C-Shell

A custom Unix-like shell implemented in C, supporting command execution, process management, directory navigation, logging, piping, redirection, and several built-in utilities.

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Overview

C-Shell is a feature-rich shell designed to mimic and extend the behavior of standard Unix shells. It supports both built-in and external commands, advanced process management (foreground/background), command history, colored directory listings, piping, redirection, and custom utilities like hop, reveal, seek, proclore, log, and more.

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Features and Functionalities

• Command Execution: Run both built-in and external commands.
• Foreground/Background Processes: Launch and manage jobs in the foreground or background.
• Process Management: Bring jobs to foreground/background, kill jobs, and view running/stopped jobs.
• Directory Navigation: Use hop to change directories, including shortcuts for home and previous directories.
• Colored Directory Listing: Use reveal for ls-like listings with color coding and detailed info.
• File/Directory Search: Use seek to search for files/directories recursively with flexible flags.
• Command Logging: All commands (including erroneous ones) are logged to log_file.txt in the home directory.
• Command History: View, purge, or execute previous commands using the log command.
• Piping and Redirection: Support for |, <, >, and >> operators.
• Signal Handling: Handles Ctrl+C (SIGINT), Ctrl+Z (SIGTSTP), and child process signals.
• Custom Utilities:
  • proclore: View process details.
  • neonate: Monitor the most recently created process.
  • iMan: Fetch online man pages.
  • activities: List all jobs started by the shell.
  • ping: Send signals to processes.
• Alias and Custom Functions: Support for aliases and shell functions via myshrc.
• ANSI Color Support: Colorful prompts and outputs for better readability.

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Available Commands

Built-in Commands

• hop [dir] ...
  Change directory. Supports ~, -, relative, and absolute paths.
• reveal [-a] [-l] [path]
  List directory contents with color and optional details.
• seek [-d] [-f] [-e] <name> [dir]
  Search for files/directories recursively.
• proclore [pid]
  Show process info for the shell or a given PID.
• log [purge|execute <index>]
  Show, purge, or execute from command history.
• activities
  List all jobs started by the shell.
• fg <pid>
  Bring a background job to the foreground.
• bg <pid>
  Resume a stopped job in the background.
• neonate -n <seconds>
  Monitor the most recently created process.
• ping <pid> <signal>
  Send a signal to a process.
• iMan <command>
  Fetch and display the online man page for a command.

External Commands

• Any valid system command (e.g., ls, cat, sleep, etc.) can be executed.

Operators

• ; — Command separator.
• | — Pipe output of one command to another.
• <, >, >> — Input/output redirection.

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Usage

Compilation

make
./a.out

Prompt

The shell prompt displays as:

<username@system:~>

Example Commands

hop ~/Documents
reveal -la
seek -f -e main.c ~
log
log execute 2
sleep 5 &
activities
fg 12345
bg 12345
proclore
proclore 12345
neonate -n 2
iMan ls

Redirection and Piping

reveal -l > files.txt
cat files.txt | grep main
hop .. | wc

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Configuration

Aliases and Functions

You can define aliases and shell functions in the myshrc file:

alias reveall="reveal -l"
alias home="hop ~"

mk_hop() {
    if [ -z "$1" ]; then
        echo "Usage: mk_hop <directory>"
        return 1
    fi
    mkdir -p "$1"
    hop "$1"
}

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Notes and Limitations

• The maximum input size is 5000 characters (#define SIZ 5000).
• Directory listing supports up to 1024 files per directory.
• Backgrounding for pipes is not supported.
• Some advanced shell features (like echo i>file text) are not handled.
• ANSI color codes will appear in redirected output files.
• Sometimes, you may need to press Ctrl+D multiple times to exit the shell.
• When a background command is brought to the foreground and runs for more than 2 seconds, the prompt will display the command and its duration.
• All commands, including errors, are logged in log_file.txt in the home directory.

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Existing README Content

Makefile Execution

• I created a Makefile, and it should be executed by running:

  make
  ./a.out

• I took the maximum input size as 5000 and declared it as SIZ (macro):

  #define SIZ 5000

Specifications

Spec-3

• If the first command is:

  hop t1 -

  The previous directory is defined as the path to t1.

Spec-4

• If reveal - is performed but there are no previous directories, it prints an error like this:

  opendir: No such file or directory

• The number of files (all executables, files, and folders) a directory can have is:

  #define MAX_FILES 1024

• If the -l flag is present in the input command, the color coding reflects only on the file or directory name.

Spec-5

• Erroneous commands are also stored.
• A file called log_file.txt is created in the home directory (where the shell is invoked) and all the commands are stored in it:

  FILE *log_file = fopen("log_file.txt", "a");
  if (log_file != NULL) {
      fprintf(log_file, "%s\n", command);
      fclose(log_file);
  }

Spec-6

• If there are multiple sleep commands like:

  sleep 3; sleep 5

  They are displayed as:

  <JohnDoe@SYS:~ sleep : 3 sleep 5: 8s>
  

• Background processes are not handled for the implemented commands like hop, reveal, etc.

Spec-7

• Virtual memory is measured in kilobytes.

Spec-10

• If a command’s output is redirected to newfile.txt but the command results in an error, the error is printed in newfile.txt. For example:

  hop -

  Results in:

  OLDPWD not set
  

  Being written to newfile.txt.
• Cases like:

  echo i>newfile.txt text

  Are not handled.
• When a command like:

  reveal -la > a.txt

  Is executed, the ANSI color codes used will appear in the output file.

Spec-11

• When a command like:

  hop ..|wc

  Is executed, it will not hop to the parent directory.
• However:

  hop .. > a.txt

  Will hop to the parent directory.
• Invalid use of pipes is reported as:

  Invalid use of pipe
  

• The commands in a pipeline are run sequentially.

Spec-12

• Backgrounding for pipes does not work.
• Commands like:

  echo "Hi" & > a.txt

  Are not valid in this shell.

Spec-14

• Sometimes, you may need to press Ctrl+D 2 or 3 times if the shell does not log out immediately (kills all processes and logs out of the shell).

Spec-15

• When a background command is brought to the foreground, if its execution takes more than 2 seconds (e.g., sleep 20 running in the background is brought to the foreground using fg), the prompt will display:

  sleep : [ts]
  

• If sleep x is running and Ctrl+D is encountered, the shell logs out after the execution of sleep x.

Spec-16

• If the -n flag is not used, the shell prints the usage:

  Usage: neonate -n [time_arg]\n
  

• The case where n=0 is not handled.

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