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Искусство командной строки

Описание
Основы
Ежедневное использование
Процессинг файлов и информации
Системный дебаггинг
Команды в одну строчку
Сложно, но полезно
Только для Маководов
Больше информации по теме
Disclaimer

$curl -s 'https://raw.githubusercontent.com/jlevy/the-art-of-command-line/master/README.md' | egrep -o '\w+' | tr -d '`' | cowsay -W50$

Продвинутому использованию командной строки зачастую не уделяют достаточного внимания, о терминале говорят как о чем-то мистическом; на самом же деле это умение очевидно и не очевидно увеличивает Вашу продуктивность в работе. Данный документ является подборкой заметок и советов, которые я нашел для себя полезными, работая с командной строкой в Linux. Некоторые из их них – простые и очевидные, но некоторые довольно сложные и предназначены для решения конкретных задач. Это небольшая публикация, но если Вы знаете обо всем, что тут написано, и можете вспомнить как это все использовать – вы много знаете!

Многое из того, что тут написано изначально появилось на Quora, начав идею там, похоже, что стоит развить ее на Gihub, где обитают люди, которые талантлевее меня и могут предлагать улучения данной подборки. Если Вы заметили ошибки (во всех вариантах перевода), пожалуйста оставьте тикет или киньте пулл-реквест (заранее изучив описание и посмотрев на уже созданнные тикеты и пулл-реквесты).

Основы

Выучите основы Баша. Просто возьмите и напечатайте man bash в терминале и хотя бы просмотрите его; он довольно просто читается и он не очень большой. Другие шеллы тоже могут быть хороши, но Баш – мощная программа и Баш всегда под рукой (использование исключительно zsh, fish и т.д., которые наверняка круто выглядят на Вашем ноуте во многом Вас ограничивает, например Вы не сможете использовать возможности этих шеллов на уже существующем сервере).
Выучите хотя бы один консольный редактор текста. Идеально Vim (vi), ведь у него нет конкурентов, когда вам нужно быстренько что-то подправить (даже если Вы постоянно сидите на Emacs/какой-нибудь тяжелой IDE или на каком-нибудь модном хипстерском редакторе)
Знайте как читать документацию через man (для любознательных – man man; man по углам документа в скобках добавляет номер, например 1 – для обычных команд, 5 – для файлов, конвенций, 8 – для администативных команд). Ищите мануалы через apropos, и помните, что некоторые команды – не бинарники, а встроенные команды Баша, и помощь по ним можно получить через help и help -d.
Узнайте о том, как перенаправлять ввод и вывод через > и < и пайпы |. Помните, что > – переписывает выходной файл, а >> добавляет к нему. Узнайте побольше про stdout and stderr.
Узнайте побольше про file glob expansion with * (and perhaps ? and {...}), кавычки а так же разницу между двойными " и одинарными ' кавычками. (Больше о расширении переменных читайте ниже)
Будьте знакомы с работой с процессами в Bash: &, ctrl-z, ctrl-c, jobs, fg, bg, kill, и т.д.
Знайте ssh, и основы безпарольной аунтефикации через ssh-agent, ssh-add, и т.д.
Основы работы с файлами: ls и ls -l (в частности узнайте, что значит каждый столбец в ls -l), less, head, tail и tail -f (или даже лучше, less +F), ln и ln -s (узнайте разницу между символьными ссылками и жесткими ссылками и почему жесткие ссылки лучше), chown, chmod, du (для быстрой сводки по использованию диска: du -hk *). Для менеджмента файловой системы, df, mount, fdisk, mkfs, lsblk.
Основы работы с сетью: ip или ifconfig, dig.
Хорошо знайте регулярные выражения и разные флаги к grep/egrep. Такие флаги как -i, -o, -A, и -B стоит знать.
Обучитесь использованию системами управления пакетами apt-get, yum, dnf или pacman (в зависимости от дистрибутива). Занйте как искать и устанавливать пакеты и обязательно имейте установленым pip для установки командных утилит, написаных на Python (некоторые из тех, что вы найдете ниже легче всего установить через pip)

