[](https://gitter.im/jlevy/the-art-of-command-line?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
- [Kurzbeschreibung](#meta)
- [Grundlagen](#basics)
- [Täglicher Gebrauch](#everyday-use)
- [Umgang mit Dateien und Daten](#processing-files-and-data)
- [Fehlerbehebung auf Systemebene](#system-debugging)
- [Einzeiler](#one-liners)
- [Eigenartig aber hilfreich](#obscure-but-useful)
Der flüssige Umgang mit der Kommandozeile ist eine oft vernachlässigte oder als undurchsichtig empfundene Fähigkeit, steigert jedoch Flexibilität und Produktivität eines Informatikers auf offensichtliche als auch subtile Weise. Was folgt, ist eine Auswahl an Notizen und Tipps im Umgang mit der Kommandozeile, welche ich beim Arbeiten mit Linux zu schätzen gelernt habe. Manche dieser Hinweise beinhalten Grundwissen, andere sind sehr spezifisch, fortgeschritten oder auch eigenartig. Die Seite ist nicht lang, aber wenn du alle Punkte verstanden hast und anwenden kannst, weißt du eine ganze Menge.
auf [Quora](http://www.quora.com/What-are-some-time-saving-tips-that-every-Linux-user-should-know),
aber angesichts des Interesses scheint es vielversprechend, Github zu nutzen, wo talentiertere Menschen als ich es bin kontinuierlich Verbesserungen vorschlagen können. Wenn du einen Fehler entdeckst oder etwas, das man besser machen könnte, erstelle ein Issue oder einen PR! (Lies aber bitte zuerst die Kurzbeschreibung und überprüfe bereits vorhandene Issues/PRs.)
- Diese Anleitung richtet sich an Anfänger und Fortgeschrittene. Die Ziele sind The goals are *Breite* (alles ist wichtig), *Genauigkeit* (konkrete Beispiele für die gebräuchlichsten Anwendungsfälle) und *Knappheit* (Dinge, die nicht wesentlich sind oder leicht anderswo nachgeschlagen werden können, sollen vermieden werden). Jeder Tipp ist in einer bestimmten Situation wesentlich oder deutlich zeitsparend gegenüber bestehenden Alternativen.
- Sie ist für Linux geschrieben, mit der Ausnahme des Abschnitts "[Nur MacOS X](#macos-x-only)". Viele der anderen Punkte lassen sich nutzen oder sind installierbar auf anderen Unices oder MacOS (oder sogar Cygwin).
- Der Fokus liegt auf interaktiver Bash, allerdings gelten viele Tipps auch auf anderen Shells sowie für allgemeines Bash-Skripting.
- Sie beinhaltet sowohl "normale" Unix-Befehle als auch solche, die bestimmte installierte Pakete voaussetzen -- sofern sie wichtig genug sind, dass sie die Aufnahme in diese Anleitung verdienen.
- Um eine Seite nicht zu sprengen, ist ihr Inhalt durchgängig anhand von Verweisen aufgelistet. Du bist schlau genug, anderswo zusätzliche Informationen nachzuschlagen, sobald du die Idee bzw. den Befehl dahinter kennst. Verwende `apt-get`/`yum`/`dnf`/`pacman`/`pip`/`brew` (je nachdem), um neue Programme zu installieren.
- Verwende [Explainshell](http://explainshell.com/), um einen hilfreichen Einblick zu erhalten, was es mit Befehlen, Optionen, Pipes etc. auf sich hat.
- Lerne einfache Bash. Tatsächlich, gib `man bash` ein und überfliege das Ganze zumindest; es ist leicht zu verstehen und nicht allzu lang. Alternative Shells sind nett, aber Bash ist mächtig und immer verfügbar (*nur* zsh, fish, etc. zu lernen ist auf dem eigenen Laptop vielleicht reizvoll, beschränkt jedoch deine Möglichkeiten in vielerlei Hinsicht, etwa beim Arbeiten mit bestehenden Servern).
