This is Lab Worksheet 4 - not an Assignment

This Lab Worksheet contains some practical examples that will prepare you to complete your Assignments.
You do not have to hand in this Lab Worksheet. Make sure you complete the separate Assignments on time. Quizzes and tests may refer to work done in this Lab Worksheet; save your answers.

Before you get started - REMEMBER TO READ ALL THE WORDS

You must have an account on the Course Linux Server to do this lab. Log in to the server and use the shell. Review the Class Notes related to this worksheet as you work through it. Leave your work on the Linux server. Do not delete any work from the Linux server until the term is over and your marks are complete!

Commands introduced and used in this Lab

• alias – (help alias) built-in bash command to create synonyms for command names.

• bash – Shell aliases

• bash – Shell wildcard (GLOB char) patterns: * ? [...] [!...]

• sum – generate a checksum

• unalias – remove an alias, or all aliases using -a

Log in to the Course Linux Server to do all commands in this lab. Set your bash PS1 shell prompt to show your login name, computer name, and the basename of your current directory, just as you did in the previous Lab. Leave your finished work on the server; do not delete it when you are finished the worksheet.

Using Wildcards (GLOB chars) in Pathname Specifications

Use the echo command to see how patterns expand first, before you use them in a real command line, e.g.

• echo /etc/pas* ; echo /dev/sd* ; echo /bin/*sh

WARNING: DO NOT USE LETTER RANGES: Do not use letter ranges separated by a dash, e.g. [a-z], without first understanding your system LOCALE setting. The dash range [a-z] often includes the upper-case letters from B through Z and may not include A. Using digits [0-9] is the only safe range allowed.

Use the echo command to see how GLOB patterns expand first, before you use them in a real command line:

$ echo /some/pattern* # echo the pattern on the screen before using the real command name!

$ rm /some/pattern* # now use the real command name with the verified pattern

Lab 4.1: Using ? to match any single character

As we do with most sections of each lab, we recursively remove and recreate a directory in which to do this section. This lets you return to this place and redo a section without having files left over from previous work.

[user@localhost ]$ cd ; rm -rf lab4.1 ; mkdir lab4.1 ; cd lab4.1

[user@localhost lab4.1]$ touch f1 f2 f3

[user@localhost lab4.1]$ touch f10 f20 f30

[user@localhost lab4.1]$ touch f11 f12 f13

[user@localhost lab4.1]$ touch f33 fffff

[user@localhost lab4.1]$ mkdir dir1 dir2 dir3

[user@localhost lab4.1]$ ls

dir1 dir2 dir3 f1 f10 f11 f12 f13 f2 f20 f3 f30 f33 fffff

[user@localhost lab4.1]$ ls | sum

33442 1 ( make sure you get this number, otherwise start over at the beginning of 4.1)

Use the echo command to see how patterns expand first, before you use them in a real command line.

[user@localhost lab4.1]$ cp f? dir1

1. Which files have been copied to the directory dir1? (First try to answer without typing the command.)

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[user@localhost lab4.1]$ cp f?0 dir2

2. Which files have been copied to the directory dir2? (First try to answer without typing the command.)

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[user@localhost lab4.1]$ cp f?3 dir3

3. Which files have been copied to the directory dir3? (First try to answer without typing the command.)

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[user@localhost lab4.1]$ echo ? ?? ?????

4. One of the above three patterns fails to expand to any pathname. Which pattern, and why?

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[user@localhost lab4.1]$ cp ? ?? ????? dir3

5. Why does the above command line give an error message from the copy command?

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[user@localhost lab4.1]$ ls /dev/tty*

6. The above command shows all terminal devices configured in your Linux system. Try it.
   What command line, similar to the above, shows only the five-character terminal device names,
   i.e. shows tty10 and tty63 and ttyS0, etc. but does not show tty or tty1 or tty9 etc.?

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Lab 4.2: Using * to match zero or more characters

This section depends on the files created at the start of the previous section. Create those files first.

