Linux Commands Cheatsheet

Note: Replace <placeholder> with appropriate file-name or command option/s.

• whoami: to display the username of the currently logged-in user.
• passwd: to change the user’s password.
• man <command>: to display the manual pages of a command and their available options.
  • To search for a specific keyword inside the man page, press ‘/’ key followed by the keyword.
• type <command>: to display the information about command type.
• <command> --help: to find documentation for those commands whose man pages do not exist.
• pwd: to print the path of the current working directory starting frorm the root.
• ls: to list the contents (files and folders) of a directory.
• ls -a or ls --all: to list all the contents of a directory including the hidden contents.
• ls -l: to list the contents of a directory in long listing format.
• cd: to change the current working directory in the terminal.
• cd ..: to move one level up from current working directory into the parent directory.

  Note: In linux, ‘~’ (tilde character) is used to represent the current user’s home directory, and ‘/’ (forward slash) is used to represent the user’s root directory.

• echo <message>: to display text or output to terminal.
• touch <file.txt>: to create new empty files or to update the access and modification date to current time if the file already exists.
• file <fileName>: to determine the file type of a specified file.
• mkdir <newDirectoryName>: to create a new working directory.
• nano <fileName>: to open a file in the text editor from the terminal.
• nano +[lineNumber] <fileName>: to open the file at a specific line.
• rm <fileName>: to remove/ delete a file.
• rm -d <folderName>: to delete an empty folders.
• rm -r <folderName>: to delete non-empty folders.
  • Tip: “-i” (iterative) option can be used to confirm the deleteion of files and folders. It also works with nested directories.
• mv <source> <destination>: to move a file/files and directories from one location to another.
• mv <currentName> <newName>: to rename the files and folders.
• cp <source> <destination>: to create copies of files and folders/directories.
• cat <file1> [<file2>]: to read the contents of a file and print them out.
• tac <fileName>: to print the contents of a file in reverse, i.e. the last line in the file will be printed first and so on.
• rev <fileName>: to print the contents of a file in reverse order “horizontally”. Ex. “abc” will be printed as “cba”.
• less <fileName>: to display the contents of a file one page at a time. (Use ‘f’ and ‘b’ keys to go one page forward or backward. Alternatively “up” and “down” arrow keys can be used to scroll by one line.)
• head <fileName>: to print the first 10 lines of a file.
• head -n <fileName>: to print first n lines of a file.
• head -c <fileName>: to print ‘c’ bytes of data from the specified file.
• tail <fileName>: to print the last 10 lines of the file.

  Note: “-n” and “-c” options also work with “tail” command.

• wc <fileName>: to print no. of lines, words and characters present in a file.
• wc -l <fileName>: to print the no. of lines of a file.
• wc -w <fileName>: to print total words in a file.
• sort <fileName>: to sort the contents of a file alphabetically.
• sort -r <fileName>: to sort the contents of a file alphabetically, but in reverse order.
• sort -n <fileName>: to sort numbers based on their numerical values rather than the character order.
• sort -u <fileName>: to sort only unique values and ignore duplicates.
• sort -k'n' <fileName>: to sort by field. ‘n’ denotes the coloumn number that needs to be sorted. It can also be used with numeric values by using the appropriate options.
• history: to display the previously executed shell commands in the order they were executed. To reuse the command without typing it again, we can reference its number with ‘!’ symbol. Ex. !420.
• tr: to translate, delete or merge characters or words. Refer the man page of explore all the options of ‘tr’ command.
• tee: to redirect output of the command to both, terminal (standard ouput) and file simultaneously.
• locate <fileName/ Path>: to quickly locate files and directories on the system. locate command uses pre-generated database for searching.
  • Useful options often used with locate command: 1) ‘-i’ to ignore the casing. 2) ‘-l’ or ‘–limit’ to limit the number of entries that locate retrives. 3) ‘-e’ prints only the entries that are present at the time locate is run.
• sudo updatedb: to update the database used by locate command.
• find: to list all the files and folders in the present directory.
• find <filePath>/: to find files and folders by path.
• find -type f: to search and list only the regular files within the current directory and its sub-directories.
• find -type d: to search and list for directories within the current directory and its sub-directories.
• find -name "<fileName>" to search for a file with a specific pattern.
  • -i option can be used with -name option to avoid casing.
• find -size ±<fileSize>: to find files with a specific file size. We can search for exact file size or use ‘+’ or ‘-‘ symbols to specify a range of values. Ex. find -size +20M will list all the files whose sizes are greater than 20 MB.
• find -user <Username>: to search for files and directories owned by specific user.

  Note: All the options mentioned above for find command can be combined together to further narrow down the search and get more specific results.

