Searching for Files or Content

find

find command is used to search for files and directories, and even perform operations on the files/directories found.

find [path] [expression]

• [path]: specifies the directory to start the search from. If path is not specified, the current directory is used as the starting point.

• [expression]: specifies the search criteria. expression can contain one or more tests and actions. Tests are used to match files based on different criteria, while actions are used to perform operations on the matched files.

  1. match options:

  • -name pattern: matches files based on their name. The pattern argument can be a string or a regular expression.

    # The pattern can include wildcards such as * and ?.
    find . -name "*.txt"

  • -type type: matches files based on their type. The type argument can be f for regular files, d for directories, l for symbolic links, and more.

    # searches for all directories 
    # in the current directory and its subdirectories
    find . -type d

  • -size size: matches files based on their size. The size argument can be a number followed by a size suffix, such as k for kilobytes, M for megabytes, and so on.

    # searches for all files that are more than 1 megabyte in size
    find . -type f -size +1M

  • -mtime days: matches files based on their modification time. The days argument specifies the number of days ago the file was modified.

    # searches for all files that were modified more than 30 days ago
    find . -type f -mtime +30

  • -user user: matches files based on their owner. The user argument specifies the username of the file owner.

    # Find all files in the /home directory 
    # that are owned by the user john
    find /home -user john
  2. action options:

  • -exec command {} \;: performs a command on the matched files. The {} placeholder is replaced by the name of the matched file or directory, and \; marks the end of the command.

    # print the size of each file with the extension .txt
    find . -name "*.txt" -exec du -sh {} \;

  • -print: displays the files that are found by the find command.

    find . -type f -name "*.txt" -print

  • -delete: deletes the files that are found by the find command.

    find . -type f -name "*.log" -delete

grep

grep is short for global regular expression print. It's used to search for a specified pattern of text in one or more files or standard input.

grep [options] pattern [file...]

• pattern: regular expression (or string) that you want to search for in the specified file(s), or in standard input if no file is provided.

• file: the file or files that you want to search in.

  # allows searching in multiple files
  grep apple fruits.txt vegetables.txt

• options: optional command-line arguments that can modify the behavior of grep.

Commonly used options:

• --include: restricts the grep search to only certain types of files.
  For example, you can use --include="*.txt" to only search through those files and ignore all other files.

• --exclude: specifies a filename pattern that should be excluded from the grep search.

  # syntax:
  grep [OPTIONS] PATTERN --include=GLOB_PATTERN FILE_PATTERN
  
  # search for the word "example" in all .txt files
  grep --include='*.txt' -r 'example' .
  
  # search for the word "example" in all .txt and .md files
  grep --include='*.txt' --include='*.md' -r 'example' .
  备注

  If --include is not used, all files in the specified directories and subdirectories will be searched through. --include helps narrow down the search.

• -i: ignores case.

• -v: inverts the match, i.e., selects non-matching lines.

• -n : displays the matched lines and their line numbers.

  • -A n: prints searched line and n lines after the result.
  • -B n: prints searched line and n line before the result.
  • -C n: prints searched line and n lines after before the result.

• -w: matches the whole word.

• -r: searches recursively through directories and their subdirectories.

  # include all subdirectories in a search
  grep -r pattern *

• -e expression: specifies the pattern to search for. Can be used multiple times.

  # lines that contain either pattern1 or pattern2 in file.txt
  grep -e pattern1 -e pattern2 file.txt

• -c: prints only a count of matching lines.

• -l: prints only the list of filenames only.

• -f file: takes patterns from a file, one pattern per line.

Using find and grep in conjunction

To search for specific content in specific files, you can use find and grep in conjuction as follows:

find /path/to/search -name "*.txt" -exec grep "search_pattern" {} \;

This command:

1. searches for all .txt files in /path/to/search.
2. searches for the text string search_pattern within each of those files.

Performing Operations on the Searched Files/Content

You can use find and grep to search for what you want, but eventually you might want to perform operations on what is searched.

To pass the searched results to the operation command, use | to pipe the output of grep to the operation command.

sed

Replaces all old_string with new_string in the searched content.

find /path/to/search -name "*.txt" -exec grep "search_pattern" {} \; | sed 's/old_string/new_string/g'