Linux Bash commands with definitions,
| adduser | Add a user to the system |
| addgroup | Add a group to the system |
| alias | Create an alias |
| apropos | Search Help manual pages (man -k) |
| apt-get | Search for and install software packages (Debian/Ubuntu) |
| aptitude | Search for and install software packages (Debian/Ubuntu) |
| aspell | Spell Checker |
| awk | Find and Replace text, database sort/validate/index |
| basename | Strip directory and suffix from filenames |
| bash | GNU Bourne-Again SHell |
| bc | Arbitrary precision calculator language |
| bg | Send to background |
| break | Exit from a loop |
| builtin | Run a shell builtin |
| bzip2 | Compress or decompress named file(s) |
| cal | Display a calendar |
| case | Conditionally perform a command |
| cat | Concatenate and print (display) the content of files |
| cd | Change Directory |
| cfdisk | Partition table manipulator for Linux |
| chgrp | Change group ownership |
| chmod | Change access permissions |
| chown | Change file owner and group |
| chroot | Run a command with a different root directory |
| chkconfig | System services (runlevel) |
| cksum | Print CRC checksum and byte counts |
| clear | Clear terminal screen |
| cmp | Compare two files |
| comm | Compare two sorted files line by line |
| command | Run a command - ignoring shell functions |
| continue | Resume the next iteration of a loop |
| cp | Copy one or more files to another location |
| cron | Daemon to execute scheduled commands |
| crontab | Schedule a command to run at a later time |
| csplit | Split a file into context-determined pieces |
| cut | Divide a file into several parts |
| date | Display or change the date & time |
| dc | Desk Calculator |
| dd | Convert and copy a file, write disk headers, boot records |
| ddrescue | Data recovery tool |
| declare | Declare variables and give them attributes |
| df | Display free disk space |
| diff | Display the differences between two files |
| diff3 | Show differences among three files |
| dig | DNS lookup |
| dir | Briefly list directory contents |
| dircolors | Colour setup for `ls' |
| dirname | Convert a full pathname to just a path |
| dirs | Display list of remembered directories |
| dmesg | Print kernel & driver messages |
| du | Estimate file space usage |
| echo | Display message on screen |
| egrep | Search file(s) for lines that match an extended expression |
| eject | Eject removable media |
| enable | Enable and disable builtin shell commands |
| env | Environment variables |
| ethtool | Ethernet card settings |
| eval | Evaluate several commands/arguments |
| exec | Execute a command |
| exit | Exit the shell |
| expect | Automate arbitrary applications accessed over a terminal |
| expand | Convert tabs to spaces |
| export | Set an environment variable |
| expr | Evaluate expressions |
| FALSE | Do nothing, unsuccessfully |
| fdformat | Low-level format a floppy disk |
| fdisk | Partition table manipulator for Linux |
| fg | Send job to foreground |
| fgrep | Search file(s) for lines that match a fixed string |
| file | Determine file type |
| find | Search for files that meet a desired criteria |
| fmt | Reformat paragraph text |
| fold | Wrap text to fit a specified width. |
| for | Expand words, and execute commands |
| format | Format disks or tapes |
| free | Display memory usage |
| fsck | File system consistency check and repair |
| ftp | File Transfer Protocol |
| function | Define Function Macros |
| fuser | Identify/kill the process that is accessing a file |
| gawk | Find and Replace text within file(s) |
| getopts | Parse positional parameters |
| grep | Search file(s) for lines that match a given pattern |
| groups | Print group names a user is in |
| gzip | Compress or decompress named file(s) |
| hash | Remember the full pathname of a name argument |
| head | Output the first part of file(s) |
| help | Display help for a built-in command |
| history | Command History |
| hostname | Print or set system name |
| iconv | Convert the character set of a file |
| id | Print user and group id's |
| if | Conditionally perform a command |
| ifconfig | Configure a network interface |
| ifdown | Stop a network interface |
| ifup | Start a network interface up |
| import | Capture an X server screen and save the image to file |
| install | Copy files and set attributes |
| jobs | List active jobs |
| join | Join lines on a common field |
| kill | Stop a process from running |
| killall | Kill processes by name |
| less | Display output one screen at a time |
| let | Perform arithmetic on shell variables |
| ln | Make links between files |
| local | Create variables |
| locate | Find files |
| logname | Print current login name |
| logout | Exit a login shell |
| look | Display lines beginning with a given string |
| lpc | Line printer control program |
| lpr | Off line print |
| lprint | Print a file |
| lprintd | Abort a print job |
| lprintq | List the print queue |
| lprm | Remove jobs from the print queue |
| ls | List information about file(s) |
| lsof | List open files |
| make | Recompile a group of programs |
