/Linux_Shell

Primary LanguageC

Linux Shell

Specification 1: Display requirement

When you execute your code a shell prompt of the following form must appear: <username@system_name:curr_dir> E.g. <Name@UBUNTU:~>

Specification 2: Builtin commands

  • cd : To change the current directory
  • pwd : Prints the current path
  • echo : Prints

Specification 3: ls command

Implement ls [al] – (it should be able to handle

  • ls
  • ls -l
  • ls -a
  • ls -la

Specification 4: System commands with and without arguments

All other commands are treated as system commands like : emacs, vi and so on. Foreground processes: For example, executing a "vi" command in the foreground implies that the shell will wait for this process to complete and regain control when this process exits. Background processes: Any command invoked with "&" is treated as background command. This implies that the shell will spawn that process and doesn't wait for the process to exit. It will keep taking user commands. E.g: <Name@UBUNTU:> ls & This command when finished, will print its result to stdout. <Name@UBUNTU:> emacs & <Name@UBUNTU:~> ls -l -a

Specification 5: pinfo command (user defined)

pinfo : prints the process related info of your shell program.

Specification 6: Foreground and background processes

Apart from the user defined commands, all other commands are treated as system commands like: emacs, vi and so on. Foreground processes: For example, executing a "vi" command in the foreground implies that your shell will wait for this process to complete and regain control when this process exits. Background processes: Any command invoked with "&" is treated as background command. E.g <NAME@UBUNTU:> ls & This command when finished, should print its result to stdout. <NAME@UBUNTU:> emacs & <NAME@UBUNTU:> ls -l -a <NAME@UBUNTU:> echo hello As and when emacs exits, your shell program should check the exit status of emacs and print it on stderr <NAME@UBUNTU:~> emacs with pid 456 exited normally

<NAME@UBUNTU:~>

Specification 7: Input-output redirection functionality

Output of running one (or more) commands must be redirected to a file. Similarly, a command might be prompted to read input data from a file and asked to write output to another file. E.g. Output redirection <NAME@UBUNTU:> diff file1.txt file2.txt > output.txt E.g. Input redirection <NAME@UBUNTU:> sort < lines.txt E.g. Input-Output redirection <NAME@UBUNTU:~> sort < lines.txt > sortedlines.txt Note: There is another clause for output direction '>>', and that must be implemented appropriately.

Specification 8: Implement command redirection using pipes

A pipe is identified by "|". One or more commands can be piped as the following examples show. E.g. Two Commands <NAME@UBUNTU:> more file.txt | wc E.g. Three commands <NAME@UBUNTU:> grep "new" temp.txt | cat - somefile.txt | wc

Specification 9: Implement I/O redirection + pipes redirection

E.g. <NAME@UBUNTU:> ls | grep *.txt > out.txt <NAME@UBUNTU:> cat < in.txt | wc -l > lines.txt

To run the code :

- Make file : 'make'
- Run the shell file : './shell'
- To clean, run 'make clean'