Everyday use

In Bash, use Tab to complete arguments and ctrl-r to search through command history.
In Bash, use ctrl-w to delete the last word, and ctrl-u to delete all the way back to the start of the line. Use alt-b and alt-f to move by word, ctrl-k to kill to the end of the line, ctrl-l to clear the screen. See man readline for all the default keybindings in Bash. There are a lot. For example alt-. cycles through previous arguments, and alt-* expands a glob.
Alternatively, if you love vi-style key-bindings, use set -o vi.
To see recent commands, history. There are also many abbreviations such as !$ (last argument) and !! last command, though these are often easily replaced with ctrl-r and alt-..
To go back to the previous working directory: cd -
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.
Use xargs (or parallel). It's very powerful. Note you can control how many items execute per line (-L) as well as parallelism (-P). If you're not sure if it'll do the right thing, use xargs echo first. Also, -I{} is handy. Examples:

      find . -name '*.py' | xargs grep some_function
      cat hosts | xargs -I{} ssh root@{} hostname

pstree -p is a helpful display of the process tree.
Use pgrep and pkill to find or signal processes by name (-f is helpful).
Know the various signals you can send processes. For example, to suspend a process, use kill -STOP [pid]. For the full list, see man 7 signal
Use nohup or disown if you want a background process to keep running forever.
Check what processes are listening via netstat -lntp or ss -plat (for TCP; add -u for UDP).
See also lsof for open sockets and files.
Use alias to create shortcuts for commonly used commands. For example, alias ll='ls -latr' creates a new alias ll.
In Bash scripts, use set -x for debugging output. Use strict modes whenever possible. Use set -e to abort on errors. Use set -o pipefail as well, to be strict about errors (though this topic is a bit subtle). For more involved scripts, also use trap.
In Bash scripts, subshells (written with parentheses) are convenient ways to group commands. A common example is to temporarily move to a different working directory, e.g.

      # do something in current dir
      (cd /some/other/dir && other-command)
      # continue in original dir

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:

      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 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, use 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

      stat -c '%A %a %n' /etc/timezone

For interactive selection of values from the output of another command, use percol or fzf.
For interaction with files based on the output of another command (like git), use fpp (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.
To convert HTML to text: lynx -dump -stdin
For Markdown, HTML, and all kinds of document conversion, try pandoc.
If you must handle XML, xmlstarlet is old but good.
For JSON, use jq.
For Excel or CSV files, csvkit provides in2csv, csvcut, csvjoin, csvgrep, etc.
For Amazon S3, s3cmd is convenient and s4cmd is faster. Amazon's aws 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:

      perl -pi.bak -e 's/old-string/new-string/g' my-files-*.txt

To rename many files at once according to a pattern, use rename. For complex renames, repren may help.

      # 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):

      uconv -f utf-8 -t utf-8 -x '::Any-Lower; ::Any-NFD; [:Nonspacing Mark:] >; ::Any-NFC; ' < input.txt > output.txt

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.
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. 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.
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/xxx/cwd, /proc/xxx/exe, /proc/xxx/fd/, /proc/xxx/smaps.
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), perf, and 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).

      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):

      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:

      find . -type f -ls

Use xargs or parallel whenever you can. Note you can control how many items execute per line (-L) as well as parallelism (-P). If you're not sure if it'll do the right thing, use xargs echo first. Also, -I{} is handy. Examples:

      find . -name '*.py' | xargs grep some_function
      cat hosts | xargs -I{} ssh root@{} hostname

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:

      cat access.log | egrep -o 'acct_id=[0-9]+' | cut -d= -f2 | sort | uniq -c | sort -rn

Run this function to get a random tip from this document (parses Markdown and extracts an item):

      function taocl() {
        curl -s https://raw.githubusercontent.com/jlevy/the-art-of-command-line/master/README.md |
          pandoc -f markdown -t html |
          xmlstarlet fo --html --dropdtd |
          xmlstarlet sel -t -v "(html/body/ul/li[count(p)>0])[$RANDOM mod last()+1]" |
          xmlstarlet unesc | fmt -80
      }

Obscure but useful

expr: perform arithmetic or boolean operations or evaluate regular expressions
m4: simple macro processor
yes: print a string a lot
cal: nice calendar
env: run a command (useful in scripts)
printenv: print out environment variables (useful in debugging and scripts)
look: find English words (or lines in a file) beginning with a string
cut and paste and join: data manipulation
fmt: format text paragraphs
pr: format text into pages/columns
fold: wrap lines of text
column: format text into columns or tables
expand and unexpand: convert between tabs and spaces
nl: add line numbers
seq: print numbers
bc: calculator
factor: factor integers
gpg: encrypt and sign files
toe: table of terminfo entries
nc: network debugging and data transfer
socat: socket relay and tcp port forwarder (similar to netcat)
slurm: network trafic visualization
dd: moving data between files or devices
file: identify type of a file
tree: display directories and subdirectories as a nesting tree; like ls but recursive
stat: file info
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
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: high level, multi-subsystem overview
iostat: CPU and disk 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
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.
fortune, ddate, and sl: um, well, it depends on whether you consider steam locomotives and Zippy quotations "useful"

MacOS 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 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: A curated list of shell tools and resources.
Strict mode for writing better shell scripts.

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! ;)

License

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

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