Linux command line cheat sheet

1. 1Filesystem and navigationLinux has one directory tree starting at /, with a conventional place for everything. Knowing the layout tells you where to look.7 concepts

   1. 1Filesystem layoutEverything hangs off /.
   2. 2Absolute and relative pathsAn absolute path starts at /, such as /var/log/syslog.
   3. 3Moving around and listingpwd prints where you are, cd changes directory (cd - goes back, cd alone goes home), and ls lists contents with options for details, hidden files and…
   4. 4Creating, copying, moving and deletingmkdir -p creates directories including parents, touch creates an empty file, cp -r copies, mv moves or renames, and rm deletes (-r for directories).
   5. 5Globs and hidden filesThe shell expands globs before running a command: * matches any characters, ? one character, [abc] a set, and {a,b} expands to both words.
   6. 6Hard and symbolic linksA symbolic link is a small file pointing to a path.
   7. 7Getting helpman cmd opens the manual page, cmd --help prints a short usage summary, and type cmd tells you whether a name is a program, a shell builtin or an alias.

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2. 2Files and text toolsLinux tools treat text as lines. Small programs that each do one thing well can be chained to answer most questions about logs and data.8 concepts

   1. 1Viewing filescat prints a file, less pages through it (search with /, quit with q), head and tail show the first or last lines, and tail -f follows a file as…
   2. 2findfind walks a directory tree and matches files by name, type, size, age or owner, then prints them or runs an action on each.
   3. 3grepgrep prints lines matching a pattern.
   4. 4sedsed edits text as it streams past, most often substituting with s/old/new/g.
   5. 5awkawk splits each line into fields ($1, $2, $NF for the last) and runs a small program per line, with patterns, variables and sums.
   6. 6sort, uniq, cut and wcsort orders lines (-n numeric, -r reverse, -k by column), uniq collapses adjacent duplicates (-c counts them), cut extracts fields by delimiter…
   7. 7xargsxargs reads items from standard input and passes them as arguments to a command, in batches.
   8. 8diff and comparing filesdiff -u shows line differences between two files in unified format.

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3. Redirection, pipes and the shellEvery program has three standard streams. Redirecting and joining them is what makes the command line composable.7 conceptsOpens with credits
4. Permissions, users and sudoEvery file has an owner, a group and permission bits, and every process runs as some user. Together they decide who can do what.7 conceptsOpens with credits
5. Processes, jobs and servicesEvery running program is a process. You inspect, signal and schedule them, and systemd keeps long-running services alive.7 conceptsOpens with credits
6. Packages, disks and memoryInstalling software and keeping an eye on disk, memory and load: the checks you run on any server that misbehaves.6 conceptsOpens with credits
7. Networking commands and SSHChecking addresses and ports, fetching URLs, and working securely on remote machines with SSH.7 conceptsOpens with credits
8. Environment, archives and schedulingHow the shell finds programs and settings, how to pack files up, and how to run jobs on a schedule.7 conceptsOpens with credits
9. Bash scriptingWhen you type the same commands twice, put them in a script. These are the pieces of Bash you need to write scripts that are safe to run.9 conceptsOpens with credits
10. 10Glossary, A to ZEvery concept in the sheet and the smaller terms it uses, in one list.97 terms

The Linux shell from first commands to safe Bash scripts: files, text tools, permissions, processes, services, SSH and more.