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Diffstat (limited to 'bash.html.markdown')
| -rw-r--r-- | bash.html.markdown | 110 |
1 files changed, 106 insertions, 4 deletions
diff --git a/bash.html.markdown b/bash.html.markdown index 191f916a..b1a14bdb 100644 --- a/bash.html.markdown +++ b/bash.html.markdown @@ -11,6 +11,10 @@ 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"] + - ["Leo Rudberg", "https://github.com/LOZORD"] + - ["Betsy Lorton", "https://github.com/schbetsy"] + - ["John Detter", "https://github.com/jdetter"] filename: LearnBash.sh --- @@ -19,6 +23,8 @@ Nearly all examples below can be a part of a shell script or executed directly i [Read more here.](http://www.gnu.org/software/bash/manual/bashref.html) +Another recommened link: [The Command Line Crash Course](http://cli.learncodethehardway.org/book/) + ```bash #!/bin/bash # First line of the script is shebang which tells the system how to execute @@ -54,6 +60,13 @@ echo '$Variable' # 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} +# 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 occurrence of "Some" with "A" @@ -68,6 +81,12 @@ echo ${Foo:-"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} +echo {a..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's return value: $?" @@ -76,6 +95,21 @@ echo "Number of arguments passed to script: $#" echo "All arguments passed to script: $@" echo "Script's arguments separated into different variables: $1 $2..." +# Now that we know how to echo and use variables, +# let's learn some of the other basics of bash! + +# Getting our current directory is available through the command `pwd`. +# `pwd` stands for "print working directory". +# We can also use the builtin variable `$PWD`. +# Observer 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 @@ -83,24 +117,33 @@ 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 +# 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" echo "Always executed" && echo "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." fi -if [ $Name == "Daniya" ] || [ $Name == "Zach" ] +if [ "$Name" == "Daniya" ] || [ "$Name" == "Zach" ] then echo "This will run if $Name is Daniya OR Zach." fi @@ -115,12 +158,54 @@ ls # These commands have options that control their execution: ls -l # Lists every file and directory on a separate line +ls -t # Sort the directory contents by last-modified date (descending) +ls -R # Recursively `ls` this directory and all of its subdirectories # Results of the previous command can be passed to the next command as input. # grep command filters the input with provided patterns. That's how we can list # .txt files in the current directory: ls -l | grep "\.txt" +# Use `cat` to print files to stdout: +cat file.txt + +# We can also read the file using `cat`: +Contents=$(cat file.txt) +echo "START OF FILE\n$Contents\nEND OF FILE" + +# 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: $PWD") +pwd # still in first directory + +# Use `mkdir` to create new directories. +mkdir myNewDir +# The `-p` flag causes new intermediate directories to be created as necessary. +mkdir -p myNewDir/with/intermediate/directories + # You can redirect command input and output (stdin, stdout, and stderr). # Read from stdin until ^EOF$ and overwrite hello.py with the lines # between "EOF": @@ -159,7 +244,9 @@ 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 $( ): # The following command displays the number of files and directories in the @@ -250,10 +337,25 @@ sed -i 's/okay/great/g' file.txt grep "^foo.*bar$" 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$" file.txt | grep -v "baz" + # if you literally want to search for the string, # and not the regex, use fgrep (or grep -F) -fgrep "^foo.*bar$" file.txt +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. +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 |