extglob – expression power of rgular expressions in bash/ksh

extglob

In addition to the traditional globs (supported by all Bourne-family shells) that we’ve seen so far, Bash (and Korn Shell) offers extended globs, which have the expressive power of regular expressions. Korn shell enables these by default; in Bash, you must run the command

shopt -s extglob

in your shell (or at the start of your script — see note on parsing below) to use them. The pattern matching reference describes the syntax, which is reproduced here:

?(pattern-list)
Matches zero or one occurrence of the given patterns.
*(pattern-list)
Matches zero or more occurrences of the given patterns.
+(pattern-list)
Matches one or more occurrences of the given patterns.
@(pattern-list)
Matches one of the given patterns.
!(pattern-list)
Matches anything except one of the given patterns.

Patterns in a list are separated by | characters.

Extended globs allow you to solve a number of problems which otherwise require a rather surprising amount of ugly hacking; for example,

# To remove all the files except ones matching *.jpg:
rm !(*.jpg)
# All except *.jpg and *.gif and *.png:
rm !(*.jpg|*.gif|*.png)
# To copy all the MP3 songs except one to your device
cp !(04*).mp3 /mnt

To use an extglob in a parameter expansion (this can also be done in one BASH statement with read):

# To trim leading and trailing whitespace from a variable
x=${x##+([[:space:]])}; x=${x%%+([[:space:]])}

Extended glob patterns can be nested, too.

[[ $fruit = @(ba*(na)|a+(p)le) ]] && echo 'Nice fruit'

Reference:  http://mywiki.wooledge.org/glob

 

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Author: rajukv

Hadoop(BigData) Architect and Hadoop Security Architect can design and build hadoop system to meet various data science projects.

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