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Diffstat (limited to 'bash.html.markdown')
| -rw-r--r-- | bash.html.markdown | 90 |
1 files changed, 60 insertions, 30 deletions
diff --git a/bash.html.markdown b/bash.html.markdown index 3f3e49eb..0385c46d 100644 --- a/bash.html.markdown +++ b/bash.html.markdown @@ -16,24 +16,27 @@ contributors: - ["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 --- -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 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. [Read more here.](http://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 +#!/usr/bin/env bash +# First line of the script is the shebang which tells the system how to execute # the script: http://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! # => 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 @@ -46,7 +49,7 @@ 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: +# 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 @@ -64,8 +67,9 @@ echo '$Variable' # => $Variable # Parameter expansion ${ }: 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 @@ -76,6 +80,11 @@ echo ${Variable/Some/A} # => A string Length=7 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 # Default value for variable echo ${Foo:-"DefaultValueIfFooIsMissingOrEmpty"} @@ -108,8 +117,8 @@ 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: $#" @@ -121,7 +130,7 @@ 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 @@ -137,7 +146,7 @@ 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" @@ -174,9 +183,19 @@ then echo "This will run if $Name is Daniya OR Zach." fi -# Redefine command 'ping' as alias to send only 5 packets +# There is also the `=~` operator, which tests a string against a Regex pattern: +Email=me@example.com +if [[ "$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 http://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 alias and use command with this name instead +# Escape the alias and use command with this name instead \ping 192.168.1.1 # Print all aliases alias -p @@ -189,14 +208,14 @@ echo $(( 10 + 5 )) # => 15 # directory with the ls command: 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 # 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: @@ -228,10 +247,13 @@ mv s0urc3.txt dst.txt # sorry, l33t hackers... # 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") @@ -256,14 +278,22 @@ 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 -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 + +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" @@ -292,11 +322,11 @@ rm -r tempDir/ # recursively delete # 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 0) echo "There is a zero.";; @@ -304,7 +334,7 @@ case "$Variable" in *) echo "It is not null.";; esac -# for loops iterate for as many arguments given: +# `for` loops iterate for as many arguments given: # The contents of $Variable is printed three times. for Variable in {1..3} do @@ -325,14 +355,14 @@ done # => 3 # They can also be used to act on files.. -# This will run the command 'cat' on file1 and file2 +# This will run the command `cat` on file1 and file2 for Variable in file1 file2 do cat "$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" @@ -412,8 +442,8 @@ grep "^foo.*bar$" file.txt | grep -v "baz" # and not the regex, use fgrep (or grep -F) fgrep "foobar" file.txt -# 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 +# 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 $TEMP_FILE; exit" SIGHUP SIGINT SIGTERM @@ -422,7 +452,7 @@ NAME1=$(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 @@ -430,12 +460,12 @@ 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 |