Linux Shell Commands Redirections & Wildcards

Challenge:

The primary challenge was mastering essential Linux shell functionalities to manipulate input, output, and error
streams, efficiently process text data, and use pattern matching (wildcards) for powerful file and command
management. This involved understanding how special shell characters control the flow of data between commands and
files in a command-line interface (CLI).

My Role & Actions:

I operated within a Linux environment to execute precise data flow and file pattern matching commands:

• Standard Output Redirection: Used the `>` operator to redirect the output of commands (`cal`, `date`) to a
  file, overwriting existing content.

• Output Appending: Employed the `>>` operator to add the output of a command (`date`) to the end of an
  existing file without deleting its contents.

• Error Redirection: Utilized the `2>` operator to specifically redirect standard error messages (e.g., from a
  failing `cut` operation on a nonexistent file) into a separate log file (`erreurs.log`).

• Stream Merging: Used the `2>&1` syntax to combine both standard output and standard error into a single
  destination file (`sio1.txt`).

• Piping & Filtering: Implemented pipelines (`|`) to chain commands together, using the output of one command
  as the input for the next. This was demonstrated using commands like `sort` and `tail` on system files
  (e.g.,
  `/etc/services`).

• Data Processing Chain: Executed a multi-step process using `cut`, `sort`, and `uniq` to extract a list of
  names from a CSV file, sort the resulting list, and eliminate duplicate entries (`avecdoublons` to
  `sansdoublons`).

• Wildcard Usage (Jokers): Demonstrated pattern matching using jokers like `*` (matching any sequence of
  characters), `?` (matching a single character), and character ranges (e.g., `[w-z]` or `[!a-v]`) within `ls`
  commands to select files based on criteria.

• Character Protection: Employed the backslash (`\`) and quotation marks (`’ ‘`, `” “`) to protect special
  shell characters (such as `#` or interpreting the variable `$HOME`) from being processed by the shell as
  commands or variables.

Solution & Outcome:

The practical work confirmed the ability to precisely control program output and input streams, a fundamental
requirement for efficient system administration and scripting. Successfully manipulating large text outputs (like
password files or service lists) using pipelines (`cut`, `sort`, `uniq`) proved command proficiency for data cleanup
and analysis. Furthermore, the correct application of wildcards demonstrated skill in rapidly locating and managing
files based on complex naming patterns, while protection characters ensured the integrity of file names containing
special symbols.

Key Skills Demonstrated:

• Linux Shell Scripting & Automation

• Input/Output Redirection (`>`, `>>`, `2>`, `2>&1`)

• Piping (`|`) and Text Filtering Utilities (`sort`, `cut`, `uniq`, `grep`)

• Wildcards and Pattern Matching

• Command-Line Interface (CLI) Proficiency.