BCCS199_Session_10

Question 1

In Linux (like Unix before it), nearly all configuration information is stored in…?

Answer 1

text files.
Contrast this with Windows, which stores configuration information in a huge, monolithic database called The Registry.
Text files are generally easier to set up and work with.
Linux includes a rich set of tools for viewing and editing text files. The following chapters describe some of these.

Question 2

cut command…?

Answer 2

selects columns of text in a text file.

Question 3

Commands like head, tail, and grep can be considered to make…?

Answer 3

“horizontal” cuts in a file.

Question 4

cut can be considered to make…?

Answer 4

“vertical” cuts in a file.

Question 5

Switches for the cut command…?

Answer 5

• Select character columns with the –c switch.
• Select fields with the –f switch.
• Select bytes with the –b switch (essentially the same as –c in most circumstances).
• Specify the field delimiter character with the –d switch (tab is default).

Example on slide 5 to 6

Question 6

Paste command…?

Answer 6

Appends files horizontally, line by line

See example on slide 7

Question 7

The diff command…?

Answer 7

Compares two files, and reports the differences between them.

See example on slide 8

Question 8

diff command line switches:

Answer 8

• c : Generate the context sensitive format
• C, –context[=N] Generate the context sensitive format, using N lines of context, if specified.
• u Generate the unified format.
• U, –unified[=N] Generate the unified format, using N lines of context, if specified.
• N Another format for specifying N lines of context. Only used with -c or -u.
• y, –side-by-side Generate the side by side format.
• W, –width=N Use N columns when generating side by side format.

–left-column Print only the left column when using the side by side format.

-q, –brief Only report if files differ, not the details on the difference.

Question 9

diff can be quite picky, and report all sorts of changes which are…?

Answer 9

trivial and ultimately meaningless. Here are some switches to ease the pain:

• b, -w, –ignore-all-space Ignore white space when comparing lines.
• B, –ignore-blank-lines Ignore white space when comparing lines.
• i, –ignore-case Ignore changes in case (i.e., consider upper and lower case characters equivalent.)
• I, –ignore-matching-lines=regex Ignore changes that insert or delete lines which match the mandatory argument regex.

Question 10

cut command…?

Answer 10

selects columns of text in a text file.

Question 11

Commands like head, tail, and grep can be considered to make…?

Answer 11

“horizontal” cuts in a file.

Question 12

cut can be considered to make…?

Answer 12

“vertical” cuts in a file.

Question 13

Switches for the cut command…?

Answer 13

• Select character columns with the –c switch.
• Select fields with the –f switch.
• Select bytes with the –b switch (essentially the same as –c in most circumstances).
• Specify the field delimiter character with the –d switch (tab is default).

Example on slide 5 to 6

Question 14

Paste command…?

Answer 14

Appends files horizontally, line by line

See example on slide 7

Question 15

The diff command…?

Answer 15

Compares two files, and reports the differences between them.

See example on slide 8

Question 16

diff command line switches:

Answer 16

• c : Generate the context sensitive format
• C, –context[=N] Generate the context sensitive format, using N lines of context, if specified.
• u Generate the unified format.
• U, –unified[=N] Generate the unified format, using N lines of context, if specified.
• N Another format for specifying N lines of context. Only used with -c or -u.
• y, –side-by-side Generate the side by side format.
• W, –width=N Use N columns when generating side by side format.

–left-column Print only the left column when using the side by side format.

-q, –brief Only report if files differ, not the details on the difference.

Question 17

diff can be quite picky, and report all sorts of changes which are…?

Answer 17

trivial and ultimately meaningless. Here are some switches to ease the pain:

• b, -w, –ignore-all-space Ignore white space when comparing lines.
• B, –ignore-blank-lines Ignore white space when comparing lines.
• i, –ignore-case Ignore changes in case (i.e., consider upper and lower case characters equivalent.)

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Question 18

The tr command…?

Answer 18

Performs character translations (substitutions, deletions, squeezing) on the input stream and passes the modified string to the output stream.

See example on slide 11

Question 19

See slide 12 for deleting characters examples

Answer 19

See slide 13 for squeezing characters

Question 20

aspell command is used for…?

Answer 20

spell checking text files.

Example on slide 14

Question 21

aspell can be used on the …?

Answer 21

stdin and stdout streams.

Question 22

aspell can also be used to start…?

Answer 22

an interactive spell check session (aspell - c filename)

This will highlight any word it can’t find in the dictionary in turn, and offer you a range of alternative for correction.

As usual, if there are no misspelled words, it says nothing at all.

Question 23

aspell two dictionaries are used by default…?

Answer 23

• The system-wide master dictionary in /usr/share/dict
• A user-specific dictionary stored in.aspell.en.pws
• A list of corrections made is kept in .aspell.en.prepl.
  Note: the .en. refers to English; other languages can be used as well.

Question 24

fmt command is generally used to…?

Answer 24

break long lines up into shorter ones by inserting newline characters.

Question 25

split comamnd is used to…?

Answer 25

split large files into a set of smaller files with a common prefix.

Question 26

Linux includes many commands for viewing, formatting, and manipulating text files.
This is useful, because…?

Answer 26

nearly all configuration information is stored in text files.
This rich set of text editing tools helps system administrators maintain their Linux system.