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Diffstat (limited to 'bash.html.markdown')
| -rw-r--r-- | bash.html.markdown | 225 |
1 files changed, 172 insertions, 53 deletions
diff --git a/bash.html.markdown b/bash.html.markdown index 271ef62c..11ce4e74 100644 --- a/bash.html.markdown +++ b/bash.html.markdown @@ -11,82 +11,121 @@ contributors: - ["Rahil Momin", "https://github.com/iamrahil"] - ["Gregrory Kielian", "https://github.com/gskielian"] - ["Etan Reisner", "https://github.com/deryni"] - - ["Jonathan Wang", "https://github.com/Jonathansw"] + - ["Jonathan Wang", "https://github.com/Jonathansw"] - ["Leo Rudberg", "https://github.com/LOZORD"] - ["Betsy Lorton", "https://github.com/schbetsy"] - ["John Detter", "https://github.com/jdetter"] + - ["Harry Mumford-Turner", "https://github.com/harrymt"] + - ["Martin Nicholson", "https://github.com/mn113"] filename: LearnBash.sh +translators: + - ["Dimitri Kokkonis", "https://github.com/kokkonisd"] --- -Bash is a name of the unix shell, which was also distributed as the shell for the GNU operating system and as default shell on Linux and Mac OS X. -Nearly all examples below can be a part of a shell script or executed directly in the shell. +Bash is a name of the unix shell, which was also distributed as the shell +for the GNU operating system and as the default shell on most Linux distros. +Nearly all examples below can be a part of a shell script +or executed directly in the shell. -[Read more here.](http://www.gnu.org/software/bash/manual/bashref.html) +[Read more here.](https://www.gnu.org/software/bash/manual/bashref.html) ```bash -#!/bin/bash -# First line of the script is shebang which tells the system how to execute -# the script: http://en.wikipedia.org/wiki/Shebang_(Unix) +#!/usr/bin/env bash +# First line of the script is the shebang which tells the system how to execute +# the script: https://en.wikipedia.org/wiki/Shebang_(Unix) # As you already figured, comments start with #. Shebang is also a comment. # Simple hello world example: -echo Hello world! +echo Hello world! # => Hello world! -# Each command starts on a new line, or after semicolon: +# Each command starts on a new line, or after a semicolon: echo 'This is the first line'; echo 'This is the second line' +# => This is the first line +# => This is the second line # Declaring a variable looks like this: Variable="Some string" # But not like this: -Variable = "Some string" +Variable = "Some string" # => returns error "Variable: command not found" # Bash will decide that Variable is a command it must execute and give an error # because it can't be found. -# Or like this: -Variable= 'Some string' +# Nor like this: +Variable= 'Some string' # => returns error: "Some string: command not found" # Bash will decide that 'Some string' is a command it must execute and give an # error because it can't be found. (In this case the 'Variable=' part is seen # as a variable assignment valid only for the scope of the 'Some string' # command.) # Using the variable: -echo $Variable -echo "$Variable" -echo '$Variable' +echo $Variable # => Some string +echo "$Variable" # => Some string +echo '$Variable' # => $Variable # When you use the variable itself — assign it, export it, or else — you write # its name without $. If you want to use the variable's value, you should use $. # Note that ' (single quote) won't expand the variables! # Parameter expansion ${ }: -echo ${Variable} +echo ${Variable} # => Some string # This is a simple usage of parameter expansion -# Parameter Expansion gets a value from a variable. It "expands" or prints the value -# During the expansion time the value or parameter are able to be modified +# Parameter Expansion gets a value from a variable. +# It "expands" or prints the value +# During the expansion time the value or parameter can be modified # Below are other modifications that add onto this expansion # String substitution in variables -echo ${Variable/Some/A} +echo ${Variable/Some/A} # => A string # This will substitute the first occurrence of "Some" with "A" # Substring from a variable Length=7 -echo ${Variable:0:Length} +echo ${Variable:0:Length} # => Some st # This will return only the first 7 characters of the value +echo ${Variable: -5} # => tring +# This will return the last 5 characters (note the space before -5) + +# String length +echo ${#Variable} # => 11 + +# Indirect expansion +OtherVariable="Variable" +echo ${!OtherVariable} # => Some String +# This will expand the value of OtherVariable # Default value for variable echo ${Foo:-"DefaultValueIfFooIsMissingOrEmpty"} +# => DefaultValueIfFooIsMissingOrEmpty # This works for null (Foo=) and empty string (Foo=""); zero (Foo=0) returns 0. # Note that it only returns default value and doesn't change variable value. +# Declare an array with 6 elements +array0=(one two three four five six) +# Print first element +echo $array0 # => "one" +# Print first element +echo ${array0[0]} # => "one" +# Print all elements +echo ${array0[@]} # => "one two three four five six" +# Print number of elements +echo ${#array0[@]} # => "6" +# Print number of characters in third element +echo ${#array0[2]} # => "5" +# Print 2 elements starting from forth +echo ${array0[@]:3:2} # => "four five" +# Print all elements. Each of them on new line. +for i in "${array0[@]}"; do + echo "$i" +done + # Brace Expansion { } # Used to generate arbitrary strings -echo {1..10} -echo {a..z} +echo {1..10} # => 1 2 3 4 5 6 7 8 9 10 +echo {a..z} # => a b c d e f g h i j k l m n o p q r s t u v w x y z # This will output the range from the start value to the end value -# Builtin variables: -# There are some useful builtin variables, like +# Built-in variables: +# There are some useful built-in variables, like echo "Last program's return value: $?" echo "Script's PID: $$" echo "Number of arguments passed to script: $#" @@ -98,7 +137,7 @@ echo "Script's arguments separated into different variables: $1 $2..." # Our current directory is available through the command `pwd`. # `pwd` stands for "print working directory". -# We can also use the builtin variable `$PWD`. +# We can also use the built-in variable `$PWD`. # Observe that the following are equivalent: echo "I'm in $(pwd)" # execs `pwd` and interpolates output echo "I'm in $PWD" # interpolates the variable @@ -114,13 +153,14 @@ read Name # Note that we didn't need to declare a new variable echo Hello, $Name! # We have the usual if structure: -# use 'man test' for more info about conditionals +# use `man test` for more info about conditionals if [ $Name != $USER ] then echo "Your name isn't your username" else echo "Your name is your username" fi +# True if the value of $Name is not equal to the current user's login username # NOTE: if $Name is empty, bash sees the above condition as: if [ != $USER ] @@ -133,7 +173,11 @@ if [ "" != $USER ] ... # There is also conditional execution echo "Always executed" || echo "Only executed if first command fails" +# => Always executed echo "Always executed" && echo "Only executed if first command does NOT fail" +# => Always executed +# => Only executed if first command does NOT fail + # To use && and || with if statements, you need multiple pairs of square brackets: if [ "$Name" == "Steve" ] && [ "$Age" -eq 15 ] @@ -146,22 +190,39 @@ then echo "This will run if $Name is Daniya OR Zach." fi +# There is also the `=~` operator, which tests a string against a Regex pattern: +Email=me@example.com +if [[ "$Email" =~ [a-z]+@[a-z]{2,}\.(com|net|org) ]] +then + echo "Valid email!" +fi +# Note that =~ only works within double [[ ]] square brackets, +# which are subtly different from single [ ]. +# See https://www.gnu.org/software/bash/manual/bashref.html#Conditional-Constructs for more on this. + +# Redefine command `ping` as alias to send only 5 packets +alias ping='ping -c 5' +# Escape the alias and use command with this name instead +\ping 192.168.1.1 +# Print all aliases +alias -p + # Expressions are denoted with the following format: -echo $(( 10 + 5 )) +echo $(( 10 + 5 )) # => 15 # Unlike other programming languages, bash is a shell so it works in the context # of a current directory. You can list files and directories in the current # directory with the ls command: -ls +ls # Lists the files and subdirectories contained in the current directory -# These commands have options that control their execution: +# This command has options that control its execution: ls -l # Lists every file and directory on a separate line -ls -t # Sort the directory contents by last-modified date (descending) +ls -t # Sorts the directory contents by last-modified date (descending) ls -R # Recursively `ls` this directory and all of its subdirectories # Results of the previous command can be passed to the next command as input. -# grep command filters the input with provided patterns. That's how we can list -# .txt files in the current directory: +# The `grep` command filters the input with provided patterns. +# That's how we can list .txt files in the current directory: ls -l | grep "\.txt" # Use `cat` to print files to stdout: @@ -169,7 +230,12 @@ cat file.txt # We can also read the file using `cat`: Contents=$(cat file.txt) -echo "START OF FILE\n$Contents\nEND OF FILE" +# "\n" prints a new line character +# "-e" to interpret the newline escape characters as escape characters +echo -e "START OF FILE\n$Contents\nEND OF FILE" +# => START OF FILE +# => [contents of file.txt] +# => END OF FILE # Use `cp` to copy files or directories from one place to another. # `cp` creates NEW versions of the sources, @@ -187,13 +253,16 @@ cp -r srcDirectory/ dst/ # recursively copy # `mv` is also useful for renaming files! mv s0urc3.txt dst.txt # sorry, l33t hackers... -# Since bash works in the context of a current directory, you might want to +# Since bash works in the context of a current directory, you might want to # run your command in some other directory. We have cd for changing location: cd ~ # change to home directory +cd # also goes to home directory cd .. # go up one directory # (^^say, from /home/username/Downloads to /home/username) cd /home/username/Documents # change to specified directory cd ~/Documents/.. # still in home directory..isn't it?? +cd - # change to last directory +# => /home/username/Documents # Use subshells to work across directories (echo "First, I'm here: $PWD") && (cd someDir; echo "Then, I'm here: $PWD") @@ -203,6 +272,8 @@ pwd # still in first directory mkdir myNewDir # The `-p` flag causes new intermediate directories to be created as necessary. mkdir -p myNewDir/with/intermediate/directories +# if the intermediate directories didn't already exist, running the above +# command without the `-p` flag would return an error # You can redirect command input and output (stdin, stdout, and stderr). # Read from stdin until ^EOF$ and overwrite hello.py with the lines @@ -216,13 +287,22 @@ print("#stderr", file=sys.stderr) for line in sys.stdin: print(line, file=sys.stdout) EOF +# Variables will be expanded if the first "EOF" is not quoted + +# Run the hello.py Python script with various stdin, stdout, and +# stderr redirections: +python hello.py < "input.in" # pass input.in as input to the script + +python hello.py > "output.out" # redirect output from the script to output.out + +python hello.py 2> "error.err" # redirect error output to error.err -# Run hello.py with various stdin, stdout, and stderr redirections: -python hello.py < "input.in" -python hello.py > "output.out" -python hello.py 2> "error.err" python hello.py > "output-and-error.log" 2>&1 +# redirect both output and errors to output-and-error.log + python hello.py > /dev/null 2>&1 +# redirect all output and errors to the black hole, /dev/null, i.e., no output + # The output error will overwrite the file if it exists, # if you want to append instead, use ">>": python hello.py >> "output.out" 2>> "error.err" @@ -245,57 +325,75 @@ echo "#helloworld" | tee output.out >/dev/null # WARNING: `rm` commands cannot be undone rm -v output.out error.err output-and-error.log rm -r tempDir/ # recursively delete +# You can install the `trash-cli` Python package to have `trash` +# which puts files in the system trash and doesn't delete them directly +# see https://pypi.org/project/trash-cli/ if you want to be careful # Commands can be substituted within other commands using $( ): # The following command displays the number of files and directories in the # current directory. echo "There are $(ls | wc -l) items here." -# The same can be done using backticks `` but they can't be nested - the preferred way -# is to use $( ). +# The same can be done using backticks `` but they can't be nested - +# the preferred way is to use $( ). echo "There are `ls | wc -l` items here." -# Bash uses a case statement that works similarly to switch in Java and C++: +# Bash uses a `case` statement that works similarly to switch in Java and C++: case "$Variable" in - #List patterns for the conditions you want to