| man | Help manual |
| mkdir | Create new folder(s) |
| mkfifo | Make FIFOs (named pipes) |
| mkisofs | Create an hybrid ISO9660/JOLIET/HFS filesystem |
| mknod | Make block or character special files |
| more | Display output one screen at a time |
| mount | Mount a file system |
| mtools | Manipulate MS-DOS files |
| mtr | Network diagnostics (traceroute/ping) |
| mv | Move or rename files or directories |
| mmv | Mass Move and rename (files) |
| netstat | Networking information |
| nice | Set the priority of a command or job |
| nl | Number lines and write files |
| nohup | Run a command immune to hangups |
| notify-send | Send desktop notifications |
| nslookup | Query Internet name servers interactively |
| open | Open a file in its default application |
| op | Operator access |
| passwd | Modify a user password |
| paste | Merge lines of files |
| pathchk | Check file name portability |
| ping | Test a network connection |
| pkill | Stop processes from running |
| popd | Restore the previous value of the current directory |
| pr | Prepare files for printing |
| printcap | Printer capability database |
| printenv | Print environment variables |
| printf | Format and print data |
| ps | Process status |
| pushd | Save and then change the current directory |
| pwd | Print Working Directory |
| quota | Display disk usage and limits |
| quotacheck | Scan a file system for disk usage |
| quotactl | Set disk quotas |
| ram | ram disk device |
| rcp | Copy files between two machines |
| read | Read a line from standard input |
| readarray | Read from stdin into an array variable |
| readonly | Mark variables/functions as readonly |
| reboot | Reboot the system |
| rename | Rename files |
| renice | Alter priority of running processes |
| remsync | Synchronize remote files via email |
| return | Exit a shell function |
| rev | Reverse lines of a file |
| rm | Remove files |
| rmdir | Remove folder(s) |
| rsync | Remote file copy (Synchronize file trees) |
| screen | Multiplex terminal, run remote shells via ssh |
| scp | Secure copy (remote file copy) |
| sdiff | Merge two files interactively |
| sed | Stream Editor |
| select | Accept keyboard input |
| seq | Print numeric sequences |
| set | Manipulate shell variables and functions |
| sftp | Secure File Transfer Program |
| shift | Shift positional parameters |
| shopt | Shell Options |
| shutdown | Shutdown or restart linux |
| sleep | Delay for a specified time |
| slocate | Find files |
| sort | Sort text files |
| source | Run commands from a file `.' |
| split | Split a file into fixed-size pieces |
| ssh | Secure Shell client (remote login program) |
| strace | Trace system calls and signals |
| su | Substitute user identity |
| sudo | Execute a command as another user |
| sum | Print a checksum for a file |
| suspend | Suspend execution of this shell |
| symlink | Make a new name for a file |
| sync | Synchronize data on disk with memory |
| tail | Output the last part of files |
| tar | Tape ARchiver |
| tee | Redirect output to multiple files |
| test | Evaluate a conditional expression |
| time | Measure Program running time |
| times | User and system times |
| touch | Change file timestamps |
| top | List processes running on the system |
| traceroute | Trace Route to Host |
| trap | Run a command when a signal is set(bourne) |
| tr | Translate, squeeze, and/or delete characters |
| TRUE | Do nothing, successfully |
| tsort | Topological sort |
| tty | Print filename of terminal on stdin |
| type | Describe a command |
| ulimit | Limit user resources |
| umask | Users file creation mask |
| umount | Unmount a device |
| unalias | Remove an alias |
| uname | Print system information |
| unexpand | Convert spaces to tabs |
| uniq | Uniquify files |
| units | Convert units from one scale to another |
| unset | Remove variable or function names |
| unshar | Unpack shell archive scripts |
| until | Execute commands (until error) |
| useradd | Create new user account |
| usermod | Modify user account |
| users | List users currently logged in |
| uuencode | Encode a binary file |
| uudecode | Decode a file created by uuencode |
| v | Verbosely list directory contents (`ls -l -b') |
| vdir | Verbosely list directory contents (`ls -l -b') |
| vi | Text Editor |
| vmstat | Report virtual memory statistics |
| watch | Execute/display a program periodically |
| wc | Print byte, word, and line counts |
| whereis | Search the user's $path, man pages and source files for a program |
| which | Search the user's $path for a program file |
| while | Execute commands |
| who | Print all usernames currently logged in |
| whoami | Print the current user id and name (`id -un') |
| Wget | Retrieve web pages or files via HTTP, HTTPS or FTP |
| write | Send a message to another user |
| xargs | Execute utility, passing constructed argument list(s) |
| xdg-open | Open a file or URL in the user's preferred application. |
| yes | Print a string until interrupted |
| . | Run a command script in the current shell |
| !! | Run the last command again |
| ### | Comment / Remark |
