LPIC-1

Obtaining Text File Information

4 min read

1. wc (Word Count)

The wc command is used to count the number of lines, words, and bytes (or characters) in a text file. This is very useful when you need some basic statistics about a file’s content.

Basic Usage:

wc filename.txt

This will display three things by default:

  1. The number of lines
  2. The number of words
  3. The number of bytes (characters, including spaces)

Example Output:

15  100  1200 filename.txt

This means:

  • 15 lines in the file
  • 100 words in the file
  • 1200 bytes (characters) in the file

Variations of wc:

  • Lines Only (-l): To count only the number of lines in a file:

    wc -l filename.txt

  • Words Only (-w): To count only the number of words in a file:

    wc -w filename.txt

  • Bytes Only (-c): To count only the number of bytes (characters) in a file:

    wc -c filename.txt

  • Characters Only (-m): To count the number of characters (not bytes), use:

    wc -m filename.txt

  • Multiple Options: You can also combine options. For example, to count lines, words, and bytes:

    wc -l -w -c filename.txt

2. uniq — Display Unique Lines

The uniq command is used to filter out duplicate lines from a text file, showing only the unique lines. By default, uniq only works on consecutive duplicate lines.

Basic Usage:

uniq filename.txt

This command will display the file content but will remove any consecutive duplicate lines.

Example:

If filename.txt contains:

apple
banana
banana
cherry
apple

After running uniq, the output will be:

apple
banana
cherry
apple

Here, “banana” only appears once, as it was duplicated consecutively.

Variations of uniq:

  • -c (Count Occurrences): To show the number of occurrences of each unique line:

    uniq -c filename.txt

    Output:

    1 apple
2 banana
1 cherry
1 apple

    This shows how many times each unique line appears.

  • -d (Show Duplicate Lines Only): To display only the lines that appear more than once:

    uniq -d filename.txt

    Output:

    banana

  • -u (Show Unique Lines): To display only the lines that appear once:

    uniq -u filename.txt

    Output:

    apple
cherry

  • Sorting Before Using uniq: If the file is not sorted and you want uniq to work properly, you can combine it with sort. For example:

    sort filename.txt | uniq

3. nl — Add Line Numbers to a File

The nl command is used to add line numbers to a file’s content. It’s useful for viewing large files with line numbers, especially for debugging or references.

Basic Usage:

nl filename.txt

This will display the contents of filename.txt, but each line will be prefixed with a line number.

Example Output:

     1  apple
     2  banana
     3  cherry
     4  apple

Variations of nl:

  • Custom Line Number Format (-n): You can control how the line numbers are formatted with the -n option:

    • -n ln to left-align the line numbers:

      nl -n ln filename.txt

    • -n rz to add leading zeros for the line numbers:

      nl -n rz filename.txt

    • -n rn to right-align the numbers:

      nl -n rn filename.txt

  • Skipping Empty Lines (-s and -b): The -s option adds a separator between the line number and the line content, and the -b option controls how blank lines are numbered.

    For example, if you don’t want empty lines numbered, you can use:

    nl -b a filename.txt

  • Starting from a Specific Number (-v): You can start the line numbering from a specific number using the -v option:

    nl -v 100 filename.txt

    This will start numbering lines from 100.

Summary:

  • wc: Counts the number of lines, words, and bytes/characters in a file. You can specify which to count using options like -l, -w, -c.
  • uniq: Filters out duplicate lines, displaying only unique lines. You can show counts, duplicates, or unique lines only with options like -c, -d, -u.
  • nl: Adds line numbers to each line of a file for reference or debugging. You can control formatting, start from a custom number, and even skip blank lines.

Graph View