CS 497C

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CS 497C Introduction to UNIXLecture 24 -
Simple Filters

• Chin-Chih Changchang_at_cs.twsu.edu

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comm What is Common?

• comm shows the lines that are common, and
  optionally shows you the lines unique to either
  or both files.
• When you run comm, it displays a three-columnar
  output. The first column contains lines unique to
  the first file, and the second column shows lines
  unique to the second file. The third column
  displays common lines to both files.

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comm What is Common?

• To drop a particular column, simply use its
  column number with the - sign.
• comm 3 foo12 selects lines not command to both
  files.
• comm -12 foo1 foo2 selects lines common to both
  files.

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head Displaying the Beginning of a File

• The head command displays the top of the file. It
  displays the first 10 lines when used without an
  option.
• To display the first N lines, use symbol
  followed by N.
• head -3 group
• To open last modified file for editing, use
• vi ls -t head -1

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tail Displaying the End of a File

• The tail command displays the end of the file. It
  displays the last 10 lines when used without
  arguments.
• To display last three lines, use
• tail -3 file
• Tail can also be used with a line number (with
  the k option) to start extraction from a
  specific line.
• tail 801 foo

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tail Displaying the End of a File

• To output the last 512 bytes, use
• tail -512c foo
• You can also use tail to monitor the growth of a
  file with the -f option.
• tail -f install.log

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cut Slitting a File Vertically

• The cut command is used to slice a file
  vertically.
• To extract the columns, use the -c (column)
  option followed by the column numbers
• cut -c1-4 /etc/group
• cut -c -3,6-22,55- foo
• 1-4 indicates column 1 to 4. -3 indicates column
  1 to 3. 55- indicates column 55 to the end of
  line.

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cut Slitting a File Vertically

• To cut fields, use the -d option for the
  delimiter and -f (field) option for specifying
  the field list. cut uses the tab as the default
  delimiter.
• This is how you cut out the first and third
  fields of the /etc/group file
• cut -d -f1,3 /etc/group
• cut can be used to extract the first word of a
  line by specifying the space as the delimiter.
• who cut -d -f1

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paste Pasting Files

• What you cut with cut can be pasted back with the
  paste command.
• paste also uses the d option to specify the
  delimiter, which by default is also the tab.
• We can use paste to literally join the two files
  calc.lst and result.lst.
• paste -d calc.lst result.lst
• paste is also a filter. We can use bc and paste
  in a pipeline
• bc lt calc.lst paste d calc.lst -