- Lerne mindestens einen Text-basierten Editor zu benutzen. Idealerweise Vim (`vi`), da es letztlich keinen vergleichbaren Mitbewerber für gelegentliche Einsätze in einem Terminal gibt (selbst dann, wenn man eine große Entwicklungsumgebung wie Emacs oder die meiste Zeit einen modernen Hipster-Editor benutzt).
- Wisse, wie man Dokumentationen mit `man` liest (für Neugierige, `man man` listet Abschnittsnummern, bspw. stehen unter 1 "reguläre" Befehle, 5 beinhaltet Dateien/Konventionen und unter 8 solche zur Rechnerverwaltung). Finde man-Seiten mit `apropos`. Wisse, dass manche Befehle keine ausführbaren Dateien, sondern Bash-Builtins sind, und dass du Hilfe zu diesen mit `help` und `help -d` erhälst.
- Lerne etwas über die Umleitung von Ein- und Ausgaben per `>` und `<` sowie `|` für Pipes. Wisse, dass `>` die Ausgabedatei überschreibt und `>>` etwas anhängt. Lerne etwas über stdout und stderr.
- Lerne etwas über die Dateinamenerweiterung mittels `*` (und eventuell `?` und `{`...`}`) sowie Anführungszeichen, etwa den Unterschied zwischen doppelten `"` und einfachen `'`. (Mehr zur Variablenerweiterung findest du unten.)
- Grundlegende Dateiverwaltung: `ls` and `ls -l` (und spezieller, lerne die Funktion jeder einzelnen Spalte von `ls -l` kennen), `less`, `head`, `tail` und `tail -f` (oder noch besser, `less +F`), `ln` und `ln -s` (lerne die Unterschiede und Vorteile von Hard- und Softlinks), `chown`, `chmod`, `du` (für eine Kurzzusammenfassung der Festplattenbelegung: `du -hs *`). Für Dateisystemmanagement, `df`, `mount`, `fdisk`, `mkfs`, `lsblk`.
- Kenne reguläre Ausdrücke gut, und die verschiedenen Statusindikatoren zu `grep`/`egrep`. Die Optionen `-i`, `-o`, `-v`, `-A`, `-B`, und `-C` sind gut zu wissen.
- Lerne den Umgang mit `apt-get`, `yum`, `dnf` oder `pacman` (je nach Distribution), um Pakete zu finden bzw. zu installieren. Und stell sicher, dass du `pip` hast, um Python-basierte Kommandozeilen-Tools nutzen zu können (einige der untenstehenden werden am einfachsten über `pip` installiert).
- In Bash kannst du mit **ctrl-w** das letzte Wort löschen und mit **ctrl-u** alles bis zum Anfang einer Zeile. Verwende **alt-b** und **alt-f**, um dich Wort für Wort fortzubewegen, springe mit **ctrl-a** zum Beginn einer Zeile, mit **ctrl-e** zum Ende einer Zeile, lösche mit **ctrl-k** alles bis zum Ende einer Zeile und bereinige mit **ctrl-l** den Bildschirm. Siehe `man readline` für alle voreingestellten Tastenbelegungen in Bash. Davon gibt's viele. Zum Beispiel **alt-.** wechselt durch vorherige Parameter und **alt-*** erweitert ein Suchmuster.
- Um kürzich genutzte Befehle zu sehen, `history`. Es gibt außerdem viele Abkürzungen wie etwa `!$` (letzter Parameter) und `!!` (letzter Befehl), wenngleich diese oft einfach ersetzt werden durch **ctrl-r** und **alt-.**.
- If you are halfway through typing a command but change your mind, hit **alt-#** to add a `#` at the beginning and enter it as a comment (or use **ctrl-a**, **#**, **enter**). You can then return to it later via command history.
- Verwende `xargs` (oder `parallel`). Es ist sehr mächtig. Beachte, wie du viele Dinge pro Zeile (`-L`) als auch parallel (`-P`) ausführen kannst. Wenn du dir nicht sicher bist, ob das Richtige dabei herauskommt, verwende zunächst `xargs echo`. Außerdem ist`-I{}` nützlich. Beispiele:
- Kenne die verschiedenen Signale, die du Prozessen senden kannst. Um einen Prozess etwa zu unterbrechen, verwende `kill -STOP [pid]`. Für die vollständige Liste, siehe `man 7 signal`
- Verwende in Bash-Skripts `set -x` zur Fehlerbehebung. Benutze strict modes wann immer möglich. Verwende `set -e` zum Abbruch bei Fehlern. Benutze `set -o pipefail` ebenfalls, um mit Fehlern präzise zu arbeiten (auch wenn dieses Thema etwas heikel ist). Verwende für etwas komplexere Skripte weiterhin `trap`.
