diff options
Diffstat (limited to 'bash.html.markdown')
| -rw-r--r-- | bash.html.markdown | 253 |
1 files changed, 203 insertions, 50 deletions
diff --git a/bash.html.markdown b/bash.html.markdown index 3b163638..0c097c27 100644 --- a/bash.html.markdown +++ b/bash.html.markdown @@ -10,6 +10,12 @@ contributors: - ["Anton Strömkvist", "http://lutic.org/"] - ["Rahil Momin", "https://github.com/iamrahil"] - ["Gregrory Kielian", "https://github.com/gskielian"] + - ["Etan Reisner", "https://github.com/deryni"] + - ["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"] filename: LearnBash.sh --- @@ -25,92 +31,193 @@ Nearly all examples below can be a part of a shell script or executed directly i # 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: 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" +Variable="Some string" # But not like this: -VARIABLE = "Some string" -# Bash will decide that VARIABLE is a command it must execute and give an error -# because it couldn't be found. +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' # => 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 variable's value, you should use $. +# 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} # => 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 +# Below are other modifications that add onto this expansion + # String substitution in variables -echo ${VARIABLE/Some/A} -# This will substitute the first occurance of "Some" with "A" +echo ${Variable/Some/A} # => A string +# This will substitute the first occurrence of "Some" with "A" # Substring from a variable -echo ${VARIABLE:0:7} +Length=7 +echo ${Variable:0:Length} # => Some st # This will return only the first 7 characters of the value # Default value for variable -echo ${FOO:-"DefaultValueIfFOOIsMissingOrEmpty"} -# This works for null (FOO=), empty string (FOO=""), zero (FOO=0) returns 0 +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. + +# Brace Expansion { } +# Used to generate arbitrary strings +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 -echo "Last program return value: $?" +echo "Last program's return value: $?" echo "Script's PID: $$" -echo "Number of arguments: $#" -echo "Scripts arguments: $@" -echo "Scripts arguments seperated in different variables: $1 $2..." +echo "Number of arguments passed to script: $#" +echo "All arguments passed to script: $@" +echo "Script's arguments separated into different variables: $1 $2..." + +# Now that we know how to echo and use variables, +# let's learn some of the other basics of bash! + +# Our current directory is available through the command `pwd`. +# `pwd` stands for "print working directory". +# We can also use the builtin variable `$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 + +# If you get too much output in your terminal, or from a script, the command +# `clear` clears your screen +clear +# Ctrl-L also works for clearing output # Reading a value from input: echo "What's your name?" -read NAME # Note that we didn't need to declare a new variable -echo Hello, $NAME! +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 -if [ $NAME -ne $USER ] +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 [ != $USER ] +# which is invalid syntax +# so the "safe" way to use potentially empty variables in bash is: +if [ "$Name" != $USER ] ... +# which, when $Name is empty, is seen by bash as: +if [ "" != $USER ] ... +# which works as expected # 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" ] && [ $AGE -eq 15 ] +if [ "$Name" == "Steve" ] && [ "$Age" -eq 15 ] then - echo "This will run if $NAME is Steve AND $AGE is 15." + echo "This will run if $Name is Steve AND $Age is 15." fi -if [ $NAME == "Daniya" ] || [ $NAME == "Zach" ] +if [ "$Name" == "Daniya" ] || [ "$Name" == "Zach" ] then - echo "This will run if $NAME is Daniya OR Zach." + echo "This will run if $Name is Daniya OR Zach." fi # Expressions are denoted with the following format: -echo $(( 10 + 5 )) +echo $(( 10 + 5 )) # => 15 -# Unlike other programming languages, bash is a shell — so it works in a context -# of current directory. You can list files and directories in the current +# Unlike other programming languages, bash is a shell so it works in the context +# of a current directory. You can list files and directories in the current # directory with the ls command: -ls +ls # Lists the files and subdirectories contained in the current directory # These commands have options that control their execution: ls -l # Lists every file and directory on a separate line +ls -t # Sorts the directory contents by last-modified date (descending) +ls -R # Recursively `ls` this directory and all of its subdirectories # Results of the previous command can be passed to the next command as input. # grep command filters the input with provided patterns. That's how we can list # .txt files in the current directory: ls -l | grep "\.txt" +# Use `cat` to print files to stdout: +cat file.txt + +# We can also read the file using `cat`: +Contents=$(cat file.txt) +echo "START OF FILE\n$Contents\nEND OF FILE" # "\n" prints a new line character +# => 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, +# so editing the copy won't affect the original (and vice versa). +# Note that it will overwrite the destination if it already exists. +cp