Jorge Saldívar

Tag: computer science

  • Linux Commands Cheat Sheet

    Here’s a list of common commands along with their descriptions and usage examples:

    1. ls – List Directory Contents
      • Usage: ls [options] [directory]
      • Example: ls -l /home (lists all files in /home with detailed information)
    2. cd – Change Directory
      • Usage: cd [directory]
      • Example: cd /home/user/Documents (changes the current directory to /home/user/Documents)
    3. pwd – Print Working Directory
      • Usage: pwd
      • Example: pwd (displays the path of the current directory)
    4. cat – Concatenate and Display Files
      • Usage: cat [options] [file]
      • Example: cat file.txt (displays the content of file.txt)
    5. cp – Copy Files and Directories
      • Usage: cp [options] source destination
      • Example: cp file1.txt file2.txt (copies file1.txt to file2.txt)
    6. mv – Move or Rename Files and Directories
      • Usage: mv [options] source destination
      • Example: mv file1.txt /home/user/Documents (moves file1.txt to /home/user/Documents)
    7. rm – Remove Files or Directories
      • Usage: rm [options] file
      • Example: rm file.txt (removes file.txt)
    8. mkdir – Create a New Directory
      • Usage: mkdir [options] directory
      • Example: mkdir new_folder (creates a new directory named new_folder)
    9. rmdir – Remove Empty Directories
      • Usage: rmdir [options] directory
      • Example: rmdir old_folder (removes the directory old_folder if it’s empty)
    10. grep – Search Text Using Patterns
      • Usage: grep [options] pattern [file]
      • Example: grep "hello" file.txt (searches for the word “hello” in file.txt)
    11. find – Search for Files in a Directory Hierarchy
      • Usage: find [path] [options] [expression]
      • Example: find /home -name "file.txt" (finds all files named “file.txt” in /home)
    12. chmod – Change File Modes or Access Control Lists
      • Usage: chmod [options] mode file
      • Example: chmod 755 script.sh (sets the permission of script.sh to 755)
    13. chown – Change File Owner and Group
      • Usage: chown [options] owner[:group] file
      • Example: chown user:group file.txt (changes the owner of file.txt to ‘user’ and the group to ‘group’)
    14. tail – Output the Last Part of Files
      • Usage: tail [options] [file]
      • Example: tail -n 5 file.txt (displays the last 5 lines of file.txt)
    15. head – Output the First Part of Files
      • Usage: head [options] [file]
      • Example: head -n 5 file.txt (displays the first 5 lines of file.txt)
    16. man – Interface to the System Reference Manuals
      • Usage: man [command]
      • Example: man ls (displays the manual page for the ls command)

    This is just a basic set of commands, and there are many more commands and options in Linux. For detailed information and more commands, you can always use the man command followed by the command name to read the manual pages.

    Linux Commands Cheat Sheet

  • Regex Cheat Sheet

    Simple Examples

    • hello: Matches the string “hello” exactly.
    • 123: Matches the string “123” exactly.
    • .: Matches any single character.
    • \d: Matches any digit character (0-9).
    • \w: Matches any word character (a-z, A-Z, 0-9, _).
    • \s: Matches any whitespace character (space, tab, newline).

    Examples

    • hello world: Matches the string “hello world” exactly.
    • hello|world: Matches either “hello” or “world”.
    • hello.*: Matches “hello” followed by zero or more characters.
    • hello\s: Matches “hello” followed by a whitespace character.
    • hello\d: Matches “hello” followed by a digit character.
    • hello\w: Matches “hello” followed by a word character.
    • hello\s\d: Matches “hello” followed by a whitespace character and a digit character.

    Quantifiers

    • a+: Matches one or more “a” characters.
    • a*: Matches zero or more “a” characters.
    • a?: Matches zero or one “a” character.
    • a{3}: Matches exactly three “a” characters.
    • a{3,}: Matches three or more “a” characters.
    • a{3,5}: Matches between three and five “a” characters.

    Character Classes

    • [abc]: Matches any of the characters “a”, “b”, or “c”.
    • [^abc]: Matches any character that is not “a”, “b”, or “c”.
    • [a-z]: Matches any lowercase letter.
    • [A-Z]: Matches any uppercase letter.
    • [0-9]: Matches any digit character.
    • [\w]: Matches any word character.
    • [\W]: Matches any non-word character.
    • [\s]: Matches any whitespace character.
    • [\S]: Matches any non-whitespace character.

    Anchors

    • ^hello: Matches “hello” at the beginning of a line.
    • world$: Matches “world” at the end of a line.
    • \bhello\b: Matches “hello” as a whole word.
    • \Bhello\B: Matches “hello” not as a whole word.

    Groups

    • (hello): Matches “hello” and captures it as a group.
    • (hello|world): Matches either “hello” or “world”.
    • (?:hello): Matches “hello” but does not capture it as a group.
    • (?=hello): Matches any string that is followed by “hello”.
    • (?!hello): Matches any string that is not followed by “hello”.

