Bash Basics Archive

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List all the files from /etc containing the pattern 127.0.0.1.
Only print the lines containing your username and root in the file /etc/passwd (only one grep

should be used)

In the bash man-page read the part related to redirections. Explain the following operators >, >>, <<<, >&1, and 2>&1 >. What is the use of the tee command.

>: Redirect output to specified file, rewrite this file.
>>: Redirect output to specified file, append to the end of it.
<<<: Redirect input using specified file as source, stop when a line containing a specified word is seen. The specification will be expanded using ~ expansion, parameter expansion and variable expansion.
>&1: Redirect the output to stdout.
2>&1 >: Redirect the content of stderr to stdout.
tee: Reads from stdin and write to stdout and files. This is often used within a pipe, writing results to files.

xargs: Constructs commands and execute. Used to execute commands (especially with those only taking input from stdin) on a list of arguments.
|: The pipe. Redirects the output of the command before it to the input of the command behind it.

What are the head and tail commands? How to “live display” a file as new lines are appended?

ps: Report a snapshot of processes running in system.
top: Display real-time view of processes and their information. (htop does this with better visualization)
free: Report a snapshot of memory/swap status of the system.
vmstat: Report virtual memory statistics such as processes, memory status, etc.

sh: The original default shell in Unix systems.
csh: The C shell, with features such as aliases, command histor and so.
bash: Created by the GNU Project, the default shell in most Linux Distributions today.
zsh: The Z shell, contains features of bash, but also has additional features such as spell checking.

They are positional arguments for shell scripting. ${N} stands for the N-th argument for a command, while ! in bash is expanded as the process ID of the most recently executed command and ? is executed as the exit status of the last executed command.

The PS3 variable is used to select inside a script. Without using this variable the default #? fpr select command will be displayed.
Example:

iconv is used to convert some text from one encoding to another. It is useful when handling files with different encoding due to different localization.

Given a variable $temp, what is the effect of ${#temp}, ${temp%%word}, ${temp/pattern/string}.

${#temp}: Length of this variable.
${temp%%word}: Content of $temp excluding the longest pattern matching word.
${temp/pattern/string}: Content of $temp, replacing matches of pattern by string.

Search online (not on the man pages), how files are organized on a Unix like system. In particular explain what are the following directories used for:

/: The root directory.
/lib: Libraries as dependency for the binary files in /bin.
/usr/lib: Libraries as dependency for the binary files in /usr/bin.
/srv: Data for services provided by the system.
/sbin: Executables for administrative purposes.
/bin: Binary executables, including essential tools such as ls, cp, ...
/mnt: Filesystem mount points for physical storages, remote/virtual filesystems, etc.
/usr/src: Source files that are system related.
/media: Default mount point for removable devices such as USB storage.
/dev: Mount points for peripheral devices as a file representation.
/boot: Files required for system booting process.
/usr/bin: Binary executables distributed with the system but not residing in /bin.
/proc: Virtual filesystem with runtime system information.
/opt: Reserved directory for softwares and other packages that are not of the default installation of the system distribution.
/vmlinuz: The compressed Linux kernel executable that is bootable.
/etc: Configuration files for the system.
/usr/share: Architecture independent data files of a given OS.
/sys: Interface to the kernel providing filesystem-like view of kernel information/configuration.
/var: A place for variable files (usually ) such as system logs.
/initrd.img: Link to the latest installed Linux initial RAM disk.
zp: Zero-padding, you know.

Write a game where the computer selects a random number, prompts the user for a number, compares it to its number and displays “Larger” or “Smaller” to the user, until the player discovers the random number initially chosen by the computer.