[bash/en] Fix line length

This commit is contained in:
Andre Polykanine 2018-12-24 00:59:11 +02:00
parent 48c870c979
commit 4a51a5f879

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@ -20,21 +20,23 @@ contributors:
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
#!/usr/bin/env bash
# First line of the script is shebang which tells the system how to execute
# 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
@ -47,7 +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
@ -65,8 +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
@ -114,8 +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: $#"
@ -127,7 +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
@ -143,7 +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"
@ -180,7 +183,7 @@ then
echo "This will run if $Name is Daniya OR Zach."
fi
# There is also the =~ operator, which tests a string against a Regex pattern:
# There is also the `=~` operator, which tests a string against a Regex pattern:
Email=me@example.com
if [[ "$Email" =~ [a-z]+@[a-z]{2,}\.(com|net|org) ]]
then
@ -190,9 +193,9 @@ fi
# 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
# 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
@ -205,14 +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:
@ -280,10 +283,17 @@ EOF
# 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"
@ -312,11 +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.";;
@ -324,7 +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 $Variable is printed three times.
for Variable in {1..3}
do
@ -345,14 +355,14 @@ done
# => 3
# They can also be used to act on files..
# This will run the command 'cat' on file1 and file2
# This will run the command `cat` on file1 and file2
for Variable in file1 file2
do
cat "$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"
@ -432,8 +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 $TEMP_FILE; exit" SIGHUP SIGINT SIGTERM
@ -442,7 +452,7 @@ NAME1=$(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
@ -450,12 +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