Untitled

• CS 288 Intensive Programming in Linux focuses on the Linux Command Line Interface

Linux Command Line Interface (CLI)

• The CLI is provided by a Linux shell.

• The shell is the first thing seen after logging into a server.

• The shell interacts and runs commands

• A variety of Linux shells exist, including bash, Bourne Shell (sh), C Shell, and tcsh.

help command

• The help command displays information about shell built-in commands and is useful when writing shell scripts
• Typing "help" or "help topic" provides a list or the help page for the specified topic
• Typing "help help" shows the help page for the help command

man command

• A manual displays information about the specified entity

• man chmod shows info about the chmod command

• Manual sections include:

• 1: Executable programs or shell commands (e.g., man 1 read)

• 2: System calls (functions provided by the kernel) (e.g., man 2 read)

• 3: Library calls (functions within program libraries) (e.g., man 3 read)

• 4: Special files (usually found in /dev)

• 5: File formats and conventions (e.g., /etc/passwd)

• Most manuals are available online

File Pathname

• Pathname refers to the location and name of a file.
• Root directory is represented by /, current directory by ., parent directory by .., and home directory by ~
• Absolute pathnames start from the root directory, e.g., $ cd /home/CS288/tom
• Relative pathnames are typically related to the current directory, e.g., $ cd ./hw/hw1 or $ cd ../hw2

Basic Commands

• ls lists files.
• cd changes directories
• pwd shows the current working directory
• mkdir makes a directory
• echo displays a line of text
• cat concatenates files and prints to standard output (e.g., $ cat a.txt b.txt)
• rmdir removes a directory
• rm removes files and directories. Use rm -r to remove directories and their contents recursively
• mv moves or renames a file
• cp copies a file
• date shows the current time
• time runs a program and reports execution time
• du shows the file size or space consumption
• locate, whereis, and which are used to find a file

File and Directory Information

• File and directory information displayed shows:
• type
• permissions
• number of hard links
• name
• size
• user & group
• last time of modification

File System Permissions

• Permissions for files include:
• Read access - read or copy a file
• Write access - write to the file, including deleting the file
• Execute access - execute programs and shell scripts that are text files containing Linux commands
• Permissions for directories include:
• Read access - list the contents of a directory
• Write access - create files
• Execute access - modify file permissions

Linux Permissions

• Permissions are set for the user, group, and others with a single digit from 0-7
• Read = 4
• Write = 2
• Execute = 1

chmod command

• Use the chmod command to set permissions
• chmod 755 myfile sets owner to rwx, group to r-x and other to r-x
• Owner = 111
• Group = 101
• Other = 101
• chmod 540 myfile sets owner to r-x, group to r--, other to ---
• Owner = 101
• Group 100
• Other = 000
• chmod 744 myfile sets owner to rwx, group to r--, other to r--

Redirecting

• > and >> change the standard output to a file, with > overwriting and >> appending
• cmd > filename
• < changes the standard input to a command
• cmd < file.txt
• | changes standard input and output to another program
• cmd1 | cmd 2

Multiple Commands

• Commands separated by operators:
• ; executes commands sequentially
• && executes the second command only if the first command is successful (returns an exit status of zero).
• || executes the second command only if the first command fails (returns a non-zero exit status).

cat command

• The cat command copies the input to output unchanged and concatenates specified file names to stdout
• -n numbers output lines starting from 1

Linux Utility Conventions

• POSIX recommends conventions for command-line arguments
• Programs are implemented via getopt()
• man and help describes command synopses following them
• Arguments are options if the begin with a hyphen (-) delimiter
• Option names are single alphanumeric characters
• Multiple options may follow a hyphen delimiter in a single token if they do not take arguments

head command

• The head command displays the first few lines of a specified file
• head [-number] [filename...]
• -number sets the number of lines to display, defaulting to 10
• filename... is the list of filenames to display
• When more than one filename is specified, the start of each file's listing will display the filename

tail command

• The tail command displays the last part of a file
• tail -n [+|-]number [filename]
• tail [+|-]number [filename]
• +number begins copying a the specified number away from the beginning of the file
• -number, or number begins from end of file if not specified, the number defaults to 10

cut Command

• The cut command helps to select columns and filter parts of input lines
• can select columns
• can select a range of character positions
• Some options include
• -f listOfCols: prints only the specified columns with tab-separated output
• -c listofPos: prints only chars in the specified positions
• d c use character c as the column separator
• Lists are specified as ranges (e.g. 1-5) or comma-separated (e.g. 2,4,5).

paste Command

• The paste command displays multiple text files side by side
• If the inputs are files a, b, c, then the first line of output is composed of the respective first lines of a, b, and c
• Each file is separated by a tab character
• If files are a different length, output keeps outputting data from the largest file with empty strings for the smaller files

sort Command

• The sort command copies input and ensures the output is arranged in ascending order of lines
• Can sort based on dictionary order or numeric order
• Can specify the key used in the sort with flexibility
• The default key is the entire line

Syntaxes

• sort [options] filename Options
• -n Numeric order, sort by arithmetic value
• -d Dictionary order
• -t Specify delimiter
• -k Key
• -r Sort in reverse order
• -o filename Write output to filename

The -k Tag

• key: -k [start_position][,stop_position]
  • start_position and stop_position both begin from 1 and are inclusive
    • If stop_position is omitted, stop_position defaults to line's end by default
• Formation of each position: f[.c][options]
  • f is a field number, c is a character position in the field
  • options: one or more single-letter ordering options
  • dictionary? Numeric? Reverse? override global ordering options
• There can be multiple keys
• 3-k4n

uniq Command

• The uniq command deletes repeated lines in a file
• uniq [ -cdu] [input-file] [ output-file]
  • -d Writes only the duplicated lines
  • -u Writes only those lines that are not duplicated
  • -c Supersedes the -u/-d options and each line in the output is proceded by an occurence count
• The default output is the union (combination) of the command

wc Command

• The wc command counts the number of lines, characters or words
• Options:
  • -l counts the number of lines
  • -w counts the number of words
  • -c counts the number of characters
• The default is to count lines, words and characters

tr Command

• The tr command translates or deletes characters
• tr [OPTION]... SET1 [SET2] performs text transformations, such as uppercase to lowercase, repeat squeezing, deleting specific characters, find and replacing characters
  • -c first complement SET1
  • -d deletes characters
  • -s squeezes repeats

Vi Editor

• Vi editor is fast and easy
• Basic modes are edit and command
  • 'esc' is used for command mode
  • 'i, a' is used for edit mode (insert or append mode)
• Other commands used with colon- :q,:w,:q!,:e
  • :q quits
  • :w write
  • q! quits without saving
  • :e open another file for editing
  • :wq write and quit
• Searching uses '/'
  • In command mode, '/' finds the specified word you want to search
  • Press n for forward search and N for backward search
• A specific line can be jumped to by typing the line number followed by shift + G
• Search and replace by typing :%s/this/that - will search string "this" and replace with 'that'