- In Bash-Skripts stellen Subshells (geschrieben in runden Klammern) einen praktischen Weg dar, Befehle zusammenzufassen. Ein gebräuchliches Beispiel ist die vorübergehende Arbeit in einem anderen Arbeitsverzeichnis:
- In Bash, note there are lots of kinds of variable expansion. Checking a variable exists: `${name:?error message}`. For example, if a Bash script requires a single argument, just write `input_file=${1:?usage: $0 input_file}`. Arithmetic expansion: `i=$(( (i + 1) % 5 ))`. Sequences: `{1..10}`. Trimming of strings: `${var%suffix}` and `${var#prefix}`. For example if `var=foo.pdf`, then `echo ${var%.pdf}.txt` prints `foo.txt`.
- The output of a command can be treated like a file via `<(some command)`. For example, compare local `/etc/hosts` with a remote one:
```sh
diff /etc/hosts <(ssh somehost cat /etc/hosts)
```
- Know about "here documents" in Bash, as in `cat <<EOF ...`.
- In Bash, redirect both standard output and standard error via: `some-command >logfile 2>&1`. Often, to ensure a command does not leave an open file handle to standard input, tying it to the terminal you are in, it is also good practice to add `</dev/null`.
- Use `man ascii` for a good ASCII table, with hex and decimal values. For general encoding info, `man unicode`, `man utf-8`, and `man latin1` are helpful.
- Use `screen` or [`tmux`](https://tmux.github.io/) to multiplex the screen, especially useful on remote ssh sessions and to detach and re-attach to a session. A more minimal alternative for session persistence only is `dtach`.
- In ssh, knowing how to port tunnel with `-L` or `-D` (and occasionally `-R`) is useful, e.g. to access web sites from a remote server.
- It can be useful to make a few optimizations to your ssh configuration; for example, this `~/.ssh/config` contains settings to avoid dropped connections in certain network environments, uses compression (which is helpful with scp over low-bandwidth connections), and multiplex channels to the same server with a local control file:
```
TCPKeepAlive=yes
ServerAliveInterval=15
ServerAliveCountMax=6
Compression=yes
ControlMaster auto
ControlPath /tmp/%r@%h:%p
ControlPersist yes
```
- A few other options relevant to ssh are security sensitive and should be enabled with care, e.g. per subnet or host or in trusted networks: `StrictHostKeyChecking=no`, `ForwardAgent=yes`
- To get the permissions on a file in octal form, which is useful for system configuration but not available in `ls` and easy to bungle, use something like
```sh
stat -c '%A %a %n' /etc/timezone
```
- For interactive selection of values from the output of another command, use [`percol`](https://github.com/mooz/percol) or [`fzf`](https://github.com/junegunn/fzf).
- For interaction with files based on the output of another command (like `git`), use `fpp` ([PathPicker](https://github.com/facebook/PathPicker)).
- For a simple web server for all files in the current directory (and subdirs), available to anyone on your network, use:
`python -m SimpleHTTPServer 7777` (for port 7777 and Python 2) and `python -m http.server 7777` (for port 7777 and Python 3).
- For running a command with privileges, use `sudo` (for root) or `sudo -u` (for another user). Use `su` or `sudo bash` to actually run a shell as that user. Use `su -` to simulate a fresh login as root or another user.
## Processing files and data
- To locate a file by name in the current directory, `find . -iname '*something*'` (or similar). To find a file anywhere by name, use `locate something` (but bear in mind `updatedb` may not have indexed recently created files).
- For general searching through source or data files (more advanced than `grep -r`), use [`ag`](https://github.com/ggreer/the_silver_searcher).