meet + # List patterns for the conditions you want to meet 0) echo "There is a zero.";; 1) echo "There is a one.";; - *) echo "It is not null.";; + *) echo "It is not null.";; # match everything esac -# for loops iterate for as many arguments given: +# `for` loops iterate for as many arguments given: # The contents of $Variable is printed three times. for Variable in {1..3} do echo "$Variable" done +# => 1 +# => 2 +# => 3 + # Or write it the "traditional for loop" way: for ((a=1; a <= 3; a++)) do echo $a done +# => 1 +# => 2 +# => 3 # They can also be used to act on files.. -# This will run the command 'cat' on file1 and file2 +# This will run the command `cat` on file1 and file2 for Variable in file1 file2 do cat "$Variable" done # ..or the output from a command -# This will cat the output from ls. +# This will `cat` the output from `ls`. for Output in $(ls) do cat "$Output" done +# Bash can also accept patterns, like this to `cat` +# all the Markdown files in current directory +for Output in ./*.markdown +do + cat "$Output" +done + # while loop: while [ true ] do echo "loop body here..." break done +# => loop body here... # You can also define functions # Definition: @@ -306,6 +404,11 @@ function foo () echo "This is a function" return 0 } +# Call the function `foo` with two arguments, arg1 and arg2: +foo arg1 arg2 +# => Arguments work just like script arguments: arg1 arg2 +# => And: arg1 arg2... +# => This is a function # or simply bar () @@ -313,6 +416,8 @@ bar () echo "Another way to declare functions!" return 0 } +# Call the function `bar` with no arguments: +bar # => Another way to declare functions! # Calling your function foo "My name is" $Name @@ -320,42 +425,56 @@ foo "My name is" $Name # There are a lot of useful commands you should learn: # prints last 10 lines of file.txt tail -n 10 file.txt + # prints first 10 lines of file.txt head -n 10 file.txt + # sort file.txt's lines sort file.txt + # report or omit repeated lines, with -d it reports them uniq -d file.txt + # prints only the first column before the ',' character cut -d ',' -f 1 file.txt -# replaces every occurrence of 'okay' with 'great' in file.txt, (regex compatible) + +# replaces every occurrence of 'okay' with 'great' in file.txt +# (regex compatible) sed -i 's/okay/great/g' file.txt +# be aware that this -i flag means that file.txt will be changed +# -i or --in-place erase the input file (use --in-place=.backup to keep a back-up) + # print to stdout all lines of file.txt which match some regex # The example prints lines which begin with "foo" and end in "bar" grep "^foo.*bar$" file.txt + # pass the option "-c" to instead print the number of lines matching the regex grep -c "^foo.*bar$" file.txt + # Other useful options are: grep -r "^foo.*bar$" someDir/ # recursively `grep` grep -n "^foo.*bar$" file.txt # give line numbers grep -rI "^foo.*bar$" someDir/ # recursively `grep`, but ignore binary files + # perform the same initial search, but filter out the lines containing "baz" grep "^foo.*bar$" file.txt | grep -v "baz" # if you literally want to search for the string, -# and not the regex, use fgrep (or grep -F) +# and not the regex, use `fgrep` (or `grep -F`) fgrep "foobar" file.txt -# trap command allows you to execute a command when a signal is received by your script. -# Here trap command will execute rm if any one of the three listed signals is received. +# The `trap` command allows you to execute a command whenever your script +# receives a signal. Here, `trap` will execute `rm` if it receives any of the +# three listed signals. trap "rm $TEMP_FILE; exit" SIGHUP SIGINT SIGTERM # `sudo` is used to perform commands as the superuser +# usually it will ask interactively the password of superuser NAME1=$(whoami) NAME2=$(sudo whoami) echo "Was $NAME1, then became more powerful $NAME2" -# Read Bash shell builtins documentation with the bash 'help' builtin: +# Read Bash shell built-ins documentation with the bash `help` built-in: help help help help for @@ -363,12 +482,12 @@ help return help source help . -# Read Bash manpage documentation with man +# Read Bash manpage documentation with `man` apropos bash man 1 bash man bash -# Read info documentation with info (? for help) +# Read info documentation with `info` (`?` for help) apropos info | grep '^info.*(' man info info info |