Shell基礎筆記 - The Missing Semester of Your CS Education

可惜還是學生的時候不知道有這門好課，雖然已經有些經驗了，但還是想看看這門課能帶給我什麼新東西

快速複習

Basics of the Shell

• Shell = text-based interface for executing commands.
• Bash (Bourne Again Shell) is widely used.

Basic Commands

• date → Show current date/time
• echo hello → Print text to terminal
• echo $PATH → Show directories searched for commands
• which command → Locate the binary file of a command

Navigating the Filesystem

• pwd → Show current directory
• cd /path/to/dir → Change directory
• ls → List files
• ls -l → Show detailed file info
• cd .. → Move up one directory
• mkdir newdir → Create a directory

File Operations

• mv old new → Rename/move a file
• cp source dest → Copy a file
• rm file → Delete a file
• man command → Show manual for a command

Redirection & Pipes

• command > file → Redirect output to a file
• command >> file → Append output to a file
• command < file → Use file as input
• command1 | command2 → Pipe output of one command to another

Examples

• echo hello > hello.txt → Write “hello” to a file
• cat hello.txt → Display file contents
• ls -l / | tail -n1 → Show the last line of ls -l / output
• curl --head --silent google.com | grep -i content-length | cut -d ' ' -f2 → Get content length of a webpage

Running Commands as Root

• sudo command → Run command as superuser
• echo 3 | sudo tee /sys/class/backlight/thinkpad_screen/brightness → Change screen brightness
• tee displays program output and copying to a file

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Exercises

第五題

• 不能直接寫入，因為#是comment
• 不能用雙引號因為!是event
• 要用單引號或是\把驚嘆號轉換成字
• echo '#!/bin/sh' > semester
• echo "#\!/bin/sh" > semester

第九題

• 因為#!這行

第十題

• ./semester | grep last-modified > last-modified.txt