- To convert HTML to text: `lynx -dump -stdin`
- For Markdown, HTML, and all kinds of document conversion, try [`pandoc`](http://pandoc.org/).
- If you must handle XML, `xmlstarlet` is old but good.
- For JSON, use [`jq`](http://stedolan.github.io/jq/).
- For Excel or CSV files, [csvkit](https://github.com/onyxfish/csvkit) provides `in2csv`, `csvcut`, `csvjoin`, `csvgrep`, etc.
- For Amazon S3, [`s3cmd`](https://github.com/s3tools/s3cmd) is convenient and [`s4cmd`](https://github.com/bloomreach/s4cmd) is faster. Amazon's [`aws`](https://github.com/aws/aws-cli) is essential for other AWS-related tasks.
- Know about `sort` and `uniq`, including uniq's `-u` and `-d` options -- see one-liners below. See also `comm`.
- Know about `cut`, `paste`, and `join` to manipulate text files. Many people use `cut` but forget about `join`.
- Know about `wc` to count newlines (`-l`), characters (`-m`), words (`-w`) and bytes (`-c`).
- Know about `tee` to copy from stdin to a file and also to stdout, as in `ls -al | tee file.txt`.
- Know that locale affects a lot of command line tools in subtle ways, including sorting order (collation) and performance. Most Linux installations will set `LANG` or other locale variables to a local setting like US English. But be aware sorting will change if you change locale. And know i18n routines can make sort or other commands run *many times* slower. In some situations (such as the set operations or uniqueness operations below) you can safely ignore slow i18n routines entirely and use traditional byte-based sort order, using `export LC_ALL=C`.
- Know basic `awk` and `sed` for simple data munging. For example, summing all numbers in the third column of a text file: `awk '{ x += $3 } END { print x }'`. This is probably 3X faster and 3X shorter than equivalent Python.
- To replace all occurrences of a string in place, in one or more files:
- To rename many files at once according to a pattern, use `rename`. For complex renames, [`repren`](https://github.com/jlevy/repren) may help.
```sh
# Recover backup files foo.bak -> foo:
rename 's/\.bak$//' *.bak
# Full rename of filenames, directories, and contents foo -> bar:
repren --full --preserve-case --from foo --to bar .
```
- Use `shuf` to shuffle or select random lines from a file.
- Know `sort`'s options. For numbers, use `-n`, or `-h` for handling human-readable numbers (e.g. from `du -h`). Know how keys work (`-t` and `-k`). In particular, watch out that you need to write `-k1,1` to sort by only the first field; `-k1` means sort according to the whole line. Stable sort (`sort -s`) can be useful. For example, to sort first by field 2, then secondarily by field 1, you can use `sort -k1,1 | sort -s -k2,2`.
- If you ever need to write a tab literal in a command line in Bash (e.g. for the -t argument to sort), press **ctrl-v****[Tab]** or write `$'\t'` (the latter is better as you can copy/paste it).
- The standard tools for patching source code are `diff` and `patch`. See also `diffstat` for summary statistics of a diff. Note `diff -r` works for entire directories. Use `diff -r tree1 tree2 | diffstat` for a summary of changes.
- For binary files, use `hd` for simple hex dumps and `bvi` for binary editing.
- Also for binary files, `strings` (plus `grep`, etc.) lets you find bits of text.
- For binary diffs (delta compression), use `xdelta3`.
- To convert text encodings, try `iconv`. Or `uconv` for more advanced use; it supports some advanced Unicode things. For example, this command lowercases and removes all accents (by expanding and dropping them):
- To split files into pieces, see `split` (to split by size) and `csplit` (to split by a pattern).
- Use `zless`, `zmore`, `zcat`, and `zgrep` to operate on compressed files.
## System debugging
- For web debugging, `curl` and `curl -I` are handy, or their `wget` equivalents, or the more modern [`httpie`](https://github.com/jakubroztocil/httpie).
- To know disk/cpu/network status, use `iostat`, `netstat`, `top` (or the better `htop`), and (especially) `dstat`. Good for getting a quick idea of what's happening on a system.
