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This chapter is from the book

Searching and Editing Text Files

Search and edit text files by using the following commands.

  • grep: The grep command allows you to search inside a number of files for a particular search pattern and then print matching lines. For example, grep blah file will search for the text “blah” in the file and then print any matching lines.
  • sed: The sed (or Stream EDitor) command allows search and replace of a particular string in a file. For example, if you want to find the string “cat” and replace it with “dog” in a file named pets, type seds/cat/dog/g pets.

Both grep and sed are extremely powerful programs. There are many excellent tutorials available on using them, but here are a couple of good Web sites to get you started:

Five other commands are useful for dealing with text.

  • cat: The cat command, short for concatenate, is useful for viewing and adding to text files. The simple command cat FILENAME displays the contents of the file. Using cat FILENAME file adds the contents of the first file to the second and displays both on the screen, one after the other. You could also use cat file1 >> file2 to append the contents of file1 to the end of file2.
  • nano: Nano is a simple text editor for the command line. To open a file, use nano filename. Commands listed at the bottom of the screen are accessed via pressing Ctrl followed by the letter. To close and save a file you are working on, use Ctrl-X.
  • less: The less command is used for viewing text files as well as standard output. A common usage is to pipe another command through less to be able to see all the output, such as ls | less.
  • head: The head command is used for viewing the first 10 lines of text files as well as standard output. A common usage is to pipe another command through head to be able to see varying lines of output, such as ls | head.
  • tail: The tail command is used for viewing the last 10 lines of text files as well as standard output. A common usage is to pipe another command through tail to be able to see varying lines of output, such as ls | tail.
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