BASIC CONCEPTS AND COMMANDS

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BASIC CONCEPTS AND COMMANDS

• Filters
• cut
• grep
• sort

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Filters

• Filter refers to any program that can take input
  from standard input, perform some operations on
  that input, and write the results to standard
  output.
• In other words, a filter is any program that can
  be used between two other programs in a pipeline.
• Eg. ls wc -l wc is a filter

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Filters

• Are head, tail, and sort filters?
• How about who, date, cd, pwd, echo, rm mv, cp?

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cut

• It is used to extract ( cut out ) various fields
  of data from a data file or the output a command.
• General format
  cut -cchars
  filename
• chars specifies what characters you want to
  extract from each line of file.

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cut

• Single character
• cut -c5 filename
• list of characters
• cut -c1, 4, 15, 40
  filename
• Range of characters
• cut -c10-30 filename
• from a character to the end of the line
• cut -c5- filename

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cut

• Cut can also read its input from std output.
• who cut -c1-8
• who cut -c10-16
• who cut -c1-8, 18-

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cut

• The -d and -f option are used with cut when you
  have data that is delimited by a particular
  character.
• Cut -ddchar -ffields filename
• dchar is the character that delimits each field
• fields specifies the fields to be extracted from

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cut

• Examples
• cut -d -f1 /etc/passwd
• cut -d -f1, 6 /etc/passwd
• If -d option is not supplied, the cut uses the
  tab character as the default field delimiter.
• To know in advance if fields are delimited by
  blanks or tabs, type the command
• sed -n 1 filename
• If the fields are separated by a tab, then a
  greater sign (gt) will be displayed.

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grep

• grep allows you to search one or more files for
  particular character patterns.
• grep pattern files
• every line of each file that contains pattern is
  displayed at the terminal.

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grep

• grep shell myfile
• grep John mylist
• grep shell

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grep

• Enclosing your grep pattern inside a pair of
  single quotes to protect it is a good idea.
• For example, to find all the lines containing
  asterisks inside the file stars, then typing
• grep stars
• does not work. Because shell substitutes the
  names of all files in your current directory.
• But try grep stars

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grep

• grep can also take its input from std input if no
  file name is specified.
• who grep ce144d04

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Task 1

• Using your regular expression knowledge, explain
  what each of the following grep command may
  display?
• grep tT filename
• grep A-Z filename
• grep 0-9 filename
• grep \.pic filename

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Task2

• Having a file with the following contents
• big
• bad
• bug
• bag
• bigger
• boogy
• What does grep b.g filename display?

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grep and options

• grep -i the filename
• ignores the case, display the, The, tHE, etc
• grep -v UNIX filename
• finds all the lines in the filename that dont
  contain the characters UNIX.
• Grep -l history .c
• displays list of file names that contain the
  pattern (not their actual lines).

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grep and options

• What do the following commands do?
• grep -l history .c wc -l
• grep history .c wc -l

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grep and options

• grep -n history filename.c
• places the line number before the lines that
  has been matched to contain that pattern.

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Sort

• Sort takes each line of the specified input file
  and sorts it into ascending order based on their
  ASCII value (Asciibetical order).
• Example sort names
• Alice
• Fred
• Fred
• Ralph

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Sort Options

• sort -u
• -u option tells sort to eliminate duplicate lines
  from the output
• sort -u names
• Alice
• Fred
• Ralph

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sort -r

• Use the -r option to reverse the order of the
  sort
• sort -r names
• Ralph
• Fred
• Fred
• Alice

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sort -o

• By default, sort writes the sorted data to
  standard output. To have it go into a file, you
  can use output redirection.
• sort names gt sorted_names
• Alternatively, you can use the -o option to
  specify the output file.
• sort names -o sorted_names

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sort -n

• The -n option to sort specifies that the first
  field to be considered a number, and the data is
  to be sorted arithmetically.
• Sort data sort -n data
• 14 2
• 2 3
• 23 14
• 3 23

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sort n (skipping fields)

• To sort your data file by the y value i.e., the
  second number on each line, use sort 1n to skip
  past the first number on the line. Compare
• sort -n data sort 1n data
• 2 11 14 6
• 3 33 2 11
• 14 27 23 27
• 23 6 3 33
• Note! 5n would mean to skip the first 5 fields.

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sort -t

• Generally sort assumes that the fields being
  skipped are delimited by space or tab characters.
  The -t option says otherwise.
• The character that follows the -t is taken as the
  delimiter character. Example
• sort /etc/passwd sorts the file by the first
  field (user name)
• sort 2n -t /etc/passwd sorts the file by
  the third colon-delimited field (user id).

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Filters

• Can you now add some other commands to your list
  of filters?

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