[user@localhost lab4.1]$ cd ; rm -rf lab4.2 ; mkdir lab4.2 ; cd lab4.2

[user@localhost lab4.2]$ cp -a ../lab4.1/. . (note the single dot destination directory)

[user@localhost lab4.2]$ ls

dir1 dir2 dir3 f1 f10 f11 f12 f13 f2 f20 f3 f30 f33 fffff

[user@localhost lab4.2]$ ls | sum

33442 1 ( make sure you get this number, otherwise start over at the beginning of 4.1)

Use the echo command to see how patterns expand first, before you use them in a real command line.

[user@localhost lab4.2]$ rm dir?/* (clean out all files in these directories)

[user@localhost lab4.2]$ ls f*

1. What is the output of the last command, above? (First try to answer without typing the command.)

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[user@localhost lab4.2]$ ls -d d*

2. What is the output of the last command, above? (First try to answer without typing the command.)

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[user@localhost lab4.2]$ ls f*1 (that pattern contains a digit, not a letter)

3. What is the output of the last command, above? (First try to answer without typing the command.)

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[user@localhost lab4.2]$ ls -d *1 (that pattern contains a digit, not a letter)

4. What is the output of the last command, above? (First try to answer without typing the command.)

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[user@localhost lab4.2]$ ls -d *1* (that pattern contains a digit, not a letter)

5. What is the output of the last command, above? (First try to answer without typing the command.)

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Lab 4.3: Using [ ] to match a single character from a list of characters

Square brackets are shell metacharacters that indicate a GLOB pattern match for any one character in the list of characters between the square brackets. You can also match any one character that is not in the list by starting the list with an exclamation point !, e.g. [!abc] Circumflex is sometimes also allowed but doesn't work in all shells, so the exclamation point is preferred instead of using [^abc]

[user@localhost ]$ cd ; rm -rf lab4.3 ; mkdir lab4.3 ; cd lab4.3

[user@localhost lab4.3]$ touch hat help hit hot hut

[user@localhost lab4.3]$ ls | sum

07916 1 (make sure you get this number, otherwise start over at the beginning of 4.3)

Use the echo command to see how patterns expand first, before you use them in a real command line.

[user@localhost lab4.3]$ ls h[ao]t

6. What is the output of the last command, above? (First try to answer without typing the command.)

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[user@localhost lab4.3]$ ls h[aeiou]t

7. What is the output of the last command, above? (First try to answer without typing the command.)

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[user@localhost lab4.3]$ ls h[aeiou]*

8. Comparing with the previous output, which additional file is displayed? ___________________

9. Why? ______________________________________________________________________________

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[user@localhost lab4.3]$ cd ; rm -rf lab4.3b ; mkdir lab4.3b ; cd lab4.3b

[user@localhost lab4.3b]$ touch sda sdb sdc sdd

[user@localhost lab4.3b]$ touch sda1 sdb2 sdc3 sdd4

[user@localhost lab4.3b]$ ls | sum

61395 1 (make sure you get this number, otherwise start over at the beginning with rm above)

[user@localhost lab4.3b]$ ls sd[abc]

10. Which names are output by the last command, above? (First try to answer without typing the command.)

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[user@localhost lab4.3b]$ ls sda[1-4]

11. Which names are output by the last command, above? (First try to answer without typing the command.)

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[user@localhost lab4.3b]$ ls sd[bc][1-3]

12. Which names are output by the last command, above? (First try to answer without typing the command.)

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[user@localhost lab4.3b]$ echo sd[!ab][!12]

13. Which names are output by the last command, above? (First try to answer without typing the command.)

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List complements sometimes work using a leading circumflex, as [^abc], to mimic the behaviour of Regular Expressions, but the circumflex doesn't work in all shells so [!abc] is preferred in GLOB patterns.

Dashed character ranges [a-z] are not always predictable! Always test them first!

DO NOT USE DASHED RANGES: Do not use character ranges separated by a dash, especially alphabetic ranges, without first understanding your system LOCALE setting. The range [a-z] often includes the upper-case letters from B through Z and may not include A. Using only digits in the range, e.g. [0-9], may be safe.