- For a more in-depth system overview, use [`glances`](https://github.com/nicolargo/glances). It presents you with several system level statistics in one terminal window. Very helpful for quickly checking on various subsystems.
- To know memory status, run and understand the output of `free` and `vmstat`. In particular, be aware the "cached" value is memory held by the Linux kernel as file cache, so effectively counts toward the "free" value.
- Java system debugging is a different kettle of fish, but a simple trick on Oracle's and some other JVMs is that you can run `kill -3 <pid>` and a full stack trace and heap summary (including generational garbage collection details, which can be highly informative) will be dumped to stderr/logs. The JDK's `jps`, `jstat`, `jstack`, `jmap` are useful. [SJK tools](https://github.com/aragozin/jvm-tools) are more advanced.
- Use `mtr` as a better traceroute, to identify network issues.
- For looking at why a disk is full, `ncdu` saves time over the usual commands like `du -sh *`.
- To find which socket or process is using bandwidth, try `iftop` or `nethogs`.
- The `ab` tool (comes with Apache) is helpful for quick-and-dirty checking of web server performance. For more complex load testing, try `siege`.
- For more serious network debugging, `wireshark`, `tshark`, or `ngrep`.
- Know about `strace` and `ltrace`. These can be helpful if a program is failing, hanging, or crashing, and you don't know why, or if you want to get a general idea of performance. Note the profiling option (`-c`), and the ability to attach to a running process (`-p`).
- Know about `ldd` to check shared libraries etc.
- Know how to connect to a running process with `gdb` and get its stack traces.
- Use `/proc`. It's amazingly helpful sometimes when debugging live problems. Examples: `/proc/cpuinfo`, `/proc/meminfo`, `/proc/cmdline`, `/proc/xxx/cwd`, `/proc/xxx/exe`, `/proc/xxx/fd/`, `/proc/xxx/smaps` (where `xxx` is the process id or pid).
- When debugging why something went wrong in the past, `sar` can be very helpful. It shows historic statistics on CPU, memory, network, etc.
- For deeper systems and performance analyses, look at `stap` ([SystemTap](https://sourceware.org/systemtap/wiki)), [`perf`](http://en.wikipedia.org/wiki/Perf_(Linux)), and [`sysdig`](https://github.com/draios/sysdig).
- Check what OS you're on with `uname` or `uname -a` (general Unix/kernel info) or `lsb_release -a` (Linux distro info).
- Use `dmesg` whenever something's acting really funny (it could be hardware or driver issues).
## One-liners
A few examples of piecing together commands:
- It is remarkably helpful sometimes that you can do set intersection, union, and difference of text files via `sort`/`uniq`. Suppose `a` and `b` are text files that are already uniqued. This is fast, and works on files of arbitrary size, up to many gigabytes. (Sort is not limited by memory, though you may need to use the `-T` option if `/tmp` is on a small root partition.) See also the note about `LC_ALL` above and `sort`'s `-u` option (left out for clarity below).
```sh
cat a b | sort | uniq > c # c is a union b
cat a b | sort | uniq -d > c # c is a intersect b
cat a b b | sort | uniq -u > c # c is set difference a - b
```
- Use `grep . *` to visually examine all contents of all files in a directory, e.g. for directories filled with config settings, like `/sys`, `/proc`, `/etc`.
- Summing all numbers in the third column of a text file (this is probably 3X faster and 3X less code than equivalent Python):
```sh
awk '{ x += $3 } END { print x }' myfile
```
- If want to see sizes/dates on a tree of files, this is like a recursive `ls -l` but is easier to read than `ls -lR`:
```sh
find . -type f -ls
```
- Say you have a text file, like a web server log, and a certain value that appears on some lines, such as an `acct_id` parameter that is present in the URL. If you want a tally of how many requests for each `acct_id`:
- To continuously monitor changes, use `watch`, e.g. check changes to files in a directory with `watch -d -n 2 'ls -rtlh | tail'` or to network settings while troubleshooting your wifi settings with `watch -d -n 2 ifconfig`.
