Searching For and Extracting Data

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grep

The grep command searches for files that contain a specified string and returns the name of the file and (if it’s a text file) the line containing that string.

• can also use to search a specified file for a specified string
• uses regular expressions
• if a filename is not specified, it uses standard input
• shell uses some characters for its own purposes, so you may need to enclose regex in quotes
  • e.g., | or *

find

The find command locates files using filename and file’s date stamps by searching through a specified directory tree.

• tends to be slow because of the brute-force approach
• can use multiple directory paths

wc

wc provides basic word statistics on text files.

• e.g., wc newfile.txt
  • outputs: 37 59 1990 newfile.txt
  • 37 lines
  • 59 words
  • 1,990 bytes

cut

The cut command extracts text from fields in a file record.

• frequently used to extract variable information from a file whose contents are highly patterned
• to use:
  • pass to it one or more options that specify what information you want
  • followed by one or more filenames

sort

The sort command sorts information in a file.

• sorts alphabetically by default with no options
• e.g.,

$ sort pets.txt
bird
cat
dog
fish

• no changes are made to the files data, only output is sorted

cat

The cat command displays text files on screen and can concatenate files together.

• files themself are not modified, only output