The following shows the difference on two example Linux systems, depending on the LOCALE environment:

1. $ touch a A b B y Y z Z

2. server$ echo [a-z] # Server gives only lower-case: a b y z

3. server$ echo [A-Z] # Server gives only upper-case: A B Y Z

4. desktop$ echo [a-z] # Desktop gives an incomplete mix: a B b Y y Z z

5. desktop$ echo [A-Z] # Desktop gives an incomplete mix: A a B b Y y Z

The Server uses a traditional English-only LOCALE that expects only ASCII (English) characters where the Desktop uses a modern International LOCALE (e.g. LC_CTYPE=en_CA.utf8) that also includes Unicode characters in the range. Do not use dashed character ranges, especially alphabetic ranges, without first understanding your system LOCALE setting. Verify GLOB patterns using echo ! For a fuller explanation on Internationalization problems, including the use of POSIX character classes such as [:lower:] and [:upper:] read:

http://teaching.idallen.com/cst8177/15w/notes/000_character_sets.html

Lab 4.4: Using shell aliases

Aliases are built-in to your current shell. They are not separate commands like date and ls. Aliases let you define your own command names. You can also redefine existing command names and/or add your favourite options to existing command names. Many Linux systems come with some shell aliases defined already. These predefined aliases may be set in system RC files (under /etc) or in a .bashrc file placed into your account HOME directory. Know what aliases are set in your account before you start typing!

Listing all current shell aliases

[user@localhost ~]$ alias (list all current aliases - may be none)

1. In which man page are shell aliases documented? : ____________________________________

You can also use the help feature of your shell to get help on any built-in command, e.g. help alias

Creating a shell alias (for this shell only)

[user@localhost ~]$ alias myls='ls -alF --color=auto'

[user@localhost ~]$ alias
[user@localhost ~]$ ls .. (two dots - parent directory)

[user@localhost ~]$ myls .. (two dots - parent directory)

1. Describe how typing myls gives different output compared to typing ls:

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Removing a single shell alias (for this shell only)

[user@localhost ~]$ alias myls='ls -alF --color=auto'

[user@localhost ~]$ myls

[user@localhost ~]$ unalias myls

[user@localhost ~]$ alias

[user@localhost ~]$ myls

1. Record exactly the error message from using the undefined alias (undefined command name):

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Temporarily bypassing a current alias using backslash

Putting a backslash in front of a command name causes the shell to ignore any alias for that command.

[user@localhost ~]$ alias ls='ls -alF --color=auto'

[user@localhost ~]$ ls .. (two dots - parent directory)

[user@localhost ~]$ \ls .. (two dots - parent directory)

1. Describe how typing \ls gives different output compared to typing the aliased version of ls:

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2. Given what you see above, what is the function of the backslash character \ in front of an alias?

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3. Give a command to remove the ls alias: ________________________________________

4. What command will remove all current aliases (RTFM): _____________________________

5. Why doesn't man alias work? ____________________________________________________

Review: Basic Commands

1. How do mv and cp differ?

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2. Describe the purpose of the whoami command (read the man page):

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3. What is the purpose of the -i switch (option) to the ls command?

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4. What is the purpose of the -d switch (option) to the ls command?

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5. What command name and options copy an entire directory, including all the other files and sub-directories stored under it?

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6. What command name do you use to delete/remove an empty directory?

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7. What command name and options do you use to delete/remove a complete directory structure including all the other files and sub-directories stored under it?

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8. What command name and options would find any pathname ending in the basename of passwd, found in any directory, starting from the ROOT directory?

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9. What command name and options would find and print all the pathnames under the directory /etc?

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10. What command would find and print all the pathnames owned by the root user under /var/spool:

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11. How do you create a directory a/b/c/d/e including all the parent directories, in one command line?

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12. Rewrite the pathname /usr/./bin/../local/./bin/../sbin as a simple absolute pathname, without using any “.” or “..”:

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