IT 1100 : Introduction to Operating Systems

Chapter 17 Searching for Files

Don't forget the Finding Things Exercises in Canvas.

Textbook Time

There are a lot more options for find in the book than we will use. So don't feel overwhelmed. Just focus on the power that find has.

Commands

• locate - find files by name. The locate command references an index compiled the night before, so the searches are very fast. The locate program performs a rapid database search of pathnames, and then outputs
  every name that matches a given substring.
  • The file has to be in the database in order for it to be found
  • example: locate bin/zip, can combine with grep to restrict rows shown
• The locate database is created by another program named updatedb. Usually, it is run periodically as a cron jobonce per day, if you create a file, it won't be detected by the locate command until this command has run.

Commands (find)

• find - search for files with a specific criteria. More powerful but more complex than locate. The search is done real time, so searches may take longer.
  • More examples:
    • find ~ -type f -name "*.JPG" -size +1M | wc -l #find by size, name
    • Can find by user, last modified time, permissions, more...

Commands (find)

• With find, you can also execute a particular action on the found file like so:
  • find ~ -type f -name 'foo*' -ok ls -l '{}' ';' or
  • find ~ -name 'foo*' -exec rm -rf {} \;

Commands (xargs)

• xargs - The xargs command in UNIX is a command line utility for building an execution pipeline from standard input. What does this mean??
  • What if you want to search through a bunch of files for a string
    • find . | xargs grep 'someline' vs. find . | grep 'someline'
  • Compare these two
    • find ./foo -type f -name "*.txt" -exec rm {} \;
    • find ./foo -type f -name "*.txt" | xargs rm
• touch - change file times or create new file
• stat - display file status

Examples

• locate /etc/res # will list files and directories in the /etc directory that start with res
• find /etc -type f # lists only files in the /etc directory that start with res
• find /etc/res* -type d # lists only directories in the /etc directory that start with res
• find ~ -type f -name "*.jpg" -size +1M # lists only files that end in .jpg and are greater than 1 MB in size
• find ~ -type f -name "*.jpg" -size +1M | xargs ls -l # xargs takes the output of the find command and lists it in an ls -l format