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Terminal

Intermediate Terminal

  • file type that exists as pointer, a reference to another file

    • when you alter teh original file, you also alter all of the links

  • since we have files and folders located all over the file system, it becomes difficult to identify where many of these are located. Fortunately, we can create a link (aka as alias) to a file or folder using the ln command.

    • ln <path-to-link> <name-of-link>

  • physical copy that stays sync'd to original unless original deleted

  • there are two kinds of links we can make, hard & symbolic links

  • hard links are carbon copy of file that is linked

  • will automatically update or sync when linked file has any changes made

  • duplicate of the original file

    • both are a pro & con

      • pro: stays sync'd

      • con: because takes up as much room in memory as original

    • stays up to date with original

    • if original deleted, the hard linked file persists regardless

    • if move original file, the linked file persists regardless

  • reference to file

  • if original file deleted or moved, the link is broken

  • doesn't take up same space in memory as original file

  • to create a symbolic link, we use the -s flag

    • ln -s <path-to-link> <name-of-link>

  • creates a pointer back to the original

  • delete or move original file the link breaks

  • can symlink to a directory, hard links to a directory don't work

The Find Command

  • one fo the most useful terminal commands is the find command

  • to find a specific file in your current directory, you can simply type find and the name of the file. (If you try to find a folder you will find all of the contents inside as well)

find <exact match of what you are looking for>

  • to find something with a bit more complexity, use the following pattern:

  1. find

  2. a filepath

  3. an expression (this is when you have the most flexibility)

  • this is nice if we know exactly the name of the file we are looking for, but many times we need to use wildcard characters

  • here are some:

    • *: any number of characters

    • ?: one character

    • []: any of the characters inside the brackets

Examples:

  • find inside of some folder (assume we are inside that folder) anything that ends with .html

    • find . -name "*.html"

  • find inside of some folder (assume we are inside that folder) anything that ends with a three letter file extension

    • find . -name "*.???"

  • find inside of some folder (assume we are inside that folder) anything that starts with the letters f, t, or s

    • find . -name "[fts]*"

Grep

Grep Intro

  • search within files

  • stands for Global Regular Expression Print

  • i flag: case insensitive

  • A flag: display a certain number of lines after

  • v flag: invert pattern (you can think of this as anything NOT what you were searching for)

  • c flag: count the number of matches

  • n flag: show line number

  • w flag: characters in a row (word)

  • d flag: digit (0-9)

  • r flag: recursive (with out this grep cannot search through a directory)

  • .: current directory

Grep Regex

  • Regex (aka Regular Expression) are functions that search for a particular pattern in alphanumeric characters

  • Regex is used to define patterns in a string of characters

    • used to search a text for potential matches

  • Regex is common and quite powerful

    • use them to check whether a user has submitted a properly formatted email address or phone number

  • Wildcards

    • .: matches any character

      • Example: how many names have a full name that is four characters long?

        • grep -wc "..." names.txt

    • *: match zero or more of the preceding character or expression

      • Example: how many names start with a captial 'T'?

        • grep -wc "T.*" names.txt

    • []: any specific characters

      • Example: how many names start with a capital 'L', 'M' or 'E'?

        • `grep -wc "[L, M, E].*" names.txt``

    • [^]: do not match

      • Example: how many names do not start with a capital 'T'?

        • grep -wc "[^T].*" name.txt

    • \: escape character

      • Example: get all digits

        • grep '==\d' requirements.txt

      • Example: get all that begin with '==' & 1 digit

        • grep '==\d.' requirements.txt

Recursive Grep

  • find w/in multiple files w/in a directory

    • grep -ir 'bycrypt' .

Last modified: 10 March 2024
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