This page should serve as a reference for the many "things Linux" we use in this course. It is by no means complete – Linux is **huge** – but offers introductions to many important topics.
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Some Linux commands
- This page provides lists of the most common Linux commands, by category, as well as their most useful options:
Terminal programs, shells and commands
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- Macs and Linux have a Terminal program built-in
- Windows options:
- Windows 10+
- Command Prompt and PowerShell programs have ssh and scp (may require latest Windows updates)
- Start menu → Search for Command
- Putty – http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html
- simple Terminal and file copy programs
- download either the Putty installer or just putty.exe (Terminal) and pscp.exe (secure copy client)
- Windows Subsystem for Linux – Windows 10 Professional includes a Ubuntu-like bash shells
- See https://docs.microsoft.com/en-us/windows/wsl/install-win10
- We recommend the Ubuntu Linux distribution, but any Linux distribution will have an SSH client
- Command Prompt and PowerShell programs have ssh and scp (may require latest Windows updates)
- Windows 10+
Use ssh (secure shell) to login to a remote computers.
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# General form: ssh <user_name>@<full_host_name> # For example ssh abattenh@ls6.tacc.utexas.edu |
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# You type the name of a command that is not installed on your system ls6:~$ lz Command 'lz' not found, but can be installed with: apt install mtools Please ask your administrator. # You enter something that is close to an existing, or known, command ls6:~$ catt Command 'catt' not found, did you mean: command 'cat' from deb coreutils (8.30-3ubuntu2) command 'catty' from deb node-catty (0.0.8-1) command 'ratt' from deb ratt (0.0~git20180127.c44413c-2) Try: apt install <deb name> # You try to use an unsupported option ls6:~$ ls -z ls: invalid option -- 'z' Try 'ls --help' for more information. # You specify the name of a file that does not exist ls6:~$ ls xxx ls: cannot access 'xxx': No such file or directory |
Basic Linux commands
One of the steepest Unix/Linux learning curves is the sheer number of built-in commands, all of which have many options – most of which you'll never use, and the more advanced commands are extremely complex.
To help address this, this section introduces a number of built-in Linux utilities along with some of their common options, by category.
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Most built-in Linux commands that obtain data from a file can also accept the data piped in on their standard input. |
And here's a Linux commands cheat sheet you may find useful: 
Displaying file contents
- cat outputs all the contents of its input (one or more files and/or standard input) or the specified file
- cat -n prefixes each line of output with its line number
- CAUTION – only use on small files!
- zcat <file.gz> like cat, but understands the gzip (.gz) format, and decompresses the data before writing it to standard output
- CAUTION – only use on small files!
- Another CAUTION – does not understand .zip or .bz2 compression formats
- more and less pagers
- both display their (possibly very long) input one Terminal "page" at a time
- in more:
- use spacebar to advance a page
- use q or Ctrl-c to exit more
- in less:
- q – quit
- Ctrl-f or space – page forward
- Ctrl-b – page backward
- /<pattern> – search for <pattern> in forward direction
- n – next match
- N – previous match
- ?<pattern> – search for <pattern> in backward direction
- n – previous match going back
- N – next match going forward
- use less -N to display line numbers
- less -I says to do pattern matching ignoring case
- can be used directly on .gz format files
- head and tail
- show you the first or last 10 lines (by default) of their input
- head -n 20 or just head -20 shows the first 20 lines
- tail -n 2 or just tail -2 shows the last 2 lines
- tail -n +100 shows lines starting at line 100
- tail -n +100 | head -20 shows 20 lines starting at line 100
- tail -f shows the last lines of a file, then follows the output as more lines are written (Ctrl-c to quit)
- gunzip -c <file.gz> | more (or less) – like zcat, un-compresses lines of <file.gz> and outputs them to standard output
- <file.gz> is not altered on disk
- always pipe the output to a pager!