- Run this function to get a random tip from this document (parses Markdown and extracts an item):
-`tree`: display directories and subdirectories as a nesting tree; like `ls` but recursive
-`stat`: file info
-`time`: execute and time a command
-`watch`: run a command repeatedly, showing results and/or highlighting changes
-`tac`: print files in reverse
-`shuf`: random selection of lines from a file
-`comm`: compare sorted files line by line
-`pv`: monitor the progress of data through a pipe
-`hd` and `bvi`: dump or edit binary files
-`strings`: extract text from binary files
-`tr`: character translation or manipulation
-`iconv` or `uconv`: conversion for text encodings
-`split` and `csplit`: splitting files
-`sponge`: read all input before writing it, useful for reading from then writing to the same file, e.g., `grep -v something some-file | sponge some-file`
-`units`: unit conversions and calculations; converts furlongs per fortnight to twips per blink (see also `/usr/share/units/definitions.units`)
-`7z`: high-ratio file compression
-`ldd`: dynamic library info
-`nm`: symbols from object files
-`ab`: benchmarking web servers
-`strace`: system call debugging
-`mtr`: better traceroute for network debugging
-`cssh`: visual concurrent shell
-`rsync`: sync files and folders over SSH or in local file system
-`wireshark` and `tshark`: packet capture and network debugging
-`ngrep`: grep for the network layer
-`host` and `dig`: DNS lookups
-`lsof`: process file descriptor and socket info
-`dstat`: useful system stats
- [`glances`](https://github.com/nicolargo/glances): high level, multi-subsystem overview
-`iostat`: Disk usage stats
-`mpstat`: CPU usage stats
-`vmstat`: Memory usage stats
-`htop`: improved version of top
-`last`: login history
-`w`: who's logged on
-`id`: user/group identity info
-`sar`: historic system stats
-`iftop` or `nethogs`: network utilization by socket or process
-`ss`: socket statistics
-`dmesg`: boot and system error messages
-`sysctl`: view and configure Linux kernel parameters at run time
-`hdparm`: SATA/ATA disk manipulation/performance
-`lsb_release`: Linux distribution info
-`lsblk`: list block devices: a tree view of your disks and disk paritions
-`lshw`, `lscpu`, `lspci`, `lsusb`, `dmidecode`: hardware information, including CPU, BIOS, RAID, graphics, devices, etc.
-`lsmod` and `modifno`: List and show details of kernel modules.
-`fortune`, `ddate`, and `sl`: um, well, it depends on whether you consider steam locomotives and Zippy quotations "useful"
## MacOS X only
These are items relevant *only* on MacOS.
- Package management with `brew` (Homebrew) and/or `port` (MacPorts). These can be used to install on MacOS many of the above commands.
- Copy output of any command to a desktop app with `pbcopy` and paste input from one with `pbpaste`.
- To enable the Option key in Mac OS Terminal as an alt key (such as used in the commands above like **alt-b**, **alt-f**, etc.), open Preferences -> Profiles -> Keyboard and select "Use Option as Meta key".
- To open a file with a desktop app, use `open` or `open -a /Applications/Whatever.app`.
- Spotlight: Search files with `mdfind` and list metadata (such as photo EXIF info) with `mdls`.
- Be aware MacOS is based on BSD Unix, and many commands (for example `ps`, `ls`, `tail`, `awk`, `sed`) have many subtle variations from Linux, which is largely influenced by System V-style Unix and GNU tools. You can often tell the difference by noting a man page has the heading "BSD General Commands Manual." In some cases GNU versions can be installed, too (such as `gawk` and `gsed` for GNU awk and sed). If writing cross-platform Bash scripts, avoid such commands (for example, consider Python or `perl`) or test carefully.
## More resources
- [awesome-shell](https://github.com/alebcay/awesome-shell): A curated list of shell tools and resources.
- [Strict mode](http://redsymbol.net/articles/unofficial-bash-strict-mode/) for writing better shell scripts.
- [shellcheck](https://github.com/koalaman/shellcheck) - A shell script static analysis tool. Essentially, lint for bash/sh/zsh.
## Disclaimer
With the exception of very small tasks, code is written so others can read it. With power comes responsibility. The fact you *can* do something in Bash doesn't necessarily mean you should! ;)