srcFile.txt clone.txt +cp -r srcDirectory/ dst/ # recursively copy + +# Look into `scp` or `sftp` if you plan on exchanging files between computers. +# `scp` behaves very similarly to `cp`. +# `sftp` is more interactive. + +# Use `mv` to move files or directories from one place to another. +# `mv` is similar to `cp`, but it deletes the source. +# `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 +# run your command in some other directory. We have cd for changing location: +cd ~ # change 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?? + +# Use subshells to work across directories +(echo "First, I'm here: $PWD") && (cd someDir; echo "Then, I'm here: $PWD") +pwd # still in first directory + +# Use `mkdir` to create new directories. +mkdir myNewDir +# The `-p` flag causes new intermediate directories to be created as necessary. +mkdir -p myNewDir/with/intermediate/directories +# if the intermediate directories didn't already exist, running the above +# command without the `-p` flag would return an error + # You can redirect command input and output (stdin, stdout, and stderr). # Read from stdin until ^EOF$ and overwrite hello.py with the lines # between "EOF": @@ -124,17 +231,18 @@ for line in sys.stdin: print(line, file=sys.stdout) EOF -# 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 -python hello.py > /dev/null 2>&1 +# 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 # 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" -# Overwrite output.txt, append to error.err, and count lines: +# Overwrite output.out, append to error.err, and count lines: info bash 'Basic Shell Features' 'Redirections' > output.out 2>> error.err wc -l output.out error.err @@ -142,14 +250,16 @@ wc -l output.out error.err # see: man fd echo <(echo "#helloworld") -# Overwrite output.txt with "#helloworld": +# Overwrite output.out with "#helloworld": cat > output.out <(echo "#helloworld") echo "#helloworld" > output.out echo "#helloworld" | cat > output.out echo "#helloworld" | tee output.out >/dev/null # Cleanup temporary files verbosely (add '-i' for interactive) +# WARNING: `rm` commands cannot be undone rm -v output.out error.err output-and-error.log +rm -r tempDir/ # recursively delete # Commands can be substituted within other commands using $( ): # The following command displays the number of files and directories in the @@ -161,7 +271,7 @@ echo "There are $(ls | wc -l) items here." echo "There are `ls | wc -l` items here." # Bash uses a case statement that works similarly to switch in Java and C++: -case "$VARIABLE" in +case "$Variable" in #List patterns for the conditions you want to meet 0) echo "There is a zero.";; 1) echo "There is a one.";; @@ -169,30 +279,37 @@ case "$VARIABLE" in esac # for loops iterate for as many arguments given: -# The contents of $VARIABLE is printed three times. -for VARIABLE in {1..3} +# The contents of $Variable is printed three times. +for Variable in {1..3} do - echo "$VARIABLE" + echo "$Variable" done +# => 1 +# => 2 +# => 3 + # Or write it the "traditional for loop" way: for ((a=1; a <= 3; a++)) do echo $a done +# => 1 +# => 2 +# => 3 # They can also be used to act on files.. # This will run the command 'cat' on file1 and file2 -for VARIABLE in file1 file2 +for Variable in file1 file2 do - cat "$VARIABLE" + cat "$Variable" done # ..or the output from a command # This will cat the output from ls. -for OUTPUT in $(ls) +for Output in $(ls) do - cat "$OUTPUT" + cat "$Output" done # while loop: @@ -201,6 +318,7 @@ do echo "loop body here..." break done +# => loop body here... # You can also define functions # Definition: @@ -211,6 +329,11 @@ 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 () @@ -218,30 +341,60 @@ 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 +foo "My name is" $Name # There are a lot of useful commands you should learn: # prints last 10 lines of file.txt tail -n 10 file.txt + # prints first 10 lines of file.txt head -n 10 file.txt + # sort file.txt's lines sort file.txt + # report or omit repeated lines, with -d it reports them uniq -d file.txt + # prints only the first column before the ',' character cut -d ',' -f 1 file.txt -# replaces every occurrence of 'okay' with 'great' in file.txt, (regex compatible) + +# replaces every occurrence of 'okay' with 'great' in file.txt +# (regex compatible) sed -i 's/okay/great/g' file.txt -# print to stdout all lines of file.txt which match some regex, the example prints lines which begin with "foo" and end in "bar" + +# print to stdout all lines of file.txt which match some regex +# The example prints lines which begin with "foo" and end in "bar" grep "^foo.*bar$" file.txt + # pass the option "-c" to instead print the number of lines matching the regex grep -c "^foo.*bar$" file.txt -# if you literally want to search for the string, and not the regex, use fgrep (or grep -F) -fgrep "^foo.*bar$" 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) +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 +# three listed signals. +trap "rm $TEMP_FILE; exit" SIGHUP SIGINT SIGTERM + +# `sudo` is used to perform commands as the superuser +NAME1=$(whoami) +NAME2=$(sudo whoami) +echo "Was $NAME1, then became more powerful $NAME2" # Read Bash shell builtins documentation with the bash 'help' builtin: help |