File system navigation
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- -l says produce a long listing (including file permissions, sizes, owner and group)
- -a says show all files, even normally-hidden dot files whose names start with a period ( . )
- -h says to show file sizes in human readable form (e.g. 12M instead of 12201749)
- -t says to sort files on last modification time
- -r says to reverse the current sort order
- -d says to show directory listing information only, instead of directory contents
- usually combined with -l, e.g.: ls -ld <dirname>
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- .. (period, period) means "up one directory level"
- ~ (tilde) means "my Home directory"
- - (dash) means "the last directory I was in"
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- -h says to show sizes in human readable form (e.g. 12G instead of 12318201749)
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- -P says to display the full absolute path, resolving any symbolic links or relative path syntax
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- tree is not always available on all Linux systems
Create, rename, link to, delete files
- touch <file> – create an empty file, or update the modification timestamp on an existing file
- mkdir -p <dirname> – create directory <dirname>.
- -p says to create any needed sub-directories also
- mv <file1> <file2> – renames <file1> to <file2>
- mv <file1> <file2> ... <fileN> <to_dir>/ – moves files <file1> <file2> ... <fileN> into directory <to_dir>
- mv -t <dir> <file1> <file2> ... <fileN> – same as above, but specifies the target directory as an option (-t <to_dir>)
- ln -s <path> creates a symbolic (-s) link (a.k.a symlink) to <path> in the current directory
- default link name corresponds to the last name component in <path>
- always change into (cd) the directory where you want the link before executing ln -s
- a symbolic link can be deleted without affecting the linked-to file
- ln -sf -t <target_dir> <file1> <file2> ... <fileN> – creates symbolic links to <file1> <file2> ... <fileN> in target directory <target_dir>
- rm <file> deletes a file. This is permanent - not a "trash can" deletion.
- rm -rf <dirname> deletes an entire directory – be careful!
Copying files and directories
- cp <source> [<source>...] <destination> copies the file(s) <source> [<source>...] to the directory and/or file name <destination>.
- using . (period) as the destination means "here, with the same name"
- -p option says to preserve file modification timestamps
- cp -r <dirname>/ <destination>/ will recursively copy the directory <dirname>/ and all its contents to the directory <destination>/.
- scp <user>@<host>:<remote_source_path> <local_destination_path>
- Works just like cp but copies <remote_source_path> from the remote host machine to the <local_destination_path>
- -p (preserve file times) and -r (recursive) options work the same as cp
- scp <local_source_path> <user>@<host>:<remote_destination_path> is similar, but copies the <local_source_path> to the <remote_destination_path> on the remote host machine.
- A nice scp syntax resource is located here.
- wget <url> fetches a file from a valid URL (e.g. http, https, ftp).
- -O <file> specifies the name for the local file (defaults to the last component of the URL)
- rsync -arvW <source_directory>/ <target_directory>/
rsync -ptlrvP <source_directory>/ <target_directory>/- Recursively copies <source_directory> contents to <target_directory>, but only if <source_directory> files are newer or don't yet exist in <target_directory>
Remote path syntax (<user>@<host>:<absolute_or_home-relative_path>) can be used for either source or target (but not both).
- Always include a trailing slash ( / ) after the source and target directory names!
- -a means "archive" mode (equivalent to -ptl and some other options)
- -r means recursively copy sub-directories
- -v means verbose
- -W means Whole file only
- Normally the rsync algorithm compares the contents of files that need to be copied and only transfers the different portions. This option disables file content comparisons, which are not appropriate for large and/or binary files.
- -p means preserve file permissions
- -t means preserve file times
- -l means copy symbolic links as links (vs -L which means dereference the link and copy the file it refers to)
- -P means show transfer Progress (useful when large files are being transferred)
Miscellaneous commands
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- evaluation of metacharacters (special characters) inside the text may be performed first
- -e says to enable conversion of backslash escapes such as \t Tab and \n newline to their ASCII character
- -n says not to output the trailing newline
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- wc -c reports the number of characters (-c) in its input
- wc -w reports the number of words (-w) in its input
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- redirect to a file to save a history of the commands executed in a shell session
- pipe to grep to search for a particular command
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- shows the disk usage (size) of the specified files/directories
- -h says report the size in human-readable form (e.g. 12M instead of 12201749)
- -s says summarize the directory size for directories
- -c says print a grand total when multiple items are specified
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Advanced commands
cut, sort, uniq
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Navigation and operations in nano are similar to those we discussed in Command line editing
You can just type in text, and navigate around using arrow keys (up/down/left/right). A couple of other navigation shortcuts:
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