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Linux Commands

Linux file globbing

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Introduction

The shell is also responsible for file globbing (or dynamic filename generation). In this session, we have covered the Linux file globbing.

asterisk(*)

The asterisk * is interpreted by the shell as a sign to generate filenames, matching the asterisk to any combination of characters (even none). When no path is given, the shell will use filenames in the current directory. See the man page of glob(7) for more information. (This is part of LPI topic 1.103.3.)

datasoft @ datasoft-linux ~$ ls
ABC.png                             part1
ajax-php-mysql-user-interface.html  part2
count                               part3
Desktop                             Pictures
Documents                           png
Downloads                           Public
examples.desktop                    sqlite3
file2                               sqlite-amalgamation-3080500 (2)
FileA                               sqlite-amalgamation-3080500.zip
FileB                               sqlite-shell-linux-x86-3080500.zip
linux-command-past-date.png         summer.png
mno.txt                             Summer.png
Music                               Templates
MyDir                               test1
MyDir1                              test2
MyDirA                              text2
Myfile1.doc                         typescript
MYFILE1.doc                         Untitled 1.odt
MYFILE2.doc                         Videos
MyTest                              xyz.txt
datasoft @ datasoft-linux ~$
datasoft @ datasoft-linux ~$ ls File*
FileA  FileB
datasoft @ datasoft-linux ~$ ls file*
file2
datasoft @ datasoft-linux ~$ ls *ext2
text2
datasoft @ datasoft-linux ~$ ls M*
Myfile1.doc  MYFILE1.doc  MYFILE2.doc

Music:

MyDir:
otherstuff  stuff  test  test2

MyDir1:
file1  file2  FileA

MyDirA:
FileA

MyTest:
file1  file1~  file2  FileA
 datasoft @ datasoft-linux ~$ 

question mark(?)

Similar to the asterisk, the question mark ? is interpreted by the shell as a sign to generate filenames, matching the question mark with exactly one character.

datasoft @ datasoft-linux ~$ ls
ABC.png                             part1
ajax-php-mysql-user-interface.html  part2
count                               part3
Desktop                             Pictures
Documents                           png
Downloads                           Public
examples.desktop                    sqlite3
file2                               sqlite-amalgamation-3080500 (2)
FileA                               sqlite-amalgamation-3080500.zip
FileB                               sqlite-shell-linux-x86-3080500.zip
linux-command-past-date.png         summer.png
mno.txt                             Summer.png
Music                               Templates
MyDir                               test1
MyDir1                              test2
MyDirA                              text2
Myfile1.doc                         typescript
MYFILE1.doc                         Untitled 1.odt
MYFILE2.doc                         Videos
MyTest                              xyz.txt
 datasoft @ datasoft-linux ~$ ls File?
FileA  FileB
 datasoft @ datasoft-linux ~$ ls Fil??
FileA  FileB
 datasoft @ datasoft-linux ~$ ls Fi???
FileA  FileB
 datasoft @ datasoft-linux ~$ 

square brackets ( [] )

The square bracket [ is interpreted by the shell as a sign to generate filenames, matching any of the characters between [ and the first subsequent ]. The order in this list between the brackets is not important. Each pair of brackets is replaced by exactly one character.

You can also exclude characters from a list between square brackets with the exclamation mark !. And you are allowed to make combinations of these wild cards.

 datasoft @ datasoft-linux ~$ ls
ABC.png                             part1
ajax-php-mysql-user-interface.html  part2
count                               part3
Desktop                             Pictures
Documents                           png
Downloads                           Public
examples.desktop                    sqlite3
file2                               sqlite-amalgamation-3080500 (2)
FileA                               sqlite-amalgamation-3080500.zip
FileB                               sqlite-shell-linux-x86-3080500.zip
linux-command-past-date.png         summer.png
mno.txt                             Summer.png
Music                               Templates
MyDir                               test1
MyDir1                              test2
MyDirA                              text2
Myfile1.doc                         typescript
MYFILE1.doc                         Untitled 1.odt
MYFILE2.doc                         Videos
MyTest                              xyz.txt
 datasoft @ datasoft-linux ~$ ls File[5A]
FileA
 datasoft @ datasoft-linux ~$ ls file [a5][Z!]
bash: !]: event not found
 datasoft @ datasoft-linux ~$ ls file[!3]*
file2
 datasoft @ datasoft-linux ~$ ls test[!3]*
test1

test2:
apti  test2  test2.txt

a-z and 0-9 ranges

The bash shell will also understand ranges of characters between brackets.

