18.2. Globbing. Comtrol DeviceMaster Software Development Kit

Advanced Bash-Scripting Guide

18.2. Globbing

Bash itself cannot recognize Regular Expressions. Inside scripts, it is commands and utilities -- such as sed

and awk -- that interpret RE's.

Bash does carry out filename expansion [100] -- a process known as globbing -- but this does not use the standard RE set. Instead, globbing recognizes and expands wild cards. Globbing interprets the standard wild

card characters [101] -- * and ?, character lists in square brackets, and certain other special characters (such as

^ for negating the sense of a match). There are important limitations on wild card characters in globbing, however. Strings containing

*

will not match filenames that start with a dot, as, for example,

.bashrc

. [102]

Likewise, the

?

has a different meaning in globbing than as part of an RE.

bash$

ls -l

total 2

-rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 a.1

-rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 b.1

-rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 c.1

-rw-rw-r-- 1 bozo bozo 466 Aug 6 17:48 t2.sh

-rw-rw-r-- 1 bozo bozo 758 Jul 30 09:02 test1.txt

bash$

ls -l t?.sh

-rw-rw-r-- 1 bozo bozo 466 Aug 6 17:48 t2.sh

bash$

ls -l [ab]*

-rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 a.1

-rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 b.1

bash$

ls -l [a-c]*

-rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 a.1

-rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 b.1

-rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 c.1

bash$

ls -l [^ab]*

-rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 c.1

-rw-rw-r-- 1 bozo bozo 466 Aug 6 17:48 t2.sh

-rw-rw-r-- 1 bozo bozo 758 Jul 30 09:02 test1.txt

bash$

ls -l {b*,c*,*est*}

-rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 b.1

-rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 c.1

-rw-rw-r-- 1 bozo bozo 758 Jul 30 09:02 test1.txt

Bash performs filename expansion on unquoted command-line arguments. The echo command demonstrates

this.

bash$

echo *

a.1 b.1 c.1 t2.sh test1.txt

bash$

echo t*

t2.sh test1.txt

bash$

echo t?.sh

t2.sh

Chapter 18. Regular Expressions 357

Advanced Bash-Scripting Guide

It is possible to modify the way Bash interprets special characters in globbing. A set -f command disables globbing, and the

nocaseglob

and

nullglob

options to shopt change globbing behavior.

See also Example 11-5.

Filenames with embedded whitespace can cause globbing to choke. David Wheeler shows how to avoid

many such pitfalls.

IFS="$(printf '\n\t')" # Remove space.

# Correct glob use:

# Always use for-loop, prefix glob, check if exists file.

for file in ./* ; do # Use ./* ... NEVER bare *

if [ -e "$file" ] ; then # Check whether file exists.

COMMAND ... "$file" ...

fi done

# This example taken from David Wheeler's site, with permission.

Chapter 18. Regular Expressions 358