Linux Command One Liners - Exercise

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• To empty a file or truncate a file to 0 size
• To replace content of a file
• To append content to a file as a new line
• To append content to a file without new line (by continuing last line )
• To append content to a file 
• To read first line of a file and store it in a variable 
• To read a file line by line and store it in a variable
• To read random line from a file and store it in a variable
• To read only 3 columns/fields form a file into variables
• To find number of lines, words, characters in a file and store it in a variable
• To find value in 2nd and 5th column of a one line variable and store it in a variable
• To find size of file and store it in a variable
• To make a copy of file
• To move or rename a file
• To generate Small letter a to z (with spaces between characters)
• To generate Capital letter A to Z (with spaces between characters)
• To generate Small letter a to z (without spaces between characters)
• To generate Capital letter A to Z (without spaces between characters)
• To generate all letters in a column output and store it in a variable
• To generate numbers from 1 to 100 (with spaces between numbers)
• To generate numbers from 1 to 100 (in column format)
• To generate numbers 0 to 9 with a leading zero as pad
• To generate n number of words 
• To generate alphanumeric strings
• To generate 5 copies of the same string
• To join two strings/variables
• To Split a string on a given character
• To replace only first occurrence of string 
• To replace only all occurrences of string 
• To find the length of the string
• To extract a substring from a string
• To uppercase a string
• To lowercase a string
• To redirect the standard output of a command to a file
• To redirect the standard error of a command to a file
• To redirect both standard output and error of a command to a file
• To discard standard output of a command to a file
• To discard standard error of a command to a file
• To discard standard output and error of a command to a file
• To redirect contents of a files to the standard input of a command 
• To redirect list of strings i.e. multiline to the standard input of a command 
• To redirect a single line of text to the standard input of a command 
• To redirect standard output of all command 
• To redirect standard error of all command 
• To redirect standard output and error of all command 
• To send the output from multiple commands to a file
• To use exec command in script to capture all standard error and standard output  in separate file 
• To prevent overwriting the contents of a file when redirecting output
• To redirect standard input to a file and print it to standard output
• To send standard output of one command to standard input of another command
• To send standard output and error of one command to standard input of another command
• How order of redirection matters
• To swap standard output and standard error
• To send standard output to one command and standard error to another command
• To find the exit codes of all piped commands
• To erase all shell history
• To stop logging history for this session
• To change log file for capturing command history 
• To add timestamp to history logs
• To show history
• To repeat last executed command
• To execute the most recent command starting with the given string
• To open the previous command you executed in a text editor
• Use short-keys on shell prompt to move to beginning of the line
• Use short-keys on shell prompt to move to end of the line
• Use short-keys on shell prompt to move the cursor “one word” backward
• Use short-keys on shell prompt to move the cursor “one word” forward
• Use short-keys on shell prompt to delete “last word”
• Use short-keys on shell prompt to undo recently deleted “last word”
• Use short-keys on shell prompt to move the cursor “one character” backward
• Use short-keys on shell prompt to move the cursor “one character” forward
• Use short-keys on shell prompt to delete “whole line”
• Use short-keys on shell prompt to search the history backward
• Use short-keys on shell prompt to search the history forward
• Use short-keys on shell prompt to swap “two adjacent characters” 
• Use short-keys on shell prompt to swap “two adjacent words” 
• Use short-keys on shell prompt to convert characters next to cursor location in a word to uppercase 
• Use short-keys on shell prompt to convert characters next to cursor location in a word to lowercase 
• Use short-keys on shell prompt to capitalized a character in a word
• Use short-keys on shell prompt to comment the current line (i.e. append # at the beginning quickly)
• Use short-keys on shell prompt to delete “one character” to the left
• Use short-keys on shell prompt to delete “one character” to the right
• Use short-keys on shell prompt to comment the current line (i.e. append # at the beginning quickly)
• Use short-keys on shell prompt to undo last action 
• Use short-keys on shell prompt to undo all changes to a line
• Use short-keys on shell prompt to clear screen
• To list CRON jobs for a user
• To edit CRON jobs for a user
• To schedule a job which will run every minute for capturing number of processes running for each user on system
• To schedule a job which will run on each 12 min for capturing number of open files on system for against each user 
• To schedule a job which will run hourly for capturing user’s logged in at that moment
• To schedule a job which will run twice in a day for checking filesystem utilization and through alert for utilization more than 40%
• To schedule a job which will run alternate day at 9 AM for backup of a directory by keeping latest 3 copies including current one
• To schedule a job which will run each alternate Sunday for calculating top 10 users having home directory usage high.
• To schedule a job which will run on first minute of each year to capture uptime of system
• To print date in terminal default format
• To print Date in terminal GMT/UTC time zone
• To set a date
• To display Month, Day and Year
• To display Hours, Minutes and Seconds
• To find the number of seconds from unix epoch.
• To display date with customized text
• To execute a job in the background and get it in foreground again (dependent on current session)
• To execute a job in the background and get it in foreground again (not dependent on current session)
• To display calendar of Sept, 1972 
• To display calendar of first three months of 2008
• To display calendar of complete year 1999
• To toggle between the last two directories cd -
• To go to home directory cd ~
• To check permissions summary for a folder i.e. list of possible users, group and permissions with count of each possibility

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