" \\\| grep -E "\<123"` 123 1234
\>	Boundary character, matching the end of the string.	`echo -e "export\nimport\nout" \\\| grep -E "port\>"` export import
()	Combinatorial matching, that is, the string in parentheses as a combination, and then match.	`echo -e "123abc\nabc123\na1b2c3" \\\| grep -E "([a-z][0-9])+"` abc123 a1b2c3
\		The pipeline symbol represents the meaning of "or".

ERE also supports characters with special meanings:

caractères spéciaux	Description
\w	Équivalent à [a-zA-Z0-9]
\W	Équivalent à [^a-zA-Z0-9]
\d	Équivalent à [0-9]
\D	Équivalent à [^0-9]
\b	Équivalent à \< or \>
\B	Matches non-boundary character.
\s	Matches any whitespace character. Équivalent à [ \f\n\r\t\v]
\S	Équivalent à [^ \f\n\r\t\v]

Caractère blanc	Description
\f	Matches a single feed character. Équivalent à \x0c et \cL
\n	Matches individual line breaks. Équivalent à \x0a et \cJ
\r	Matches a single carriage return. Équivalent à \x0d et \cM
\t	Correspond à un onglet unique. Équivalent à \x09 et \cI
\v	Matches a single vertical tab. Équivalent à \x0b et \cK

Caractère POSIX¶

Sometimes, you may see "POSIX character"(also known as "POSIX character class"). Please note that the author rarely uses the "POSIX character class", but has included this section to enhance basic understanding.

Caractère POSIX	équivalent à
[:alnum:]	[a-zA-Z0-9]
[:alpha:]	[a-zA-Z]
[:lower:]	[a-z]
[:upper:]	[A-Z]
[:digit:]	[0-9]
[:space:]	[ \f\n\r\t\v]
[:graph:]	[^ \f\n\r\t\v]
[:blank:]	[ \t]
[:cntrl:]	[\x00-\x1F\x7F]
[:print:]	[\x20-\x7E]
[:punct:]	[][!"#$%&'()*+,./:;<=>?@^_`{\
[:xdigit:]	[A-Fa-f0-9]

Présentation des expressions régulières¶

Il existe de nombreux sites Web permettant de pratiquer les compétences en expression régulière en ligne, tels que :

Author: tianci li