• Commonly used find options to filter the results based on time are:
  • -amin n: to find files that were last accessed (when the file was last read or opened). n minutes ago. We can specify +n for “greater than n minutes ago” and -n for “less than n minutes ago”.
  • -mmin n: to find files that were last modified (when the content of the file was last modified) n minutes ago.
  • -cmin n: to find files that were last changed (when the file was last modified or had its attributes changed) n minutes ago.
• find -exec {} ;: to execute a specified command on each file or item found by the find command. Ex. find -name "broken*" -exec rm '{}' ';' will delete all the files that start with “broken” in the file name.
  • Note: We need to wrap the {} and ; in quotes because those characters have special meanings otherwise.
• xargs: xargs reads items from standard input, separated by blanks (spaces or newlines) and then executes a command using those items.
  • Ex. echo "Folder1" "Folder2" | mkdir will give an error as mkdir expects us to pass arguments and not standard inputs. Instead we can use echo "Folder1" "Folder2" | xargs mkdir command, which will create two directories “Folder1” and “Folder2”.
• grep <PATTERN> <FILENAME>: to search and filter text based on the pattern provided within a file. Ex. grep "indigo" colors.txt will return all the instances of “indigo” inside the ‘colors.txt’ file.
  • Commonly used ‘grep’ options:
    • i: to make the search case insensitive.
    • -w: to ensure that ‘grep’ only matches words, rather than fragments locate inside of other words. Ex. grep -w "ate" random.txt will only match the word “ate” and not “donate”, “abbreviate”, etc.
    • -r: to perform a recursive search which will include all files under a directory, subdirectories and their files.
    • -c: to count and display the number of lines that match the specified pattern.
    • -m<num>: to limit the number of lines/matches ‘grep’ command will return. -m5 will display 5 results at max.
    • -n: to display line numbers along with matching lines when searching for a pattern in a specific file.
    • -o: to display only the matches instead of printing out the entire line containing each match.
    • A<n>: to display matching lines as well as n lines immediately following each matching line.
    • B<n>: to display matching lines as well as n lines preceding each matching line.
    • C<n>: to show matching lines as well as display n lines before and after each matching line.
• We can provide rexular expressions to grep. Rexular expressions helps us match complex patterns. The syntax for the same is as follows:
  • . - matches any single character.
  • ^ - matches the start of a line.
  • $ - matches the end of a line.
  • [abc] - matches any character in the set.
  • [^abc] - matches any char NOT in set.
  • [A-Z] - matches characters in a range.
  • * - repeat previous expression 0 or more times.
  • \ - escape meta-characters.

    Note: -E option must be used to enable the use of extended rexular expressions when specifying search patterns.

• ps -aux: to display list of all the running tasks in Unix/ Unix-Like Operating Systems.
• su - <usename>: to switch to another user’s account. It initates a new login session with specified user’s environment and privilexes.
• chmod <mode> <fileName>: to change the permissions (read/write/execute) of a file and directory.
  • Shorthand notations used with the chmod command to specify the catexory of users (owner, group, others, or all) for whom permissions are being modified are:
    • u - User (the owner of the file).
    • g - Group (members of the group a file belongs to).
    • o - Others (users who do not come under the catexory of user or group).
    • a - All of the above.
  • Notations to specify how permissions should be modified for a file or directory are:
    • + - Grants the permissions.
    • - - Removes/ Revokes the permissions.
    • = - Set a permission and remove others.
  • Notations to specify different types of permissions that can be assigned to files and directories are:
    • r - ‘Read’ permission.
    • w - ‘Write’ permission.
    • x - ‘Execute’ permission.
  • Ex. chmod g+w <fileName>: Grants ‘write’ permission to the ‘group’.
• Chmod also supports another way of representing permission patterns using octal numbers (base 8): |Octal| Binary|File Mode| |—–|——-|———| |0|000|—| |1|001|–x| |2|010|-w-| |3|011|-wx| |4|100|r–| |5|101|r-x| |6|110|rw-| |7|111|rwx|
  • Ex. chmod 664 <fileName> sets the permissions as -rw-rw-r–.
• sudo: to allow authorized users to execute commands with the privileges of the superuser (root).
• sudo -l: to list the permissions and privileges granted to the current user or a specific user.
• chown <username> <fileName>: to change the owner of a file or directory.
• chown :<groupName> <fileName>: to change the group owner of a file.
• chown <username>:<groupName> <fileName>: to change the owner and group owner of a file at the same time.
• groups <username>: to display the names of the groups to which a particular user belongs to.
• addgroup <groupName>: to create new groups.
• adduser <username> <groupName>: to add user to a group.
• printenv: to display the current environment vriables.
• export <Variable_name>=<value>: to set environment variables within a shell session. Ex. export hello="Hello World!
• unset <Variable_name>: to remove environment variable or shell variable. Ex. unset hello
• source <fileName>: to execute contents of a file in current shell or to refresh the environment variables. Ex. source ~/.bashrc
• alias <command_name>=<command>: to create custom commands for frequently used or longer commands. Ex. alias ll='ls -l'
• unalias <alias_name>: to remove or delete aliases that were previously defined using alias command. Ex. unalias ll

  Note: aliases are usually written inside .bashrc file but can also be written in a separate file named .bash_aliases inside the home directory (~).

• which <command_name>: to locate and display the path of an executable file associated with a given command. Ex. which ls
• crontab -e: to edit the user’s crontab file in unix/unix-like operating systems. The crontab file contains a list of scheduled tasks (cron jobs) that are executed at specified times or intervals.
  • Crontab syntax is as follows: |a|b|c|d|e|command| |-|-|-|-|-|——-| |Minute|Hour|Day|Month|Day (of week)|| |0-59|0-23|1-31|1-12|0-6 (starting from sunday)|
  • Ex. 30 * * * * <command> will run the command at exactly 30th minute of every hour.
  • Cron Characters:
    • * - Any Value.
    • 5,6 - List of values (5 and 6).
    • 1-4 - Range of values (1 to 4).
    • */5 - Step values (every 5).
• ps: to view a list of all the running processes.
  • Options to modify the output of ps command are:
    • -a - Lists processes from all users.
    • -u - Provides more detailed information, including the username of the process owner.
    • -x - Shows processes that are not associated with a terminal.
• du: to see the disk space usage of files and directories.
  • Commonly used options with du command are:
    • -h or --human-readable: Displays sizes in a human-readable format (ex. MB, KB, etc.)
    • -s or -summarize: Displays only the total disk usage of each specified directory, rather than listing individual subdirectories.
    • -c or --total: Provides total of disk usage for all specified directories.