datasoft @ datasoft-linux ~$ ls
ABC.png         ajax-php-mysql-user-interface.html
Desktop         count
Documents       examples.desktop
Downloads       file2
FileA           linux-command-past-date.png
FileB           mno.txt
MYFILE1.doc     part1
MYFILE2.doc     part2
Music           part3
MyDir           png
MyDir1          sqlite-amalgamation-3080500 (2)
MyDirA          sqlite-amalgamation-3080500.zip
MyTest          sqlite-shell-linux-x86-3080500.zip
Myfile1.doc     sqlite3
Pictures        summer.png
Public          test1
Summer.png      test2
Templates       text2
Untitled 1.odt  typescript
Videos          xyz.txt
 datasoft @ datasoft-linux ~$ ls file [a-z]*
ls: cannot access file: No such file or directory
ajax-php-mysql-user-interface.html  png
count                               sqlite-amalgamation-3080500.zip
examples.desktop                    sqlite-shell-linux-x86-3080500.zip
file2                               summer.png
linux-command-past-date.png         test1
mno.txt                             text2
part1                               typescript
part2                               xyz.txt
part3

sqlite-amalgamation-3080500 (2):
shell.c  sqlite3.c  sqlite3.h  sqlite3ext.h

sqlite3:
sqlite-autoconf-3080500  sqlite-autoconf-3080500.tar.gz

test2:
apti  test2  test2.txt
 datasoft @ datasoft-linux ~$ ls file[0-9]
file2
 datasoft @ datasoft-linux ~$

$LANG and square brackets

But, don't forget the influence of the LANG variable. Some languages include lower case letters in an upper case range (and vice versa).

datasoft @ datasoft-linux ~$ ls [A-Z]ile?
file2  FileA  FileB
 datasoft @ datasoft-linux ~$ ls [a-z]ile?
file2  FileA  FileB
 datasoft @ datasoft-linux ~$ echo $LANG 
en_IN
 datasoft @ datasoft-linux ~$ LANG=C
 datasoft @ datasoft-linux ~$ echo $LANG
C
 datasoft @ datasoft-linux ~$ ls [a-z]ile?
file2
 datasoft @ datasoft-linux ~$ ls [A-Z]ile?
FileA  FileB
 datasoft @ datasoft-linux ~$ 

If $LC_ALL is set, then this will also need to be reset to prevent file globbing.

preventing file globbing

The screenshot below should be no surprise. The echo * will echo a * when in an empty directory. And it will echo the names of all files when the directory is not empty.

 datasoft @ datasoft-linux ~$ mkdir test10
 datasoft @ datasoft-linux ~$ cd test10
 datasoft @ datasoft-linux ~/test10$ echo *
*
 datasoft @ datasoft-linux ~/test10$ touch file10 file25
 datasoft @ datasoft-linux ~/test10$ echo *
file10 file25
 datasoft @ datasoft-linux ~/test10$

Globbing can be prevented using quotes or by escaping the special characters, as shown in this screenshot.

datasoft @ datasoft-linux ~/test10$ echo *
file10 file25
 datasoft @ datasoft-linux ~/test10$ echo \*
*
 datasoft @ datasoft-linux ~/test10$ echo '*'
*
 datasoft @ datasoft-linux ~/test10$ echo "*"
*
 datasoft @ datasoft-linux ~/test10$
  

Exercise, Practice and Solution :

1. Create a test directory and enter it.

Code:

mkdir testdir; cd testdir

2. Create files file1 file10 file11 file2 File2 File3 file33 fileAB filea fileA fileAAA file( file
2 (the last one has 6 characters including a space)

Code:

touch file1 file10 file11 file2 File2 File3
touch file33 fileAB filea fileA fileAAA
touch "file("
touch "file 2"

3. List (with ls) all files starting with file

Code:

ls file*

4. List (with ls) all files starting with File

Code:

ls File* 

5. List (with ls) all files starting with file and ending in a number.

Code:

ls file*[0-9]

6. List (with ls) all files starting with file and ending with a letter

Code:

ls file*[a-z]

7. List (with ls) all files starting with File and having a digit as the fifth character.

Code:

ls File[0-9]*

8. List (with ls) all files starting with File and having a digit as a fifth character and nothing else.

Code:

ls File[0-9]

9. List (with ls) all files starting with a letter and ending in a number.

Code:

ls [a-z]*[0-9]

10. List (with ls) all files that have exactly five characters.

Code:

ls ?????

11. List (with ls) all files that start with f or F and end with 3 or A.

Code:

ls [fF]*[3A]

12. List (with ls) all files that start with f have i or R as second character and end in a number.

Code:

ls f[iR]*[0-9]

13.List all files that do not start with the letter F.

Code:

ls [!F]*

14. Copy the value of $LANG to $MyLANG.

Code:

MyLANG=$LANG

15. Show the influence of $LANG in listing A-Z or a-z ranges.

Code:

see example in book

16. You receive information that one of your servers was cracked, the cracker probably
replaced the ls command. You know that the echo command is safe to use. Can echo replace
ls ? How can you list the files in the current directory with echo ?

Code:

echo *

17. Is there another command besides cd to change directories ?

Code:

pushd popd


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