    Flags

    • /hello/i: Matches “hello” case-insensitively.
    • /hello/g: Matches all occurrences of “hello”.
    • /hello/m: Matches “hello” across multiple lines.
    • /hello/s: Matches “hello” across multiple lines and allows “.” to match newline characters.

    Special Characters

    • \: Escapes a special character.
    • .: Matches any single character except newline characters.
    • ^: Matches the beginning of a line.
    • $: Matches the end of a line.
    • *: Matches zero or more of the preceding character.
    • +: Matches one or more of the preceding character.
    • ?: Matches zero or one of the preceding character.
    • (: Begins a capturing group.
    • ): Ends a capturing group.
    • [: Begins a character class.
    • ]: Ends a character class.
    • {: Begins a quantifier.
    • }: Ends a quantifier.
    • |: Matches either the expression before or after the operator.
    • /: Begins and ends a regular expression.
    • i: Makes the regex case-insensitive.
    • g: Matches all occurrences of the pattern.
    • m: Makes the ^ and $ anchors match the beginning and end of lines.
    • s: Allows . to match newline characters.
    • \n: Matches a newline character.
    • \r: Matches a carriage return character.
    • \t: Matches a tab character.
    • \v: Matches a vertical tab character.
    • \0: Matches a null character (U+0000 NULL).
    • \xhh: Matches a character with the given hex code (e.g. \x0A matches a newline character).
    • \uhhhh: Matches a character with the given Unicode code point (e.g. \u0009 matches a tab character).
    • \cX: Matches a control character using caret notation (e.g. \cJ matches a newline character).
    • \u{hhhh}: Matches a character with the given Unicode code point (e.g. \u{0009} matches a tab character).

    Lookarounds

    • (?=hello): Positive lookahead. Matches any string that is followed by “hello”.
    • (?!hello): Negative lookahead. Matches any string that is not followed by “hello”.
    • (?<=hello): Positive lookbehind. Matches any string that is preceded by “hello”.
    • (?<!hello): Negative lookbehind. Matches any string that is not preceded by “hello”.

    Unicode Categories

    • \p{L}: Matches any letter character.
    • \p{M}: Matches any combining mark character.
    • \p{Z}: Matches any separator character.
    • \p{S}: Matches any symbol character.
    • \p{N}: Matches any number character.
    • \p{P}: Matches any punctuation character.
    • \p{C}: Matches any control character.
    • \p{Ll}: Matches any lowercase letter.
    • \p{Lu}: Matches any uppercase letter.
    • \p{Lt}: Matches any titlecase letter.
    • \p{L&}: Matches any letter character.
    • \p{Lm}: Matches any modifier letter.
    • \p{Lo}: Matches any other letter character.
    • \p{Mn}: Matches any non-spacing mark character.
    • \p{Mc}: Matches any spacing combining mark character.
    • \p{Me}: Matches any enclosing mark character.
    • \p{Zs}: Matches any space separator character.
    • \p{Zl}: Matches any line separator character.
    • \p{Zp}: Matches any paragraph separator character.
    • \p{Sm}: Matches any mathematical symbol character.
    • \p{Sc}: Matches any currency symbol character.
    • \p{Sk}: Matches any modifier symbol character.
    • \p{So}: Matches any other symbol character.
    • \p{Nd}: Matches any decimal digit character.
    • \p{Nl}: Matches any letter number character.
    • \p{No}: Matches any other number character.
    • \p{Pc}: Matches any connector punctuation character.
    • \p{Pd}: Matches any dash punctuation character.
    • \p{Ps}: Matches any open punctuation character.
    • \p{Pe}: Matches any close punctuation character.
    • \p{Pi}: Matches any initial punctuation character.
    • \p{Pf}: Matches any final punctuation character.
    • \p{Po}: Matches any other punctuation character.
    • \p{Cc}: Matches any control character.
    • \p{Cf}: Matches any format character.
    • \p{Cs}: Matches any surrogate character.
    • \p{Co}: Matches any private-use character.
    • \p{Cn}: Matches any unassigned code point.

    POSIX Classes

    • [:alnum:]: Matches any alphanumeric character.
    • [:alpha:]: Matches any alphabetic character.
    • [:ascii:]: Matches any ASCII character.
    • [:blank:]: Matches any whitespace character.
    • [:cntrl:]: Matches any control character.
    • [:digit:]: Matches any digit character.
    • [:graph:]: Matches any visible character.
    • [:lower:]: Matches any lowercase character.
    • [:print:]: Matches any printable character.
    • [:punct:]: Matches any punctuation character.
    • [:space:]: Matches any whitespace character.
    • [:upper:]: Matches any uppercase character.
    • [:word:]: Matches any word character.
    • [:xdigit:]: Matches any hexadecimal digit character.
    Regex Cheat Sheet