A Guide to Searching through the Command Line

locate

• The locate command performs a search of pathnames across our machine that match a given substring and then prints out any matching names.
• You have to install this command as it does not comes pre-installed
• It is nice and speedy because it uses a pre-generated database file rather than searching the entire machine.
• For example, locate chick will perform a search for all files that contain chick in their name
• It does not matter which directory you are in as you can locate folders which are in other directories
• The -i option tells locate to ignore casing
• The -l or --limit option will limit the number of entries to a number.

find

• The locate command is nice and easy, but it can only do so much! The find command is far more powerful! Unlike locate, find does not use a database file.
• By default, find on its own will list every single file and directory nested in our current working directory and also nested in the sub-directories.
• We can also provide a specific folder. find friends/ would print all the files and directories inside the friends directory (including nested folders)

• You can also find empty files by running find -empty

  Finding by Type

  • We can tell find to only find by file type: only print files, directories, symbolic links, etc using the -type option.
  • find -type f will limit the search to files
  • find -type d will limit the search to directories

  Finding by Name

  • We can provide a specific pattern for find to use when matching filenames and directories with the -name option. We need to enclose our pattern in quotes.
  • To find all files on our Desktop that end in the .txt extension, we could run find ~/Desktop -name "*.txt"
  • Use the -iname option for a case insensitive search

  Finding by Size

  • We can use the -size option to find files of a specific size. For example, to find all files larger than 1 gigabyte we could run find -size +1G
  • To find all files under 50 megabytes, we could run find -size -50M
  • To find all files that are exactly 20 kilobytes, we could run find -size 20k

  Finding by Time

  • mtime, or modification time, is when a file was last modified AKA when its contents last changed.
  • ctime, or change time, is when a file was last changed. This occurs anytime mtime changes but also when we rename a file, move it, or alter permissions.
  • atime, or access time, is updated when a file is read by an application or a command like cat.
  • We can use the -mtime num option to match files/folders that were last modified num*24 hours ago.
  • find -mmin -20 matches items that were modified LESS than 20 minutes ago.

  • find -mmin +60 matches items that were modified more than 60 minutes ago
    

    find -mmin -30
    

  • find -amin n will find files that were last accessed n minutes ago. We can specify +n for "greater than n minutes ago" and -n for "less than n minutes ago"

  • find -cmin -20 matches items that were changed LESS than 20 minutes ago.

  • find -cmin +60 matches items that were changed more than 60 minutes ago

  Logical Operators

  • We can also use the -and, -or, and -not operators to create more complex queries.
    

    find -type -f -not -name "*.html" # any file except .html
    

User-Defined Actions

• We can provide find with our own action to perform using each matching pathname.
• The syntax is find -exec command {} ;
• The {} are a placeholder for the current pathname (each match), and the semicolon is required to indicate the end of the command.

• To delete every file that starts with contains "broken" in its file name, we could run:
  

  find -name "*broken*" -exec rm '{}' ';'
  

  Note that we need to wrap the {} and ; in quotes because those characters have special meanings otherwise

xargs

• When we provide a command via -exec, that command is executed separately for every single element.

• We can instead use a special command called xargs to build up the input into a bundle that will be provided as an argument list to the next command.
  

  find -name "*.txt" -exec ls '{}' ';'
  find -name "*.txt" | xargs ls
  

• This example finds four individual chapter files (chapter1, chapter2, chapter3, and chapter4) and then passes them to the cat command, which then outputs the combined contents to a file called fullbook.txt.
  

  find -name "chapter[1-4].txt" | xargs cat > fullbook.txt
  

• xargs reads items from standard input, separated by blanks (spaces or newlines) and then executes a command using those items

• The mkdir command expects us to pass arguments. It doesn't work with standard input, so this example does NOT make any folders for us

• We can instead add in the xargs command, which will accept the standard input coming from echo and pass them as arguments to mkdir.
  

  echo "hello" "world" | mkdir # mkdir: missing operand
  echo "hello" "world" | xargs mkdir
  ls # hello world two folders made
  

Grep

• The grep command searches for patterns in each file's contents. Grep will print each line that matches a pattern we provide.

• For example, grep "chicken" animals.txt will print each line from the animals.txt file that contains the pattern "chicken"
  

  grep PATTERN FILE
  

• Use the -i option with grep to make the search case insensitive.

• grep -i "Chapter" book.txt will print all matching lines from the book.txt file that contain the word "chapter" in any casing.

• Use the -w option to ensure that grep only matches words, rather than fragments located inside of other words.

• grep -w "cat" book.txt would match cat but not catheter!

• Use the -r option to perform a recursive search which will include all files under a directory, subdirectories and their files, and so on.

• grep -r "chicken" will search the current working directory and any nested directories for lines that contain "chicken"

• The -c option tells grep to print the number of matches instead of printing the actual matches

• The -o option tells grep to only print out the matches, rather than the entire line containing each match.

• We can also provide regular expressions to grep by using the -E option